Container Soil Basics: a compilation

lathyrus_odoratus(5A-IL)July 14, 2009

I just reviewed all 8 threads in the Container Soil/Retention series started by Tapla aka Al. I realized that many questions kept getting asked over and over. It's hard to wade through all those posts! I thought we might try to make it a bit easier for Al, justaguy, or anyone else answering questions about these mixes. Please, Al and justaguy, correct any mistakes I've made.

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Bark fines is a toughie. Packages don't list it that way, so many people are/were confused. Basically, this is saying "fine bark". Using the words fines is a descriptor of it.

The goal here is to use pine, fir, or hemlock (those are most common) pieces of bark where most pieces are 1/8" in size. Some can be larger, some smaller. You do not have to screen these.

You can buy either fresh or composted. Composted is preferred because of an issue with nitrogen (N) when they are fresh. If you use fresh, just use a bit more N fertilizer.

To find it, read the ingredients on the label and look for pine, fir or hemlock bark. You usually want no additives, but sometimes the additives are also something you want to use in your mix. Use your best judgment.

The product might be called any of the following: mulch, pine mulch, pine bark mulch, bark fines, clay buster, or mini nuggests. Brand names include things like Vita Bark (fir) for Orchids, Soil-Pep.

Ask to see it. Look at Al's picture. It should have some fine pieces and maybe some large ones, but the majority around 1/8" in size.

    Bookmark   July 14, 2009 at 8:45PM
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Turface is another ingredient that seems hard to find for some people. Turface is basically calcined clay that has been fired (heated) at a very high temperature, making it very, very hard. Turface has several advantages: it holds water well, degrades slowly, offers good drainage and aeration, provided space between the particles, holds nutrients well, is an excellent CEC, and is good when you need stability in your soil.

Turface is the brand name for one type of this product. You want the product called MVP - this is the right size. At one time, there was also a Turface Allsport that was the same size. Not sure if it's still called that.

Other products that are also made of fired clay that you could use include PlayBall and ProChoice Infield Conditioner. Some oil dry products are also fired at high temps, but some are not. Always test any oil dry before you buy a large quantity. Put some in water and let it sit for a day or so. If it dissolves, it's not going to work. NAPA sells at least one product, a floor dry, that works. There is an acquatic soil you can get that is the same thing, though more expensive. Schultz used to sell a clay soil conditioner, but do not make it anymore.

There are other products you can get that will take the place of Turface. DE, or diatomaceous earth, lava rock, utelite fines, haydite, and Espoma Soil Perfector are all possibilities.

Per sizing, you want this to be uniform in size. Again, see Al's picture. I included a link to it. The coin in his image is a dime.

You cannot use pea gravel in most cases because of sizing issues.

Picture Key, clockwise from noon: bark fines,

Here is a link that might be useful:

    Bookmark   July 14, 2009 at 9:06PM
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Oops, changed pictures at the last minute - don't pay attention to the last line in the previous post. The Turface is the stuff in the lower left of the image. The white gravel is crushed granite.

    Bookmark   July 14, 2009 at 9:07PM
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Perlite is commonly found in garden centers. Al needs to add his two cents here, but I think he uses a medium size. I am also not sure how you can tell what size it is.

If you do not have perlite, Turface or pumice can be substituted.

    Bookmark   July 14, 2009 at 9:09PM
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Granite, or a similar item, can be used in a mix. It primarily adds volume, is good for drainage and aeration, but doesn't hold water. Keep that in mind when using it. Since Turface does hold water well, you may want to use more or less granite or Turface based on what you want the soil mix to do. If you want it to hold more water, use a bit more Turface. If you want it not to hold water, use a bit more granite or granite substitute.

Granite comes by many names. You might try a feed store and look for turkey grit, or find a masonry supply store and look for 1/16 silica sand. Also, you can try a construction supply and look for #8 or #16 silica. Lastly, a pool supply may use coarse silica in their filters, though one person recently wrote they are doing this less frequently and using glass instead, so this source may or may not work.

Gran-I-Grit is one names product you might find. You want "grower" or #2 cherrystone size.

Basically you are looking for something that is somewhere between 1/2 of a BB to a whole BB.

Oh, I forgot - above, perlite's function is to provide space between particles and do it in a lightweight way. It will break down over time. Also, it is very dusty. Use a mask when working with it to reduce lung irritation. You may want to water it down as soon as you open it to reduce the dust.

    Bookmark   July 14, 2009 at 9:20PM
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Peat is the last ingredient that is sometimes appropriate. Peat - which peat? People use terms like peat moss, sphagnum moss, sphagnum peat moss, reed and sedge peat, etc. So, which are we using?

You want sphagnum peat moss, sometimes called peat moss. You do not want anything called sphagnum moss or reed or sedge peat.

Peat moss holds water and is lightweight. It also is hydrophobic, meaning that once it loses most of it's water, it's hard to get wet again. It also compacts relatively quickly over time, breaking down into smaller particles which remove air space.

While you can use much more, limiting it to 10-15% of mixes used for plants that flower (including veggies), will help keep the mix from compacting and degrading too quickly.

Here is a link that might be useful:

    Bookmark   July 14, 2009 at 9:35PM
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Now that we have the ingredients, how are we using them? Your goal is to make a soil mix that works for your plants, allowing them maximum oxygen. But, as justaguy points out, sometimes that has to be tempered by our schedules. A mix that supplies maximum oxygen may require us to water more frequently that we are able.

So, we need to find a mix that we can live with, too.

Al's posts over the years have been to help people learn about how the the mix impacts your plants' health. He's offered some starting points you can use to get what you want. Along the way, justaguy has offered some counterpoint mixes that help the gardener who just can't water quite as frequently. We also have mixes that may be better suited to self-watering containers.

After I list the main options, I'll follow up at the end with some of the "rules" that you can use to help make your decisions.

    Bookmark   July 14, 2009 at 9:41PM
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Al's basic mix for short term plantings, things that will be there 1, no more than 2, years, is a 5:1:1.

5parts bark fines
1 part sphagnum peat moss
1 part perlite

The pH of this is usually around 5, but will depend on your sourced ingredients and if you needed to substitute something.

Al advocates changing this every year, unless you cannot afford to. This will decompose and compact over time, which will decrease the oxygen your plants get.

No more than 10% of the bark should be extremely fine if you are using peat. If you are not using peat, the percentage of extremely fine bark can be as high as 20%.

This mix is best for things that will die within the year, such as vegetables or annuals.

A mix for these same items in a self-watering container is listed in a later post.

    Bookmark   July 14, 2009 at 9:48PM
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I missed a material upthread (the joys of this archaic forum, lol). Al also uses bark - again, pine, fir or hemlock - in other mixes but not the fines that are listed above. These should be larger pieces.

This is better is it's not composted, whereas the fines should be partially composted. If I understand Al's posts, the size you want it what's shown at 9:00 on the picture below. The overall size should be between 1/16" and 3/8".

Here is a link that might be useful:

    Bookmark   July 14, 2009 at 11:53PM
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For longer term plantings, you want something that will last longer, not compact, provides great aeration, etc. This mix can be used for houseplants, woody plants, trees, herbs, etc. The pH of the mix is approximately 6.

1 part Turface or substitute
1 part bark (not fines)
1 part granite

If you need more water retention in this mix, use a bit more Turface and reduce the granite. If you need less water retention, decrease the Turface and increase the granite.

There are many similar mixes that can be made. For example, for houseplants, you could use a 2:1 Turface to bark, or a 3:2:1 Turface to bark to perlite. Whatever you decide, keep the organic material to 1/3 max of the total mix.

When you first switch a plant to a mix like this from a peat based mix, you may have to water twice a day. Eventually, it may need once a day or even every other day.

Here is a link that might be useful:

    Bookmark   July 15, 2009 at 12:19AM
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yellowthumb(5a Ontario)

Good summary, very helpful, even I read all the posts, there are still something I am not even aware of. thanks.

"When you first switch a plant to a mix like this from a peat based mix, you may have to water twice a day. Eventually, it may need once a day or even every other day. "

Why you have to water twice a day at first? Is it because the plant has not colonized all the soil yet?

    Bookmark   July 15, 2009 at 12:23AM
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In the original threads, several options came up for seed starting. The mix needs to be sterile, hold enough water without becoming soggy, and hold lots of air.

One method is to use screened Turface covered with 1/4" Turface fines.

A second is to use a 4:1 of screened Turface and chopped sphagnum moss. Sphagnum moss is different than peat moss. It's the stuff you often see used on hanging planters. It looks like dried moss!

Another option mentioned was a mixture of bark fines and Turface, but I didn't see a ratio.

The last option I saw was 5:1 NAPA Floor dry (make sure it's one of the floor dries that is fired and won't dissolve) and peat

    Bookmark   July 15, 2009 at 12:26AM
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Self watering containers are a bit different than regular containers. For the science and explanations of the WHY for all of these, read the original 8 threads with 150 posts each ;-).

Al listed two potential SWC mixes.

5 parts bark
2 to 3 parts peat
1 part perlite


5 parts bark
2 parts peat
1 part perlite
.5 part vermiculite

justaguy also tried several mixes through the course of the threads. He started with a 2:1:1 of bark, peat, Turface, but found this too fast (it dried out too quickly and he needed to water more frequently). Next, he listed a 3:2:1.5 of bark, peat, and perlite.

After some trial, he seemed to settle on the following:
4:1 bark (partially composted) to Turface. He doesn't use peat, but also points out this is NOT for a SWC using the EarthBox technology. This is for something that is both bottom and top watered and adding fertilizer through the waterings. If you are using EarthBox technology of having a covered top and the fertilizer inset, he found that he needed a 5:2:1 bark fines, peat and perlite to be successful.

    Bookmark   July 15, 2009 at 12:37AM
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yellowthumb, Al's word were, " until it gets its feet under it." And, thank you for the compliment.

    Bookmark   July 15, 2009 at 12:57AM
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Not sure how much longer I can stay awake, but thought I'd as some of the nuggets I pulled out of the threads, too.

The taller the containers, the denser the mix can be.

When bark water content drops below 35%, it's hard to rewet (same applies to peat).

A perched water table (PWT) is not a problem when the roots occupy the root zone. By then, they are large enough and thirsty enough to use the water. It's a problem when they are smaller and cannot colonize that area.

A 5:1:1 mix may drain too quickly in hot/dry areas.

Irregular, sharp edges of things like granite encourage finer rooting.

Wicks to drain a container are only to be used if the soil mix is less than optimal. If you are building your own mix, then build it so that a wick isn't needed.

When it takes 3 or more days in between watering (not sure how this applies if you are wick watering), it's too long in terms of optimal oxygenation.

    Bookmark   July 15, 2009 at 1:03AM
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Use 1/2 c of CRF (continual release fertilizer) per cu. ft of mix and 1/3-1/2 c of dolomite lime per cu. ft of mix.

A cubic foot is approximately 7.5 gallons.

A 50 pound bag of Gran-I-Grit is equal to 5.33 gallons.

Tilting a pot is a way to make the pot think the PWT (perched water table) is higher, so it will drain more quickly.

Particles sized 1/16" to 1/8" are ideal of inorganic mix items.

Particles sized 1/8" to 5/16" are better for bark (am imagining that fines are different, but not sure).

1/8 t of Epsom salts per gallon of water will provide Mg (magnesium).

Lime, at the rate of 3-5 pounds to 1 cu yard of soil, will raise pH .5-1 point. Also can use 1/3-1/2 cup per cu. ft or 1 T per gallon.

Gypsum will provide Ca (calcium) and will reduce pH.

Coir and peat have nearly identical water retention. Coir is easier to rewet. Coir breaks down a little faster. (I have read differently, but I won't say I know the truth. Below is one source that says different).

If you are using a soil mix that drains well, fertilize at 1/4 of the recommended rate at every watering.

Screens used to prevent insects from coming into your house can be used to cover holes in bottoms of pots to prevent soil mix from escaping. So can the needlepoint mesh sold at fabric stores.

Here is a link that might be useful: Source comparing peat to coir

    Bookmark   July 15, 2009 at 1:24AM
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This is an excellent summary. Thanks very much for building it. Obviously compiling 1000+ posts is no easy task.

This is great information, and I think many new container gardeners will benefit from it.

Thanks again.


    Bookmark   July 15, 2009 at 7:04AM
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rj_hythloday(8A VA)

About the Napa floor dry. It's part #8822 and is Calcined D.E. Just ask for kitty litter and look for the #8822 on the front of the bag, it's behind the counter. I paid $9 for a bag that's probably about a half yard, needs to be screened.

    Bookmark   July 15, 2009 at 2:03PM
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I tested my soil temp in my containers the other day with an old meat thermometer I have around the house and they seem to be between 80-90 degrees depending on the time of day.(I tested them about 3-4 inches into the soil around the base of the plant) Mine generally have sun for a great majority of the day other than when the sun is highest(awning gets in the way with my patio, no complaints as the Florida sun cooks them to much) and I have used light colored pots to insure they try to stay relatively cool. What is a good temp for soils in container gardens? I haven't seem this discussed to much.

Also, Does the different ingredients for soils impact temperature much. e.i using granite, more peat,less peat, etc, etc.

    Bookmark   July 15, 2009 at 3:21PM
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tapla (mid-MI z5b-6a)

Container soil temperatures should always be south of 90* or impaired root function is guaranteed on a very high % of plants. Best readings are taken between the container wall & the soil. Often, there is >30* difference between the soil there on the sunny side vs the shaded side.

The impact of the ingredients would be limited to their color (darker = greater solar gain if they are exposed to the sun), or to how much aeration they provide (well-aerated soils are cooler than compacted, soggy soils).


    Bookmark   July 15, 2009 at 6:18PM
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katskan, thank you. It wasn't so much hard, as time consuming. I had to do a bit of back and forth to make sure I wasn't misunderstanding anything.

I know when I first came here, I read part of one of the posts, but the info was so scattered, I found it hard. Everyone who's read them may forget just how much there is to wade through to get to the meaty parts. When I wanted to know more at a later date, I started taking notes at one point, and then figured I might as well post them for others.

I don't want anyone to miss the posts if they have the time and ability to get through them. On the other hand, it seems easier for Al and justaguy, who answer 99% of the questions, to not have to repeat themselves all the time, and for the readers to not have to spend literally hours to find the answer that they need.

I hope it fulfills that role.

    Bookmark   July 16, 2009 at 2:08AM
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yes taking the 1000+ posts on container soils and condensing them down to a brief, easy-to-read post is a great idea. Actually I started to do this a few months ago but I never finished it. I'm glad to see that someone took the time to do this. =)

Al and JaG have shared a wealth of information over the years and I've noticed that many time the same question is asked. Hopefully this post will eliminate at least some of those questions.

During the winter months, when there is nothing to do outside except watch it snow, I re-read all the "Container Soil" threads and I typically come across something I've missed. During the summer however, when free time is short, a condensed "quick reference" would be much easier to read.

So thanks for taking the time and thanks again to Al and JaG for sharing their knowledge with the group.


    Bookmark   July 16, 2009 at 8:28AM
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rj_hythloday(8A VA)

I grow almost entirely in raised beds, but have found a great wealth of info by reading the threads, this is a great resource before jumping into reading the full 1000+ posts (which I haven't finished)

    Bookmark   July 16, 2009 at 12:07PM
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Thank you for taking the time to consolidate so much of the information here for us. It will make it so much easier for me to find what I want when I need it. I did some of it myself at one time but there's still so much to read through and it's too easy to miss something important or to get confused.

    Bookmark   July 19, 2009 at 1:21PM
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Pieter zone 7/8 B.C.

Though I've been on GW for a while, my main focus is the Hosta forum and I only quite recently found this one. What a great idea to do this compilation, but, may I be so bold as to suggest this gets put into an FAQ so it will be easier to reference for newcomers to the forum?

    Bookmark   July 23, 2009 at 9:38PM
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I agree with kate and pietertje that compiling the 1000+ posts into a single, accessible thread is a great idea.

That FAQ idea sounds great as well!

    Bookmark   July 24, 2009 at 8:37AM
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I saw a product at Menards made by OilDri - it said it contained earth products - or something like that. So, I emailed. Here is their response:

The product purchased at Menards was our 25 lb Premium Floor Absorbent. It is a 100% Montmorillonite clay which we calcine at temps of 800+ degreeƂs. We sell a nearly identical product into agricultural markets so it will hold up well in water. If you need anything else please call or e-mail me. Thank you for your business.

Scott Hamming

Regional Manager

Industrial & Automotive Group

Oil-Dri Corporation of America

(800) 233-1959 ext. 2518

It sounds to me as if this *might* work. It's not fired as high as Turface, so may break down more quickly. But, I am not a specialist in any way. If, for some reason, you can't find the other products, consider this an option.

    Bookmark   July 30, 2009 at 1:16PM
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On the mixes discussed above....what type of plants could they used for or are they used specifically for certain plants

    Bookmark   August 23, 2009 at 5:53PM
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tapla (mid-MI z5b-6a)

Almost any plant will grow well in a highly aerated, fast draining mix. You may need to water a little more frequently, but minimal effort/grower convenience and the most robust plants often don't go hand in hand.


    Bookmark   August 23, 2009 at 8:03PM
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To lime, or not to lime, that IS the question :)

I've come across bits of information all over the place in this container forum and I've started losing track of what is what. I was under the impression that if I was going to use Foliage Pro that I wouldn't need to add lime to the mix, is that right? I hope it is, because I re potted all the house plants in a gritty mix and have newly potted a bunch of herbs and plants outside in the gritty mix, along with veggie's in a 5 parts fir bark, 2 parts Turface, 1 part pumice (a ratio I borrowed from Josh).

So can someone help me out here with the answer? And if I was supposed to add lime, now what do I do?


    Bookmark   April 12, 2011 at 12:27PM
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tapla (mid-MI z5b-6a)

The gritty mix would get gypsum as a Ca source if you are NOT using a fertilizer that has Ca (FP does).

If you are using gypsum in the gritty mix because your fertilizer doesn't contain Ca, it's also very likely it doesn't contain Mg, so for that reason, you'd want to also include small doses of Epsom salts (MgSO4) for the Mg, each time you fertilize (about 1/4 tsp/gallon of fertilizer solution.

When making your own soils that contain large fractions of conifer bark and/or peat, you should add limed at 1/3-1/2 cup per cu ft of soil.


    Bookmark   April 12, 2011 at 4:31PM
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hello all,
so i'm fairly new to all of this but have been lurking and learning thru all of your posts! thanks! I do have a question about al's 5-1-1 mix. Is there anyway to revitalize it for annuals for a second or third year? i absolutely hate throw out soil/mix. not only for cost sake although that is a factor, but for waste of non renewable resources. If not, could i compost it and use it in the raised beds?

thanks amyclaire

    Bookmark   May 1, 2011 at 9:07PM
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FWIW, I put the used up 5-1-1 mix in my raised beds all the time. Wherever that stuff is put outside, it benefits the plantings IMHO.

I don't even compost it. (Never had any problems at all, in fact, the plantings do very well in the raised beds doing this.)

But I do use compost every year and dig in autumn leaves every fall.

As to revitalizing the mix, I really don't know.

More knowledgeable members will have to answer that one.

For houseplants I use a more organic material in Al's gritty mix than he and other more knowledgeable members suggest, but it works very well for me.

But I don't want to give my somewhat bastardized recipe because it does run a bit contrary to Al's excellent recipe.

I'm an organic whacko so I tend to always use more organic matter and fertilizers in my houseplants. That is just me. Probably better to just do as Al suggests.

    Bookmark   June 5, 2011 at 8:43AM
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I just found this post by Al in another thread:

"Perlite BB-size to about aspirin or a little larger is good.

"I screen my peat into a rectangular mason's tub in a wheelbarrow through 1/2" screen to break up all the clumps & separate the big sticks, then I pour it into a 5 gallon bucket as a measure. It's dry & fully lofted when I measure.

"You CAN reuse the 5:1:1 mix if you wish, but ALL soils deteriorate at an accelerated pace as they age.

"For clarity, bark based soils break down at about 1/5-1/4 the rate of peat based soils on a particle size to particle size basis, but just because a soil breaks down at a rate slower than peat isn't reason enough to press it into service beyond it's ideal life.

"I'm pretty comfortable leaving plants in the 5:1:1 for 2 years.

"If I had to reuse, I would add maybe 3 parts of bark to 1 part of old soil, along with 1/2-1 part of perlite and a little lime."


    Bookmark   June 5, 2011 at 9:02AM
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matt_tampa(9a/9b Tampa FL)

"A 5:1:1 mix may drain too quickly in hot/dry areas."
Has this not been a problem in areas that are hot and humid? Is there an adjustment to the formula that would make it stay wet for longer?

I haven't seen any actual instructions for making the mix - does the bark need to be moistened beforehand? How would one do that? I also saw someone make a reference to letting the mix sit around for about 2 weeks if using uncomposted bark fines - is this to allow it to start decomposing?

"Perlite BB-size to about aspirin or a little larger is good."
So this is not the normal perlite that I find at Lowe's or HD. Will the smaller perlite not work in the 511 mix? Are any of the perlite alternatives - Turface, pumice, etc. - actually commonly available at stores?

I have a bunch of store-bought potting mix that I need to use up, so I was going to use it in the 511 instead of peat. The potting mix's ingredients are listed as: 55% - 65% aged composted pine bark, followed by spaghnum peat. The mix feels to the touch more or less like normal potting soil, with just a few larger chunks mixed in. Should I assume that this mix will have the same drainage characteristics as pure spaghnum peat, or else how could I adjust the formula?

What is the typical pH of pine bark and of peat? I'm assuming that my potting mix is pH neutral, so if I'm using that instead of peat, but still using 5/7 pine bark fines, would I need to add the same amount of lime?

At the landscape supply store where I found a great deal on bark fines, I asked if they had dolomite lime, and the guy gave me a bag of "horticultural hydrated lime," which I assumed was the same thing. Now I see that it apparently is not. Can I still use the stuff I got, or should I return it?

I have some organic fertilizer that has N-P-K of 3-4-4. It also has 5% calcium and 1% magnesium. If I'm using this, will that be sufficient Ca and Mg that I don't need to further supplement? I also got some bat guano and some powdered seaweed, so I can add more of one macronutrient to the balanced fertilizer.

Many thanks to Al, Lathyrus, and everyone else who has contributed on this forum.

I also like the idea of making this an FAQ - it would make it much easier to use as a reference. And why does this site have such archaic software? Especially considering that there is excellent modern BB software that's 100% free. It would certainly make the forums a lot easier to use.

    Bookmark   July 11, 2011 at 2:54AM
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