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Because of limited space for gardening, we have a fairly large number of trees and plants in flower pots. In particular I have found that citrus trees seem to demand a lot of mulch around them and so I am doing sheet mulch and in place composting in the pots. There is usually a 2-4 inch layer of leaf fall mulch covering a thin layer of kitchen waste in these pots. The leaf fall is currently mostly mango and papaya leaves. The mango leaves are usually green when put in, the papaya leaves may be harvested when the show that they are about to fade. I would assume most of this would be considered a "green" for composting purposes and that the soil and plant acts as the main nitrogen sink. Sometimes I add mango twigs as a brown, however.

I would also like to add that most pots contain between one and three different plant species. Examples include lemon and ginseng, eggplant and ginseng, some sort of sour starfruit relative, celery, and ginseng, eggplant, lime, and durian, and the so forth (yes I am growing a lot of ginseng-- I have almost 20 ginseng plants and counting, most of which are only a few months old).

My question is this. When composting above-ground parts of plants in an area where there is not much topsoil, such as a flower pot, to what extent do I need to worry about allelopathy between plant species? Is this a serious issue I need to keep a close eye on? Or is it less of an issue since typically I am not dealing with a lot of roots?

  • I have some doubts whether allelopathy is a topic that fits well on this site but I'm curious to what other people think. Nevertheless I think it is an interesting question so I'm going to answer it anyway. – THelper Apr 25 '13 at 10:18
  • The overall question is whether I need to worry about allelopathy when composting in place. If it was planting together I'd ask on gardening. – Chris Travers Apr 25 '13 at 10:19
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AFAIK most occurances of allelopathy indeed come from roots, but it is possible for allelopathy to occur from allelochemicals leaching from leaves via rainfall or from fallen leaves. For example the leaves and nuts of the black walnut inhibit growth of plants like tomato, pepper, and eggplant. Composting it first separately (so not directly composting in pot) will reduce the amount of allelochemicals, but may not remove it entirely.

I've never found a good list or guide on allelopathic plants and trees and suspect a lot of this is still unknown. I did a quick google on the plants you mentioned and here is the result:

  • Mango: dried mango leaf powder completely inhibited sprouting of purple nut sedge tubers (source)
  • Papaya: papaya seed reduces the emergence of seedlings from certain plants like tomatoes and cucumber (source)
  • Citrus tree: no replanting of same sort (source)
  • Ginseng: no replanting of same sort (source)
  • Eggplant: found nothing.
  • Celery: inhibits growth of lettuce (source)
  • Durian: found nothing.

It looks like you are ok with the mango and papaya leaves, but you may want to do a more extensive search that includes the latin names of your plants.

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