Can you grow plants in pure compost?

californianMarch 5, 2009

I was thinking of planting all my garden in 5 gallon containers, or bigger if I can get them cheap. The cheapest stuff I can buy to fill the containers is pure compost, which I can buy for $8 a cubic yard, really nice stuff made from horse manure and sawdust, completely composted and fine screened. Sand would cost around $45 a cubic yard plus an equal amount for delivery. I used to be able to get perlite for $2 a cubic foot, but the place I got it from isn't answering the phone so probably went out of business, and any other sources charge too much so perlite is out. Vermiculite has gotten very expensive because of the asbestos issue so that is out too. Actually there is something cheaper I could use, which is my almost pure clay soil, so pure I could make pottery or bricks from it.

I read that squash can grow in a compost pile, has anyone ever grown anything in pure compost with nothing else added to it, and how did it turn out? What about mixing clay and compost say half and half?

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tapla (mid-MI z5b-6a)

You might be able to get away with growing in some mix of compost and very coarse sand (1/2 BB size to BB size) if the fines are screened out of the sand, but pure compost or a mix of compost and fine sand will present compaction/water retention issues that would be very difficult to get around. If you decide to try it, sinking the containers into the soil so the drain holes are buried might help employ the native soil as a wick; but, if the soil is as you described (clay) that may not help much either.

Vermiculite wouldn't be the choice for a compost based soil because you already need to be VERY concerned about water retention. Stay away from sawdust - rapid breakdown and soil collapse - nitrogen immobilization.

Pine bark is cheap - why not use it?


    Bookmark   March 5, 2009 at 8:18AM
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I have grown in pure compost in containers. It works, but I don't recommend it. It continues to deteriorate and you'll have a lot of shrinkage in the container. It tends to hold moisture more than is good for a container. If you can mix it with other things, making your own potting soil, that would be best.

    Bookmark   March 5, 2009 at 10:07AM
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Using pure compost, clay soil, or any mixture of the two alone as a container mix will likely cause a drainage issue. You should add some kind of drainage material or sink the containers as tapla suggested. Additionally, growing with an excessive amount of organic matter can create high levels of nitrogen which can result in excessive, spindly vegetative growth and reduced flowering.

    Bookmark   March 7, 2009 at 10:44PM
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