First post here. I recently heard that you can use comfrey, yarrow, or nettles to activate a compost pile or biochar. I am assuming this is because the plants attract beneficial microbes when they decay. Does anyone have a more in-depth explanation on this? Why do only certain plants have this property?
Ben Stallings wrote:I'm not able to answer this question, but I had thought it had more to do with nutrient content -- these plants are like multivitamins for the decomposers. I would add giant ragweed (Ambrosia trifida) to the list -- it breaks down exceptionally quickly and cleanly in a sheet mulch or compost environment.
Good point. So perhaps plants that activate compost/biochar are ones that breakdown quick and release lots of nutrients.
Tony Gurnoe wrote:I'm not sure I really understand what you mean by "activate" a compost pile or biochar. If you're referring to inoculation I don't see what any of those three plants would offer that others wouldn't. It's worth mentioning that the beneficial microbes are the ones that cause the decay of this material rather than microbes coming in after the fact. Comfrey is famed as a biodynamic accumulator and biomass producer. The deep roots of the comfrey plant draw nutrients from deeper in the soil than many plants can access. When the leaves are chopped and used as mulch, which can be done several times in a growing season, they decompose quickly returning these nutrients to the topsoil besides all of the benefits of an organic mulch. Nettles are similar but they're especially adept at accumulating nitrogen in the form of proteins. Dry nettle leaves by weight contain some of the highest levels of protein of any edible leafy greens. This is part of why nettle leaves are so healthy for us to eat. As these proteins break down in the soil the nitrogen that was stored within is released for the plants' roots to take in. Yarrow is a great plant in its own right. It will grow in poor dry soil, has medicinal uses, and attracts beneficial insects.
Thanks Tony. I don't exactly understand what it means to activate either. I just hear of the people doing it! In the case of compost, if you are starting a compost pile where there is no current healthy soil or existing compost, maybe these plants can quickly cause the growth of healthy microbes in your pile increasing decomposition. In the case of biochar, I think the idea is that you want to somehow cover all that new surface area created with beneficial microbes before you put it in your soil increasing its potency.
geoff lawton in the PDC video with him and Mollison lists certain things as being compost activators: comfrey, nettles, yarrow, fish, or a dead animal.