QUESTION: How do I know when my compost is ready? It looks sort of like it is, but I’m not sure. – Alex T
ANSWER: You can tell when your compost has finished working by checking its temperature or simply inspecting the compost. It isn’t possible to reliably estimate when compost will be finished because the timeline can vary depending on your balance of ingredients, the size of your materials, the frequency at which you turned the compost, how often you added items to the compost bin, and other factors. The process of transforming from raw materials to mature compost can take anywhere from one month to a year.
When compost has finished its process of decomposition, it will resemble soft, crumbly soil, and you will not be able to identify the ingredients that went into making it. (However, there may be a twig or other item that was tough for the microbes to break down here or there, so consider the overall product.) When compost has finished its process of decay, it will be dark in color: between a very dark brown and black.
Give your compost a sniff, too—when it’s finished and ready to use, it will smell like very fertile and rich soil. This is a pleasant smell, so if you’re catching an aroma similar to ammonia or a rotten or musty smell, your compost has not finished decomposing (and it also needs some tweaking as far as the balance of materials, the moisture level needs adjusting, or it simply needs to be aerated by being turned). And when it’s finished, your compost pile will have decreased in size by about half due to decomposition.
If you’ve been monitoring the temperature of your compost, you’ll notice it drops significantly when the compost is ready to use. That’s because there’s no more work for the microbes to do breaking things down, and their efforts are what generates the heat in your compost.
Even if you haven’t been tracking the temperature of your compost pile, you’ll notice when it’s complete that the compost is not warm to the touch. It may even be cool enough for some of your backyard earthworms to have moved in. When the compost pile is active, the temperature is too high for earthworms to be comfortable, especially near the center of the pile.
It’s important that you wait for compost to be complete and ready to use before putting it to work in your garden for several reasons. One, before the compost is complete, it’s possible that it could harbor plant diseases or parasites that could be passed along to your garden plants.
Half-finished compost can even burn your plants, not in the way that too strong a dose of fertilizer can do, but with the heat the compost generates when it’s working.
If you still aren’t certain whether your compost is ready to use, it may help to review the compost maturity tests available at the University of Florida Extension’s website [http://sfyl.ifas.ufl.edu/sarasota/natural-resources/waste-reduction/composting/what-is-composting/when-is-compost-ready/compost-maturity-test/]