Wood Ash in Compost
December 21, 2019
Hello, is it ok to put wood ash in our compost? We’ve read numerous sources online that say it could be beneficial, depending on your soil ph. But we noticed in your flyer, “Composting in the Desert” that we should avoid it. Could you explain further?
We’re just starting our first compost bin. Our zip code is 87043. Our setup is a homemade 40-gallon plastic bin with holes drilled near the bottom. We decided to start with the cold pile method since that seems easier. Your flyer has been very helpful is getting us started!
Looking forward to your response. Thanks in advance!
Answer by JH: Thank you for your question. You may also receive responses from other master composters. Following are my thoughts. Generally the soils in our area are 7 pH which is neutral. It would only be appropriate to add ash to acidic soil (below 7). Even so, there is no benefit to putting ash in compost - it does not aid the process and may well slow it down if it retains moisture that would otherwise saturate the decomposing feedstock in the pile. Following are two links to more detail about the soil in your area.
For more instruction about desert composting feel free to attend any of the classes we offer. The schedule is posted on our website.
Answer by JZ: Great to hear that you are getting started and that our brochure has been helpful.
Here are my thoughts in addition to JH's. Wood ash is considered to be alkaline AND it does contain potash (potassium), calcium and other residual nutrients which would end up in your finished compost. Wood ash is a “low grade” fertilizer, best applied to an acidic soil because of its high pH. Our local soils are often alkaline - high pH, because we do not get enough rainfall to wash the bases (alkalinity) downward - they just sit there. I live in Rio Rancho where my native, unamended soil pH is 8 - alkaline. Some think that the alkalinity of wood ash will carry thru the process and make the finished compost alkaline. The decomposition (composting) process is a neutralizing process, that is, the end product (humus) will be neutral pH. Unless, of course you overload the system
with an organic material which highly alkaline or highly acidic. I think that if you applied small amounts of wood ash (one cup) every now and then and blended it in with the top layer of greens & browns, then you would not overly alkalinize your compost bin contents. I would use wood ash sparingly and prudently in my composting setup - if I had some. Wood ash might also be spread lightly in areas where local desert plants are growing and / or on a gravel driveway, where nothing is growing.
So the decision is yours to do what you think is prudent. Hope that this is helpful. All the best.
From original questioner: Thanks JH and JZ, for your detailed responses! You've been very helpful. We don’t have a lot of ash so I think we’ll probably just scatter it on our driveway, maybe add a small amount to the compost. Not sure if it makes any difference but we do drink a ton of coffee! And coffee grounds make up more than the recommended ratio of our bin. Perhaps the alkalinity of the ash would offset that acidity a little? Or would any effect be negligible after the neutralizing process?
Anyway, thanks again!
Answer by JZ: Thanks for your response. Yes, the coffee grounds which are Ph 6.5 would help offset the alkalinity of wood ash a little. Blend them together, then add. As mentioned, just add small amounts of ash occasionally, the rest goes to your driveway. The ash is mostly inorganic so in general it is not decomposed, but the residual nutrients will end up in the finished compost.
Other sources of browns (carbon) would be now abundant leaves and used household paper products - paper towels, napkins, egg cartons, shredded paper, filters.
Wood ash is much discussed with reference to garden soil / composting so when you have time do a search “ wood ash in compost & garden” I think that you will find some helpful information.
Composting is a dynamic transformative process. Think that you will be pleased with the end result, so keep up.
You and family would be welcome to register then attend any of our classes as often as you wish. See Classes under Activities in our website menu. All the best.
Answer by JH: I’ll defer to JZ on the quesrion about coffee grounds/wood ash. Personally, I load up my compost with coffee grounds because they are an excellent source of nitrogen and free at your local coffee shop. I personally wouldn’t worry about having too much of it unless it overwhelms the carbon contents.