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Liquid Fert in a self-watering container?

Posted by jethrojames 7 Raleigh, NC (My Page) on
Thu, May 8, 08 at 18:02

Hello all!

I am thinking of trying something different this year with my self watering containers. I was thinking of using a diluted liquid fertilizer to feed the containers, instead of the usual fertilizing options (fertilizer strip or slow release pellets). The idea comes from the paper linked below.

Has this been tired by anyone here (I did do a search before posting), and if so, perhaps some suggestions on the strength of the mixture. I know Miracle-Gro suggests 1 tablespoon to every gallon, but from reading the above paper, it sounds like the dilution would be much lower, perhaps 1 tablespoon per 4 or 5 gallons.

Thanks for any help or suggestions!

Here is a link that might be useful: Simple noncirculating hydroponic method


Follow-Up Postings:

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RE: Liquid Fert in a self-watering container?

The method you linked to is very different from using a liquid fert in a self watering container. In the method you linked to the plant grows in a non recirculating nutrient solution. In such a case you would dilute the fert because as the plant draws up water, the salts from the fertilizer concentrate in the remaining water.

In a self watering container the water will wick into the potting mix and the water levels are topped up frequently diluting the salts. The SWC can also be flushed by overfilling the reservoir to remove excess salt build up (not usually a problem over a season).

For a SWC just mix a gallon (or whatever amount you need) full strength and add to the reservoir (or right into the mix) and be done with it. I wouldn't suggest doing this more than once or twice a month unless your plants indicate otherwise. There is nowhere for those nutrients to go in a SWC so they remain there until the plant uses them. In a traditional container some are flushed out with each watering.

Does that help at all?


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RE: Liquid Fert in a self-watering container?

Hello justaguy!

Thanks for your reply! Yes, it was very helpful, but I think I need to explain my setup in more detail to see if I am going to have a problem.

I have a self watering container that has a reservoir that has it level maintained by a float valve (a design of my own; not an EB design). The float valve is currently hooked into a water faucet, so I never have to fill the reservoir by hand. Feeding is done my adding some Miracle-Gro by hand, as needed, which is usually about once a week when the plants get bigger and start to fruit.

My idea was to setup a 35 gallon garbage can, as described in the article, and then gravity feed my float valves with the water/fertilizer from the garbage can (instead of from the faucet). I have to check out the gravity feed side of things (it should not be a problem), but my concern was with how much fertilizer to put in the water?

You mentioned salt build up (was not aware of this; thanks!). If the containers were not covered, would the occasional rain shower be enough to wash the salts out? (BTW, the reservoir does not cover the entire bottom of the container, so I have a drain hole for any excess water to drain out) If the container was covered (as in an EB), would their be a salt build up problem?

Thanks again for your insight, and hope you can help me with some of the details of my idea.

Thanks!


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RE: Liquid Fert in a self-watering container?

It all depends on how frequently you will add water to the nutrient solution. By definition any time you add water with fertilizer to a container we are adding a nutrient solution.

If we will add nutrient solution only once (as in the linked example) then we have to be aware that as the water volume is consumed by the plant the fertilizer will leave salts behind which become increasingly concentrated as water volume decreases.

If we add nutrients to a water supply that will be continually topped off with fresh water (no nutrients) then the build up of salts isn't of much concern as it remains continually diluted to safe levels unless we over fertilize to an extreme.

In your case you have a SWC with an auto top off unit so the salts in the water will never concentrate as long as you don't go nuts with the fertilizer. At the end of the season run water through the growing media from the top and overflow the water reservoir awhile. This will flush much of the accumulating salts and make things a non issue for the following year.

How much fert to use? Pretend you aren't using a SWC. If you were using a regular, top watered container you might use a full strength dilution once every couple weeks. Or you might go half strength every week. It all works well enough. The only thing to consider is that in a SWC application there is no drain hole for the excess to run out so be a tad more conservative with the fertilizer as it has no drain hole to run out of.

Over the course of a single season though it is very unlikely you will have enough salt build up to cause problems so don't worry too much about it.

If you were to go with the example in your link then I would suggest a 1/4-1/3 strength dilution since the water could be used until only 25% were left and this would only result in a normal dilution rate.

What you are doing though offers more flexibility and you can just flush the system at the end of each season to stay safe.

If you are looking for a hard and fast recommendation then refill the reservoir every 2 weeks with a half strength dilution and watch the plants. If they show no signs of nutrient deficiency (unlikely) then don't deviate. If they do, then adjust accordingly.


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RE: Liquid Fert in a self-watering container?

Hello justaguy!

In your case you have a SWC with an auto top off unit so the salts in the water will never concentrate as long as you don't go nuts with the fertilizer. At the end of the season run water through the growing media from the top and overflow the water reservoir awhile. This will flush much of the accumulating salts and make things a non issue for the following year.

Over the course of a single season though it is very unlikely you will have enough salt build up to cause problems so don't worry too much about it.

Thanks! This is what I was thinking, but needed someone with some experience to tell me I was on the right track.

If you were to go with the example in your link then I would suggest a 1/4-1/3 strength dilution since the water could be used until only 25% were left and this would only result in a normal dilution rate.

Actually I would think that as the solution gets drawn out of the garbage can, the solution dilution would stay the same, unless some water is evaporating off, or if I add some water with out adding some fertilizer.

The plan right now is to make a full mixture, and when it gets half empty, I will fill it back up with water, and add half the original amount of fertilizer. And will probably go with a very light concentration rate that is suggested by Miracle-Gro, probably something as low as 1/10. That way if it is too light, I can go up.

Thanks again for helping out. I will post back with any updates as the growing season goes along.


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RE: Liquid Fert in a self-watering container?

Actually I would think that as the solution gets drawn out of the garbage can, the solution dilution would stay the same,

Not necessarily. Salts are good for plants, they are the nutrients they use, but they can also accumulate on the growing media as well as on the roots of plants or in the case of ceramic pots, on the exterior. In a closed system management of salt levels becomes important as they have nowhere to go unless the plant uses them before they settle onto something like the container, the roots etc.

Other than this nit pick, I think you have a well thought out plan and suspect you will have great results this season.

Please do post back with what you did and how it worked out. If possible include some pics as I love seeing pictures :-)


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RE: Liquid Fert in a self-watering container?

Hello justaguy!

Yes, I will post some pics when I get it done.

One final question: Which water soluble Miracle-Gro formula do you think I should use, the General Purpose (24-8-16) or the Tomato Plant Food (18-18-21)?? Or perhaps you have a different suggestion? I am growing Sweet 100 cherry tomato, a grape tomato variety, California Wonder green pepper, Kentucky Wonder pole beans, and Clemson Spineless okra. I may also use it to feed a Triple Crown blackberry bush, but that can be feed by hand.

Thanks as always!


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RE: Liquid Fert in a self-watering container?

That is actually a somewhat difficult question for me to answer because my understanding of tomato nutrient requirements has changed recently as I have looked at the results of tissue analysis done on plants growing and producing well.

Previously if I had to choose between those 2 I would have chosen the 18-18-21 in order to avoid having nitrogen be the highest number. The only thing I wouldn't like about that ratio is the phosphorous is present in exponentially higher than needed amounts.

My plans for this year are to use a 3-1-2 ratio (which is what the 24-8-16 is) for nearly everything including tomatos. I will also be using a 0-0-3 in combination to boost the K where it makes sense to do so.

Using tissue analysis to indicate what tomatos need and when, here is how it breaks down:

From seedling to 5 leaf stage:
(N 3 to 5) (P 0.3-0.6) (K 3 to 5)

From 5 leaf stage to first flower:
(N 2.8-4) (P 0.2-0.4) (K 2.5-4)

During early fruit set:
(N 2.5-4) (P 0.2-0.4) (K 2.5-4)

At the first ripe fruit:
(N 2-3.5) (P 0.2-0.4) (K 2-4)

Harvest period:
(N 2-3) (P 0.2-0.4) (K 1.5-2.5)

Notice the trend here. Pretty much the entire life cycle the tomato performs best with fairly even amounts of N and K and very little (relatively speaking) P. Having the N a little higher than the K seems to be what the plants actually want (though only a tiny amount higher).

To be honest with you I don't know which is going to work better for you and I think either will produce acceptable results.

Something to be aware of is that tomatos (and many other plants) will use more calcium, magnesium and sulfur than they will phosphorus so make sure you are providing those as well for best growth. The MG won't have them.

Lastly, I recently posted this, which is meant to assist veggy growers in making their own determinations as to 'what is the best fertilizer'. I think you will find the information beneficial.


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RE: Liquid Fert in a self-watering container?

Hello justaguy!

Thanks for the info. I did notice your previous post about the tissue analysis; interesting reading. I will have to see if the state offers this service. They have the soil analysis for free.

Digging a little deeper on the continuous watering/feeding problem, the Miracle-Gro website had this measure for a continues feeding method:

Constant feeding method: 1/4 teaspoon per gallon of water, given at every watering.

Wow!! That is like a 1/12 mixture, much lower than both of our guesses! I will go with their recommendation for now, and see what the results are.

Hyponex potting soil: Well, I guess I am the exception to the rule. I used this exact brand of potting soil last year, and had fine results. In previous years, I have used other off brands that were half the price of the the name brands, and have had great results. In fact, I was a little irritated at the Big Orange Store for not carrying the cheaper, off brands this year. I went to Wally World to get my soil this year. Maybe I got lucky, but I will let you know how it turns out.

Thanks as always!


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RE: Liquid Fert in a self-watering container?

Interesting they recomend a 1/12 mixture. I think you are right to follow their recommendation though. You can always adjust.


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RE: Liquid Fert in a self-watering container?

Hello.

I finally got my continuous water/feeding system setup, and it looks like it is working fine.

I got a 35 gallon Rubbermaid trash can, filled it with water, and added 3 tablespoons of Miracle Gro to the water (~1/10 mixture). At first, I looked at adding a water spigot to the bottom of the trash can to feed the containers. But in the end, all I did was to use a drip emitter punch and used a coupler to hook it up to some 1/4" drip emitter tubing. Here is a photo:

Image Hosted by ImageShack.us

Next, I had to hook the 1/4" drip emitter tubing to the 5/8" hose that was feeding the containers. The solution was to use a 5/8" spigot to 1/4" adapter (black) to a Y valve (yellow; use this as a shut off valve) to a female-to-female adapter (brass) to the hose. Here is a photo of the details:

Image Hosted by ImageShack.us

Since I already had the hose, Y valve, barbs, 1/4" hosing, and hose adpater, the only thing I need to purchase was the garbage can and the female-female adapter, less than $10 for both. If you had to buy everything new, probably around $20.

So far, so good. No leaks so far (the leak in the first photo was due to me pulling on the line for the photo; it is fixed now.) Going from a 1/4" tubing to a 5/8" hose is not going to be a problem. The flow in the system is low enough that I will not get much of a pressure drop going from a smaller to a larger hose diameter. Also, I have about 2 to 2-1/2 feet of head, so pressure should not be a problem either. Going forward, I am going to try and keep the concentration of 1 tablespoon per 10 gallons of water. If it looks like the plants need some more food, I will try and up the concentration.

So, there it is! If I change the system at all, I will post an update here.

Questions and comments are welcome!

Thanks!


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RE: Liquid Fert in a self-watering container?

looks good. Can you do a full set up pic?


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RE: Liquid Fert in a self-watering container?

Here are few more photos to help show the setup.

I have the 35 gallon trash can up on a couple cinder blocks on the deck.

Image Hosted by ImageShack.us

Right below the deck, I have the adapters and valve described above.

Image Hosted by ImageShack.us

At the end of the hose, I go to 1/2" drip emitter hosing. From there, I have 1/4" tubing that feeds the automatic irrigation device.

Image Hosted by ImageShack.us

I was thinking about it, and this setup might also work with the Earthbox automatic irrigation setup. But since I do not know the details of how it works, I could not tell you. Does anyone know if the EB automatic irrigations setup will work on a gravity feed?

Hope these picture help describe the setup in better detail.

Thanks!


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RE: Liquid Fert in a self-watering container?

Does anyone know if the EB automatic irrigations setup will work on a gravity feed?

Nope. They are designed to operate under, I believe, 10lbs of pressure which while very low PSI is more than most gravity feed systems provide.

Regardless it seems there are more on this forum (posters anyway) using homemade SWC than commercial EBs so your set up, if it works well for the season, should be helpful to many.


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