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Dealing with Water-Retentive Soils

Posted by tapla z5b-6a MI (My Page) on
Sat, Sep 11, 10 at 14:02

Dealing with Water-Retentive Soils

A good friend recently asked me if putting a brick in the bottom of a container interferes with drainage? After reading the question, it occurred to me that there are aspects to the question that Ive discussed very little here at GW. It also occurred to me that I could use her question to help those who grow in heavy (water-retentive) soils. Im going to define those soils, but this isnt about disparaging soil types - its about helping you try to squeeze the most plant vitality (and the water) out of them. Heavy soils are based on fine ingredients. If the soil contains more than 30-40% of any combination of peat, coir, compost, or other fine ingredients like builders sand or topsoil, it will retain appreciable amounts of 'perched water' and remain soggy after its saturated - and this is about dealing with soggy soils.

Perched water is water that remains in the soil after the soil stops draining. If you wet a sponge & hold it by a corner until it stops draining, the water that is forced out of the sponge when you squeeze it is perched water. From the plants perspective, perched water is unhealthy because it occupies air spaces that are needed for normal root function and metabolism. The gasses produced under anoxic (airless) conditions (CO2, sulfurous compounds, methane) are also an issue. The main issue though, is that roots deprived of sufficient oxygen begin to die within hours. You dont actually see this, but the finest, most important roots die first. The plant then has to spend stored energy or current photosynthetic (food production) to regenerate lost roots - an expensive energy outlay that would otherwise have been spent on blooms, fruit, branch extension, increasing biomass, systems maintenance .. Perhaps the plant would have stored the energy for a winters rest and the spring flush of growth instead of expending it on root regeneration.

You can see that perched water, from the plants perspective, is not a good thing. From our own perspective, we think its rather convenient when we only need to water our plantings every 4-5 days, but because we cant see it, there is a sacrifice in potential growth/vitality for our convenience - like driving on low tires reduces fuel economy. How we choose to resolve this issue is of no concern to me - we all arrange our priorities & few of us are willing to water plants every hour to squeeze the last wee bit of vitality from them. Growing is about compromise in more cases than not. There is no judgment passed here on soil choice.

If you dont agree that perched water is generally a bad thing in containers, theres no need to read on. If youre still interested, Ill lay a little groundwork here before I outline some things remedial you can do to combat excess water retention. Almost all out-of-the-bag soils retain a considerable amount of perched water after they have been saturated. Each individual soil formulation will retain a specific height of perched water unique to THAT soil. No matter what the shape or size of the container - height, width, round, square the height of the PWT (perched water table) will be the same. You can fill a 1" diameter pipe with a particular soil or a 55 gallon S-shaped drum with the same soil, and both will have exactly the same PWT height.

Lets do some imagining for the purpose of illustration. Most peat or compost based soils retain in excess of 3 inches of perched water, so lets imagine a soil that retains 3 inches of perched water. Also, imagine a funnel that is 10 inches between the exit hole & the mouth and is filled with soil. Because we are imagining, the mouth is enclosed & has a drain hole in it. In your minds eye, picture the funnel filled with a soil that holds 3 inches of perched water, and the soil is saturated. If the funnel is placed so the large opening, the mouth, is down, you can see the largest possible volume of soil possible when using this container is saturated, the first 3 inches; but, turn the funnel over and what happens? We KNOW that the PWT level is constant at 3 inches, but there is a very large difference in the volume of soil in the lower 3 inches of the funnel after it is placed small end down. This means there is only a small fraction of the volume of perched water in the small-end-down application vs. the large-end-down. When you tip the funnel so the small end is down, all but a small fraction of the perched water runs out the bottom hole as the large water column seeks its 3 inch level in the small volume of soil. In a way, you have employed gravity to help you push the extra water out of the soil.

You havent affected the DRAINAGE characteristics of the soil or its level of aeration, but you HAVE affected the o/a water retention of the container. This allows air to return to the soil much faster and greatly reduces any issues associated with excess water retention. OK - we can see that tapered containers will hold a reduced VOLUME of perched water, even when drainage characteristics, aeration, and the actual height of the PWT remain unchanged, but we dont and wont all grow in funnels, so lets see how we can apply this information PRACTICALLY to other containers.

Drainage layers dont work. The soil rests on top of drainage layers, then the water perches in the soil above - just as it would if the soil was resting on the container bottom. Drainage layers simply raises the LOCATION where the PWT resides. But what if we put a brick or several bricks on the bottom of the container? Lets look at that idea, using the soil with the 3inch PWT again. Lets say the brick is 4x8x3 inches tall, and the container is a rectangle 10x12x12 inches high. The volume of soil occupied by perched water is going to be 10x12x3, or 360 cubic inches. If we add the brick to the bottom of the container so the height of the brick is 3 inches, it reduces the volume of soil that can hold perched water, so for every brick you add (4x8x3=96) you reduce the volume of soil that can hold perched water by 96 cubic inches. If you add 3 bricks, the volume of soil that holds perched water would be 360-288, or only 72 cubic inches, so you have reduced the amount of perched water in the container by 80% .. quite a feat for a brick.

Your job though, is to be sure that what you add to the bottom of the container to reduce the volume of soil that can hold perched water doesnt create stress later on when the planting has matured. Be sure the container has a large enough volume of soil to produce plants free from the stress of excessive root constriction. You dont want to trade one stress for another.

How else might we trick the water in the container into leaving? Lets think about the following in 2 dimensions, because its easier to visualize. If you look at the side view of a cylindrical or rectangular container, you see a rectangle, so imagine a cylinder or rectangle 10 inches wide or 10 inches in diameter and 8" deep. Both side views are rectangles. Now, draw a horizontal line 3 inches above the bottom to represent the level of the PWT. Remember, this line will always remain horizontal and 3 inches above the bottom. Now tip the container at a 45 degree angle and notice what happens. The profile is now a triangle with an apex pointing downward and the base is of course the line of the PWT 3 inches above the bottom. Can you see there is a much lower volume of soil in the bottom 3 inches of the triangle than in the bottom 3 inches of the rectangle? The PWT line is level at 3 inches above the apex, so by simply tilting your containers after you water, you can trick a large fraction of the unwanted perched water to exit the container. Sometimes it helps to have a drain hole on the bottom outside edge of the pot, but not always. Only when the location of the hole is above the natural level of the PWT when the pot has been tilted does it affect how much additional water might have been removed.

On the forums, Ive often talked about wicks, so Ill just touch on them lightly. If you push a wick through the drain hole and allow it to dangle several inches below the bottom of your container immediately after watering, the wick will fool the perched water into behaving as though the container was deeper than it actually is. The water will move down the wick, seeking the bottom of the container and will then be pushed off the end of the wick by the additional water moving down behind it.

A variation of the wick, is the pot-in-pot technique, in which you place/nest one container inside another container with several inches of the same soil in the bottom and fill in around the sides. Leaving the drain hole of the top container open allows an unobstructed soil bridge between containers. Water will move downward through the soil bridge from the top container into the bottom container seeking its natural level; so all of the perched water the soil is capable of holding ends up in the bottom container, leaving you with much better aeration in your growing container.

The immediately above example employs the soil in the lower container as a wick, but you can achieve the same results by partially burying containers in the yard or garden, essentially employing the earth as a giant wick. These techniques change the physical dynamics of water movement and retention from the way water normally behaves in containers to the way water behaves in the earth. Essentially, you have turned your containers into mini raised beds, from the perspective of hydrology.

What I shared doesnt mean its a good thing to use water retentive soils, simply because you have tricks to help you deal with them. For years, Ive been using highly aerated soils and biting the water more often bullet because Ive seen the considerable difference these durable and highly aerated soils make when it comes to plant growth and vitality. Many others have come to the same realization and are freely sharing their thoughts and encouragement all across the forums, so I wont go into detail about soils here.

It should also be noted that roots are the heart of the plant, and it is impossible to maximize the health and vitality of above-ground parts without first maximizing the health and vitality of roots. Healthy roots also reduce the incidence of disease and insect predation by keeping metabolisms and vitality high so the plant can maximize the production of bio-compounds essential to defense.

The soil/medium is the foundation of every conventional container planting, and plantings are not unlike buildings in that you cannot build much on a weak foundation. A good soil is much easier to grow in, and offers a much wider margin for error for growers across the board, no matter their level of experience. But regardless of what soils you choose, I hope the outline here provides you with some useful strategies if you DO find yourself having to deal with a heavy soil.

Al


Follow-Up Postings:

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RE: Dealing with Water-Retentive Soils

Good discussion Al, thanks for posting.

This is something I've been thinking about lately as I plan my containers for next year. I'll continue to experiment with using leaf mold/soil from my yard as a mix, which is definitely more water retentive than your mixes.

Some points of discussion:

* Concerning the brick example. One could conclude that using bricks in the bottom of the container will make no difference. Without the bricks the roots will be stopped at the PWT level. With the bricks, the bricks will stop the roots. So in effect you still have the same amount of aerated growing mix volume in either case.
The benefit might be that their is less stagnate water using the bricks and thus less anaerobic gas production. But I don't see how just reducing the amount of perched water volume directly helps, when the aerobic mix volume remains the same. Comments????

I did an experiment this year with 2 SWC's which I described earlier. One container was normal, but in the other I filled in the water reservoir with mix and watered it so that the bottom 2 inches of mix were always wet. This modified SWC had more aerated mix volume than the normal one, but did not have the bottom aeration/air layer that normal SWCs have.

So the normal SWC advantage was the aeration/air layer for the bottom of the roots.

Modified SWC advantage was more aerated mix volume. Disadvantage was more anaerobic gas production.

The normal SWC did much better.

* The pot in pot method, as described, seems the same as using a bigger pot. So why not just buy a bigger pot.

My plan for next year's experiment is to use a variation of the pot in pot to replicate the advantage of the SWC bottom aeration chamber. I'll use a normal pot and drill extra small holes all over the bottom. I'll put this inside another similar pot so that there is a few inches of gap between the bottoms of the pots. I'll use several wicks from the top pot to the bottom. Thus the growing pot will have the advantage of no or reduced PWT level and the advantage of an aeration layer for the bottom roots.

I've already set up a drip system so the containers can be watered several times a day automatically.

Using this pot in pot (actually tub in tub) method I'll compare growth in leaf mold mix versus the 5:1:1 mix.

Should be interesting.

Best regards and thanks again for all your sharing.


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RE: Dealing with Water-Retentive Soils

Hi Al, Thanks for taking the time to post this great thread. Very helpful, full of great information and wonderful advise and tips. Thanks for sharing it with all of us. I really appreciate you taking the time to explain it all in great detail, I'm sure it will help many.


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RE: Dealing with Water-Retentive Soils

You really know what you are talking about, thanks for the post. Norma


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sat, Sep 11, 10 at 22:15

"Concerning the brick example. One could conclude that using bricks in the bottom of the container will make no difference. Without the bricks the roots will be stopped at the PWT level. With the bricks, the bricks will stop the roots. So in effect you still have the same amount of aerated growing mix volume in either case.
The benefit might be that their is less stagnate water using the bricks and thus less anaerobic gas production. But I don't see how just reducing the amount of perched water volume directly helps, when the aerobic mix volume remains the same. Comments????"

In the container w/o the bricks or other impermeable fillers, roots don't necessarily stop at the PWT level because it comes and goes. The roots foray into the lower parts of the container as the medium dries down a little, and then part of the roots die when you water next. This is the cyclic death & regeneration of the roots I often talk about. It's better to have a given volume of well-aerated growing mix than it is to have the same volume + a layer of soil that transitions from aerated to saturated over & over.

You're also assuming that the volume of aerated soil remains the same in either case, but I was careful to point out you need to use an appropriate size container or compensate for the 'lost volume'. By using the bricks or other fillers, you're eliminating the sacrifice of roots because almost the entire volume of soil in the container can be well-aerated.

This is why SWCs don't just nest a container inside another container filled with 3" of water. They have a thin column of soil to act as a wick. The perched water table in the wick behaves just as it does in a container. If the soil is only capable of holding 3" of perched water, ALL the perched water will remain in the wick. The rest of the water that is drawn upward cannot fill macro-pores. It moves upward from particle to particle, and can only move upward through the capillary action of micro-pores.

If what you posed was true "I don't see how just reducing the amount of perched water volume directly helps, when the aerobic mix volume remains the same", there would be no reason to worry about perched water in any application. Yes?

The pot in pot method, as described, seems the same as using a bigger pot. So why not just buy a bigger pot.

.... because in a bigger pot, you have the PWT to deal with. Commercial growers often employ pot-in-pot or pot-in-trench methods to eliminate the effects of the a PWT. The reason the 5:1:1 mix works so well compared to heavier soils is because, when properly made, it holds only very small volumes of perched water. You get the benefit of the bricks w/o the bricks, plus superior aeration.

"I'll put this inside another similar pot so that there is a few inches of gap between the bottoms of the pots. I'll use several wicks from the top pot to the bottom. Thus the growing pot will have the advantage of no or reduced PWT level and the advantage of an aeration layer for the bottom roots."

The Ups-a-Daisy company sent me the materials to test this year that follow closely what you are saying. I haven't finished yet, so haven't reported the results to Jeff, but I can say that it's unlikely you'll see a difference between what you propose and just the container with a wick (w/o the divider), but please don't scrub your experiment based on what I'm saying. Have fun! ;o)

FWIW - it's still better to use a homogeneous soil that is free-draining and durable from container bottom to top; the reason being if the soil is water-retentive to the point you need to act on it, the level of aeration cannot be as good as a soil that doesn't require remedial attention.

Take care.

Thanks for the kind words, Nance & Norma.

Al


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the frequency of watering tradeoff

I've been thinking about the tradeoff tapla mentions often. It's not practical for many to water several times per day. However, there are solar powered water pumps out there, for decorative fountains and such. I've been thinking maybe there's a way to collect the runoff from several containers and having it automatically pumped back into them.

I imagine a constant flow of water would be as bad as too much water retention. Maybe with some timed valves each of many containers could get watered once per hour for example.

How much time would be needed between waterings if the ideal soil mix were used?


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RE: Dealing with Water-Retentive Soils

Thank You Al~
Nancy and Norma put it well. :)(hello ladies :)
This is a big help to me, and I'm sure many will learn from this.
Your time and caring is greatly apriciated.
JJ


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RE: Dealing with heavy Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sat, Sep 11, 10 at 22:36

You'll need to give some careful consideration to a system that recycles the effluent because of several issues; among them are pH fluctuations, and nutrient imbalances. You'll still need to change the fertigation solution very frequently unless you have the ability to analyze what is in the solution. E.g., if you chose a soluble fertilizer like 20-20-20, you would quickly be left with a solution that was deficient in N, or very high in P and K. Essentially, you're talking about hydroponics here.

"How much time would be needed between waterings if the ideal soil mix were used?"

It depends on the individual. I water about 300 containers daily in the summer, and about 100 daily or every other day during the winter. I like my soils very fast, so for me, the ideal soil is one that requires daily watering.

Others might be horrified at the thought of watering taking 1-2 hours daily. It also depends on whether you're looking toward 'ideal' from your perspective or the plant's. The plant thinks ideal comes attached to the phrase 'the more the merrier'. The plant likes fast soils with lots of air and that 'damp, not wet' level of moisture, but another grower might like to water only once a week in a half hour slot between favorite TV shows.

I'm not being flip when I say ideal is what you perceive as the right balance between what your plant wants and what you're willing to provide, but what's important is understanding how to get there.

Thanks, JJ. I wondered when you'd be around. It was actually your brick question that gave me the idea for the thread. ;o)

Al


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RE: Dealing with Water-Retentive Soils

Hi Al~
I saw this earlier, but my computer decided I would post later. ;) lol..

I kinda thought it was my brick question when I saw this over in Figs. ;)

It's a great thread with alot of thought put into it, and I know will help many.

In a bit, when it's quiet, I will go through it again and then save it.

Thanks again,
JJ


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RE: Dealing with Water-Retentive Soils

It took me a re-read on the brick example to understand the concept. My first read thought you'd say "a brick is worthless, since the perched water will just reside on top of the brick, because it is just acting as a solid drainage layer, really just reducing the amount of total soil volume". But after re-reading it, I understand now. I've never examined how SWC's work but your second explanation of the soil-wick (small column of soil) now makes sense how they've designed the watering & drainage method.

The brick method does work to reduce perched water. This is mostly because the brick is SMALLER than the base of the container. It is replacing a large percentage of the soil residing on the "floor space", i.e. bottom of the container, thereby leaving small amounts of soil around it to hold the perched water and be the "conduit" to drain it out the bottom holes. To further understand he concept, imagine you placed a brick that occupied 100% of the bottom of the container. This would be worthless, since it is a non-permeable drainage layer. The PWT would be identical but would now reside ABOVE the brick and 3" tall, since you only created a new container bottom. This theoretical example is flawed because you'd obviously be blocking your drain holes ;-)

But I think it's helpful for beginners to note that within the example, it is realistically only helpful to add at MOST 3 bricks. The bricks weren't stacked in the example, they were laid next to each other to reduce the soil exposed on the "floor" of the container. If you tried to add a fourth brick, it would have to be stacked on top of the other 3 and would not do much other than reducing soil volume, as there was little PWT left to reduce.

I personally would rather just use a good wick, thereby leaving more soil available for root occupation later (as you hinted to).

I realize for the sharp folks out there, this is like a message from Mr. States-the-Obvious.


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sun, Sep 12, 10 at 9:43

It's difficult to cover all the bases. It seemed to me that it was a natural step to go from the funnel illustration to the brick, but you're the second person who said the brick illustration wasn't clear enough, so I appreciate the added clarity of your offering.

For additional clarity - you MUST have at least 1 column of soil that reaches from the bottom of the pot to the main body of soil. As noted immediately above, if you were able to cover the bottom completely with bricks (or other), the water WOULD perch above the bricks because you would simply be creating another container bottom, but if there are cracks/crevices between the bricks, the perched water can only occupy 3 inches of soil (this is 3" for the purpose of this illustration. PWT heights vary soil composition). Your job is to reduce the amount of soil in the lower 3 inches of the container, but not eliminate ALL the soil in that 3 inches, as you would be doing with a drainage layer or a false bottom wedged into the container.

I also appreciate the clarification that it would do no good to stack the bricks. It would also be less efficient if you stood a brick on end, or on edge so the height was any more than 3 inches. We're only interested in displacing soil below the level of the PWT height, which in this example happens to be 3 inches. If you stood the brick in the example on end, you would only be displacing a volume of soil = to the two horizontal dimensions of the brick + the height of the PWT. That would be 4x3x3 or 36 cubic inches as opposed to the brick lying with the 3 inch dimension as the height, which is 4x8x3 inches or 96 cubic inches.

The very simply practical application is this: Get a little larger container than you would normally use, unless the container is more than large enough already. Add bricks or other solid objects that won't absorb water to the bottom of the container to at least the height of the PWT your soil supports, but leave a little space so some of the soil forms a bridge between the main body of soil and the bottom of the container. By doing this, you can virtually eliminate the soggy layer of soil you often find yourself having to work around when using heavier soils.

In some cases, a wick may not be as effective as the illustration I just gave. The soil CAN hold water so tightly that the wick isn't 100% effective. BUT, the wick does have one advantage. After the planting has matured, you may find you can't water as often as your plants need to be watered. If you're using the wick, you simply remove it, and the PWT returns. Only NOW, the planting has matured and the water in the PWT is being used much faster, so its affect on the cyclic death & regeneration of roots is greatly reduced from when the plant was essentially over-potted simply because it hadn't grown into its container yet. This option isn't open to you with bricks as it is with a wick.

Thanks again for the added clarity.

Al


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RE: Dealing with Water-Retentive Soils

Hi Jojo..I forgot it was me that got you started on these mixes and introduced you to this forum..I am happy for that for many reasons!!>-)

Al, you are a blessing from above for all our precious plants and to us personaly...

Always appreciated man. and yes, I understand everything you said on this...lol

You are my good friend!

Mike


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sun, Sep 12, 10 at 14:20

It won't increase or improve drainage or aeration, but it WILL reduce the volume of perched water that takes up residence at the bottom of the container, which is a plus. Keep in mind the tips are to help you deal with the effects of excess water retention, but they won't help you with aeration beyond the fact that air will return to the soil in the bottom of the pot faster because of the reduced volume of water in the PWT - but that is with the proviso that you aren't over-watering. Over-watering quickly negates any gains made because the maximum ht of the PWT remains the same until the planting is able to use the water that remains in the PWT. One of the main benefits of utilizing the 'trickery' is that (hopefully) it will allow you to water copiously when water is required, where you might not have been able to do so w/o ill effects if you had not taken steps to reduce the volume of perched water in the PWT.

Al


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Water-Retentive Soil Tricks

  • Posted by tapla z5b-6a MI (My Page) on
    Sun, Sep 12, 10 at 14:22

Thanks, Mike - JJ, too if I didn't already thank you. ;o)

Al


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RE: Dealing with Water-Retentive Soils

Sweet_chicken,

Take my word for it..Take all this in and you will be able to come back here and say you have finally kept a plant alive longer than a month..:-)

Mike


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RE: Dealing with Water-Retentive Soils

Hi Al, a follow up question:

A "normal" pot has a few larger drainage holes and it usually sits in a plastic tray to catch the runoff.

Would creating a better aeration bottom be of much benefit? Basically drilling lots of little holes in the bottom of the pot and then setting the pot up using bricks (or something) so that it is easy for air to get underneath the pot.

And as mentioned you can add a wick.

Thanks


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sun, Sep 12, 10 at 16:50

The more highly aerated the soil is, the greater would be the benefit, but it would still be minor. If using heavy soils, the primary benefit would lie in that it might allow additional evaporation, which would combine with transpiration to speed the elimination of perched water. If it was a highly aerated soil, it would improve gas exchange a little, and it's contribution in the way of evaporation wouldn't matter much because the soil is already well-aerated. I should probably note that if you have arranged for the pot to sit above a collection saucer, the water in the saucer would have some affect on the air surrounding the holes in the bottom - like raising RH, so you COULD shoot yourself in the foot (because there would be little evaporation at high humidity. Most of the gas exchange in containers occurs when you water, which pushes old gasses out & draws fresh air in behind the downward-moving water - which is another reason fast soils work so well - they need more frequent watering, so more frequent and better gas exchange is assured.

Al


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RE: Dealing with Water-Retentive Soils

I fill the bottoms of my large pots with anything I have - old plastic flower pots, empty water bottles, Styrofoam, etc. to create air space on the bottom 1/3 of the pot. I always have extra holes drilled along the bottom/side of my pots.

I do this with the pots containing my summer plantings which are mostly annuals. I have shallow saucers under some.

I use Miracle Gro mixed with some bark as my planting media. Water has nowhere to go except out. No perched water and plenty of air.

I grew tomatoes this year which produced very well grown the same way.

Jane


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RE: Dealing with Water-Retentive Soils

Thanks Al!

Wish I'd known this before killing my containerized heirloom mirliton/chayote with poorly draining planting mix. Prof. Hill down in LA has been sending out info on keeping containerized mirliton in the proper medium for growing. I have sent him an email with your above post. He will probably share it with the folks on his mailing list. Hope this is OK with you.

DL


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RE: Dealing with Water-Retentive Soils

For years I have been reading Al's posts using the "perched water" term. I do understand, it and have no problem with the concept, only the name bothered me. In his explanation of the use of a sponge for demonstration purposes, I recognized exactly the same demo used to explain "field capacity". For those of us making our plantings in the garden (NOT in a container)our soil is being constantly fluctuating between field capacity water and the wilting point. Of course in the garden we have gravity working with bottomless soil to prevent the soil ever remaining at "field capacity" whether we have anything growing in the soil or not. The other Al


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RE: Dealing with Water-Retentive Soils

Thanks, Al!

The principles that you've shared have helped me to maximize the vitality
of many, many plant species. Even before I was able to locate Turface, I had a
solid grasp of particle-size and particle durability that allowed me to build soils
of suitable substitution - Pumice and quartz gravel being the primary concessions.

Friends of mine, who never had much interest in gardening, have converted their containers
to gritty mixes - both the 5-1-1 and THE Gritty Mix proper. Although I've continued
to provide them help with fertigation and application of Lime or Epsom salts, I predict that
they'll be fully autonomous by next Spring. If I can get them to use Foliage Pro, we can
free up even more space in the fertilizer cabinet.

It seems fashionable to balk at the idea of straining, sifting, or rinsing ingredients,
but with a small investment of labor up front - locating the materials, prepping materials,
and combining - one can literally save hours (and plants) in the long run.

Josh


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Mon, Sep 13, 10 at 17:07

DL - Sure - I don't mind at all. I posted in the hope that those who don't fully understand how water behaves in soils might at least get some benefit from the tips.

Al - I often use the term 'container capacity', which describes the soil in the container after it's been fully saturated and has just stopped draining - same as field capacity - only applied to containers. The term 'perched' water is an actual geologic term that describes water that resides tightly held in fine soils, 'perched' above porous and fast draining substrates. Just as water perches in water-retentive soils above drainage layers and container bottoms, it also perches in clay and silt above sand, gravel, scree ..... Now you know where I borrowed the term from. ;o)

An aside: If a soil supports perched water, you WILL have perched water in your container unless you take steps to eliminate it. Drainage layers do NOT eliminate perched water, and fillers only eliminate a portion of the perched water. The number of holes on the bottom or sides of a container have nothing to do with improving drainage or aeration. They may have SOME impact on gas exchange if the soil is well-aerated, but the effect will be minimal with heavy soils. Extra holes do allow for increased evaporative water loss, so in that capacity they reduce the level of perched water in a container faster than if they were there, but the number of holes on the bottom/sides of the container have nothing to do with a reduction of the height of the PWT or the volume of water in the PWT.

Thank you, Josh - You've always had an open mind and were able to quickly grasp the concepts. Sure, it takes some time and effort to build a premium soil, but once you locate sources & get your methodology down, it's really not much of an investment in time OR effort. The 5:1:1 mix costs about 1/3-1/2 the price of commercially prepared bagged soils. The gritty mix costs more, and is more expensive, but I want my plants to have the best chance I'm able to offer them to grow to their potential. In the long run, I feel you'll spend less time trying to fix things and have more time to make 30 qt batches of spaghetti sauce from scratch (like I did yesterday - recipe for a small batch on request) ;o) than if you're fighting a plethora of ills, the roots of which you can trace back to poor soils/habits. You might be able to save $ by employing a poor soil, but I wouldn't expect to save time or effort.

For those who feel their soils or methods are good enough - I have to agree. I can't determine for them what is good enough, and they shouldn't decide for others, either. I have no interest in trying to convince someone to change when they don't want to. I'm only interested in interacting with those who, like me, want to improve their skills and/or widen their horizons. There are LOTS of them around, and I find them fun and refreshing, their enthusiasm contagious.

Al


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RE: Dealing with Water-Retentive Soils

Why isn't the perched water table wicked upwards, as the upper layers of soil dry out?

Is it possible that it is, and this mitigates the problems of water retentive soils?


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Tue, Sep 14, 10 at 10:50

The 'why' part is explained in the original post, but the short version is: at some point, the weight of the water column pushing down (gravity) and the capillary pull (upward) of the soil reach a stasis, which determines the maximum height of the PWT. Some water does move upward out of the PWT by diffusion from particle to particle, but what delineates the PWT from the soil above is the fact that macro-pores in the PWT are also full of water where only micro-pores above the PWT level are capable of holding water.

Al


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RE: Dealing with Water-Retentive Soils

However the PWT will eventually disappear - whether by capillary action or evaporation - providing you wait long enough before watering again.

I'm not disagreeing, by the way, I've inspected plenty of containers and seen damage caused by PWTs. I'm just curious as to how some people manage to grow successfully in heavy potting mixes.

I've a friend who grows decent herbs in *garden soil* in styrofoam boxes! He very rarely waters them and I suspect this is the trick: perched water must have enough time to diffuse while the medium remains moist enough to keep the plants hydrated. When you think about it this is essentially the same principal in action as in a sub-irrigated container. It's terribly unscientific and I'm not advocating this approach, I just want to know how he gets away with it!


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Wed, Sep 15, 10 at 4:57

With a small fire in a waste basket, the prudent thing to do would be either to prevent it in the first place, or failing that, to deal with it quickly. There's a much higher likelihood the fire will cause larger problems down the road if you take the position 'if you wait long enough it will eventually go out', even though the statement is entirely true.

Many people are entirely happy with the results of their growing efforts and have no desire to expend energy on exploring options. The largest % of issues on this forum related to soils involves water retention. There are some very rigid scientific principles that can tell us whether or not you are dealing with a PWT. You can't in one breath say that you grow in MG potting soil and in the next say you don't have perched water - the same holds with the topsoil/compost/chopped celery, and pine nuts approach. ALL the fine soils hold perched water, and perched water begins to kill roots very quickly. If you don't eliminate it, you simply accept some cyclic death/regeneration of roots in the container. I'm not offering this information as a judgement call, but it's there as a by-product of heavy soils. You can't wish it away or simply say the issue isn't there.

If you don't think you or your friend have issues - there is no need to worry about changing anything. There are hundreds, and over the years, thousands of people who have recognized problems with heavy soils and have used the information to take a big step forward in their abilities. No need to take my word for it, the forums are full of people who have offered some version of "Holy Cow! Now I understand why I have been having such problems with .....", then they describe their soil.

You CAN get away with heavy soils by watering in sips, but then you have the issue of salt build-up and still have the issue of water retention should you over-water or should it happen to rain. The added aeration of soils made from larger particles is also an important part of why the highly aerated soils work so much better. What we grow in is a personal choice. I don't chase anyone, twisting arms and trying to convince anyone to abandon what they are comfortable with. I rely on scientific principles, reliable information, plenty of my own practical experience, and very importantly - the practical experience of thousands of others to let people know there IS a better way, if they want to try it. If they don't, I lose nothing & hopefully, the source of some of their problems become clear; and, with treads like this one, they are able to learn a few tips on how to deal with heavy soils to mitigate negatives.

Al


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Wed, Sep 15, 10 at 6:55

I'm sorry - the 'why' part alluded to upthread isn't explained in THIS original post. It's explained in the original post at the link I left below.

Al

Here is a link that might be useful: About soils & water retention


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RE: Dealing with Water-Retentive Soils

You didn't mention your zone or light conditions. I grow many outdoor plants in bagged potting mix without any problems. My light is full sun, all day. My pots dry out quickly, I always check the soil before watering.

Not a problem depending on your light and control of your watering.

Jane


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sat, Sep 18, 10 at 10:41

I just left a good part of this response on another thread, but I think it's appropriate here, too:

Light is a very important, no, KEY element in determining how well your plants grow, and how they grow insofar as growth habit is concerned, but light isn't enough to trump the effects of a poor or water-retentive soil. Plants have rhythms set to day length and their own internal clocks (search endogenous and circadian rhythms) so they slow down or change growth patterns during a part of their growth cycle regardless of light levels. Even plants that grow exactly on the equator respond to subtle photo-periodic changes and intrinsic rhythms. Slowed growth, regardless of the source, increases the potential of unwanted issues from heavy soils.

Even if we are able to provide perfect lighting for every plant we grow, it still wouldn't eliminate the limiting affects of poor soils, though it CAN help mitigate them.

Watering technique is also extremely important in container culture. The heavier and more water-retentive the soil is, the more critical proper technique is and the narrower the margin for grower error. If we water copiously to flush accumulating salts from the soil, often we face the specter of root rot or a % of the finest roots dying while we wait for air to return to the soil. If we try to control water applications by watering in sips to prevent root issues, we know that salts from fertilizer solutions and tap water accumulate in the soil. There is also the issue of rain that can confound our attempts to control water applications by watering in sips.

Actually, all these issues are what prompted me to start this thread in the first place. ;o)

Al


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RE: Dealing with Water-Retentive Soils

Light can 'trump' water-retentive mixes and over-watering. When plant growth is steady and rapid, the plant is utilizing water. A under-lit plant is barely growing.

Neither is an ideal growing condition, but light will always promote growth thus increasing the plants need for water. Underlit plants will stagnate and decline no matter what mix the plant grows in.


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sat, Sep 18, 10 at 14:43

I do understand that improving light can improve growth; but this is true only if light is the limiting factor. You'll find that improving or even making perfect one potential limiting factor (light) cannot negate (trump) the affects of another limiting factor. A quick review of Liebig's Law of the Minimum will clearly confirm this fact.

Please read about Liebig's Law by clicking on this link. Particularly germane to the discussion is this portion of the text:

"... For example, the growth of an organism such as a plant may be dependent on a number of different factors, such as sunlight or mineral nutrients (e.g. nitrate or phosphate). The availability of these may vary, such that at any given time one is more limiting than the others. Liebig's Law states that growth only occurs at the rate permitted by the most limiting [factor]."

This universally accepted concept very clearly illustrates that making light levels perfect does NOT trump the negative influence of heavy soils or over-watering. Exposing plants to perfect light levels, perfect nutrition, perfect soils, perfect any cultural influence, simply eliminates those cultural influences as potential limiting factors.

If you feel you can counter this point with something scientific, please feel free - I'm anxious to listen and learn, but I don't wish to continue to argue the same point another time.

Thank you.

Al


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RE: Dealing with Water-Retentive Soils

O.K.
What's up? GW glitch or what? I know I saw more posts here earlier, and was planning on catching up on some reading. Where did they go?

JoJo


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RE: Dealing with Water-Retentive Soils

Will someone please tell me what is going on ? i have been enjoying what Al and others have to say until for some reason the things people were saying were just thrown away.Why should I come here when good information is erased?what is going on around here, i know there are a lot of writings missing?


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sun, Sep 19, 10 at 17:45

Sorry, guys. I had written a note to GW admin asking them to review this thread because of the nature of some posts that have since been deleted, which is why it appears that some of the info I had posted had been deleted along with it. I don't think they deleted my posts because they found anything offensive in them, I was careful to ensure there wasn't; it's just that they were replies to posts no longer here, so not much has actually been lost ...... same thing on the 'Pine Needles Thread'.

I'm working on another thread that goes into more detail about limiting factors and how they affect plant growth. Actually, having to explain why perfecting one or all of the factors that potentially limit growth can't make up for the one factor that does limit growth was a good thing. It gave me an idea for another thread that I'm hoping will garner some interest and start another fruitful discussion. I hope you'll watch for it.

Thanks for being so attentive! ;o)

Al


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RE: Dealing with Water-Retentive Soils

Al, thanks for supplying us readers with some great information. Gosh, i've learned so much from you about growing in containers, and just wanted to let you know that it is greatly appreciated. My plants appreciate it, too!

EG


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Mon, Sep 20, 10 at 14:57

You're welcome. I often speak at various gatherings - mostly gardening or garden-related clubs, MG groups and such. Often, at the end of the talk when thank yous are being expressed, I ask the group to take the time to teach others what they've learned and what they know. So many times, the thought that I would have arrived at wherever it is I am in my journey to being able to grow plants well so much sooner, had someone been available to share some of the things I'm able to share with you guys.

I realize that some people can't be helped, or don't want my help. You can't push someone up a ladder unless they want to climb, but the rewards that come in the form of personal satisfaction from helping people like you, and so many others, seem like a natural extension of the rewards I get from nurturing plants. Nurturing plants/nurturing plant people - it doesn't matter much - the rewards are really very similar ....... and either way, it's enjoyable. People make better friends, though. ;o)

Thank you, EG.

Al


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RE: Dealing with Water-Retentive Soils

Al - I have several Earthboxes. What type of planting medium would you use and would you still use the 2 cups of granular fertilizer and plastic "shower cap" covering that is recommended? I had been using a peat potting mix with 8-10-10 or 16-4-8, depending what I was growing.

What do you suggest for the planting medium and fertilizer? Thanks so much for you help.

Christine


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a MI (My Page) on
    Sat, Oct 9, 10 at 10:29

Hi, Christine. I don't use SWCs, so would defer to others with more practical experience, but from the discussions I've had, it seems like modifying the 5:1:1 mix to something like 5:3:1, bark:peat:perlite has worked well in the past, but the best ratio will depend on the size of the particles of the largest fraction of the soil, that being the bark.

I would find a thread specifically directed at the discussion of SWCs and ask about the +/-s of using fertilizer strips vs CRFs vs fertigating (watering + fertilizing) with solubles from the top or bottom.

I'm guessing the 'shower cap' is suggested to help keep water vapor from evaporating as it nears the surface of the soil, thus keeping the soil more evenly moist and providing a favorable environment for the important fine roots in a larger % of the soil, and to facilitate dissolution of the fertilizer in the strip. I'm envisioning it as also serving to slow the upward creep in pH usually associated with the accumulation of (bi)carbonates in the media. The more water that evaporates from the surface, the more carbonates are left behind. These accumulating compounds drive alkalinity/pH upward; and since we're not watering from above, there is no way to flush them from the soil.

Best luck!

Al


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RE: Dealing with Water-Retentive Soils

  • Posted by jodik 5 Central IL (My Page) on
    Tue, Oct 12, 10 at 16:21

I'm eager to learn the scientific reasoning behind the idea that light can trump fine, soggy soils and excessive watering. This is something I've never heard of, nor would I think it prudent to keep a declining plant in a detrimental medium, or continue to over-water, when it's too easy to just re-pot using a better medium and stop over-watering.

The right amount of light is essential to good plant growth... this is an elementary piece of gardening knowledge, and it goes without saying, but how adding more light will cure a soil issue and over-watering is something I don't understand. Please expound, will you, Jane? I'm very eager to learn exactly how light will trump my poor soils and heavy watering hand.

And a note to tapla... thank you so much for your continued diligence in sharing prudent and factual information. I'm not certain if I've mentioned it, but my lavender flowered Dendrobium grown in mid-light, in my rendition of your medium mix, has very healthy roots and is about to bloom for the first time since I rescued it from a clearance cart at Lowe's! Thank you, for all you do! :-)


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RE: Dealing with Water-Retentive Soils

Interesting article. I had the same "what's the point of the brick" question as emgardener, but you answered that well.

Now I have one that I don't see answered, though the double-pot techniques kind of approaches it.

...

Why not use a very deep pot? Put the PWT down below where the roots would naturally want to go?


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RE: Dealing with Water-Retentive Soils

To preface, I'm not at all agreeing with jane_ny's comment, but I think the gist of what she's saying is important. Sorry if this has been rehashed before.

One of the well accepted limitations of Liebig's Law of the Minimum is that each factor must be as close to independent as possible. When factors interact, the model becomes less predictive. When looking at the big picture though, Liebig's Law is of course still extremely useful.

In the case of increased light, and what I think is the implied increase in temperature, these factors interact with the "excess water" factor.

For example, suppose I have two plants in a water retentive medium. I put one in an area where it gets some afternoon shade (Plant A) I put the other in the middle of the lawn where it will get the full heat of the sun all day (Plant B) Identical plants in a coarse, well drained medium are also put in these situations (Plant C and D). All plants are watered exactly the same amount, once a day.

Plant A and B are both limited by water-retentive soil. Plant B will be forced to transpire to maintain leaf temperature. It can keep its stomata open because it has a large supply of water available in its pot, which maintains leaf water potential. This reduces forced photorespiration caused by the closing of stomata to prevent water loss (triggered by leaf water potential). Light in excess of photosynthetic capacity can still be used up by photorespiration to prevent even more harmful light-triggered reactions. As the water is used up on a daily basis very quickly, the problems of an anoxic perched water table are lessened.

Plant A feels the full effects of a perched water table, and has decreased growth as a result.

Plant C has the ideal conditions for this particular plant - bright light in the morning for optimum photosynthesis, with a soil medium that is both evenly moist and has plenty of porosity for air. It flourishes.

Plant D has the same great soil, but oppressive sunlight and heat in the afternoon. It cannot maintain open stomata and cool itself because its soil medium doesn't retain enough water. It suffers from decreased growth due to the water stress and excessive light and leaf temperatures.

So in this case, excess light that might be a limiting factor alone interacts with excess water-retention to decrease (not eliminate) each of their negative effects.

Does more light "trump" overwatering? I'm not really sure what that means. Light in excess of what would normally be "ideal" may reduce the effects of overwatering. If for some reason you insist on using a water retentive soil, putting your plant in a place where the soil be relatively dry by the end of the day is one way to decrease the overall stress on the plant. It's much better of course, to use a good medium and the appropriate amount of light.

I'm not presuming that this argument is news to Al or anyone else here, but I really needed to write it out for myself. Liebig's law is one of the most useful tools of biology, but it's not a dogma.. it has to be fine tuned when you approach the details and nuances of such a complicated system.

Feel free to now tear this apart, you won't hurt my feelings. Just explain why.

PS: I know I'm conflating light and heat in some places, but unless we're talking about grow lights, they do usually come together.


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RE: Dealing with Water-Retentive Soils

These topics are the best!!

A soil that holds water- When watered for a day or so the plant is in too much water, for a few days it is in too little water to "dry" properly.

With the 511 it could hold water and air in the right ratios!


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RE: Dealing with Water-Retentive Soils

Oh wow. I didn't realize this thread was so old!


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RE: Dealing with Water-Retentive Soils

  • Posted by dsws none (My Page) on
    Mon, Jan 7, 13 at 14:48

After reading the OP, I don't see why a coarser / more-porous layer would be so different from a wick.

It seems to me as though the best configuration would be a continuous gradation from very coarse material at the bottom (that has air space even when it's just been soaked), to slightly finer material on top of it (that has air space when just soaked, but only because the stuff underneath it provides a little help to wick the water downward), and so on to peat-based medium everywhere above three inches (or whatever the saturation height is for the medium at hand).

That's for the configuration it settles to: you would want some extra height of coarse material to allow for some finer stuff from each layer falling or being washed into the gaps in the next layer down. But any further coarseness of the upper layers just reduces your water-holding capacity without providing any additional aeration.


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Mon, Jan 7, 13 at 15:15

If you wish to construct that type of layering system, it can be made to be effective.

Al


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RE: Dealing with Water-Retentive Soils

Thank you.

Btw, I may sound from time to time as though I'm disagreeing just to be contrary. What I'm actually trying to do is bash my half-baked notions and half-remembered understandings against others' practical knowledge, to see what breaks. I expect it to be my arguments that fall apart most of the time, and I appreciate the many well-informed explanations I've seen in your posts on this forum.

Edit: And I edit compulsively. I don't have any excuse for that. It's just habit.

This post was edited by dsws on Mon, Jan 7, 13 at 16:32


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RE: Dealing with Water-Retentive Soils

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Mon, Jan 7, 13 at 17:14

Thanks for mentioning that. I had noted how many of my old threads you were bumping, and was hoping the reason was one that would end up turning into a learning opportunity for all of us. It looks like you have most of the pieces assembled, and will be able to make quick work of what might be missing, so good for you!

Al


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RE: Dealing with Water-Retentive Soils

Another great in depth article, Al... thank you!


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RE: Dealing with Water-Retentive Soils

  • Posted by dsws none (My Page) on
    Tue, Jan 8, 13 at 16:50

Part of what I've been thinking as I read about water in soil is going back and forth between thinking of the water as sitting on the bottom or hanging from the top. It does both.

An image that may help make this idea clear is a slinky.

When you water thoroughly, you put in the slinky, stacked all the way from bottom to top. Then the slinky slithers out the bottom until it's hanging from the top all the way to the hole in the bottom. As the slinky goes out the hole, it vanishes. When there are only a few turns of slinky sitting on the bottom, their weight is no longer enough to overcome friction and push the slinky out the hole. Those few turns are sitting on the bottom; the rest of the slinky is hanging from the top.

Changing the medium is like putting a fluid around the slinky for buoyancy. If the fluid is so dense that the slinky actually floats, that corresponds to a solid lump of clay. There's no air space, no matter how tall the container is. Gritty mix is like air, so that only one or two turns of slinky sit on the bottom.

One way this analogy is a little off is that slinkies can't flow sideways, but water can. To imagine what happens with a brick or a wick or a funnel, you have to imagine turns of slinky being able to jump sideways when the tension on the next slinky pulls harder than the tension on the slinky they're in.


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