3 ways to tell homemade compost is ready to spread

Q uestion: I set up a box-like compost bin last fall and started adding leaves, plant materials and kitchen scraps to it a few days later. I’ve been adding more to it throughout the gardening season and turning it occasionally. How do I know when the compost is finished and ready to spread? Are there any areas of the garden where I shouldn’t add it?

Answer: Kudos to you for setting up a home compost pile and using it to recycle materials that would otherwise end up in a landfill. It sounds like you have a good mixture of materials going into your pile, which means you’re off to a great start. Exactly when your compost is ready to “harvest” depends on a few different factors.

For the fastest decomposition, you should aim to have about 2-3 times more “brown” materials going into your pile than “green” materials. Browns include carbon-rich ingredients like autumn leaves, straw, shredded newspapers, unbleached paper towels, etc. Green materials are high in nitrogen and include such items as untreated glass clippings, plant trimmings, farm animal manures, and spent plants. This ratio feeds the microbes that break down your pile a balanced diet and encourages them to work at a rapid pace. It also keeps the pile from becoming too wet and hot.

Other than the balance of materials, another thing that determines how fast compost decomposes is how frequently it’s turned. If a compost pile isn’t aerated via the turning process once or twice a month, the decomposition process will switch from aerobic to anaerobic. It’s a whole host of different microbes for anaerobic decomposition and it takes a good bit longer for them to fully break down the materials. If you don’t regularly turn the pile it’s called “cold composting.” Yes, you’ll eventually get finished compost, but the process will take a long time and the balance of carbon to nitrogen in the finished compost may be less than ideal for supporting plant growth. You may also have trouble with odors or wetness in your pile.

A third factor that determines how fast finished compost is produced is the particle size of the original ingredients. Large plant stems, small twigs and whole leaves take a lot longer to break down than materials that have been shredded prior to adding them to the pile. Smaller particle sizes mean more rapid decomposition.

Also, since you’ve been adding new materials to the bin throughout the gardening season, that will affect the speed of decomposition as well. Ideally, you should have two bins. Fill up the first bin with the proper ratio of “browns” to “greens” and then stop adding new materials to it. Turn that first bin a few times a month until the compost is ready to harvest, and only add new materials to the second bin. By the time the second bin is full, it’s likely that the compost in the first bin is finished and ready to spread in the garden. Rotating between the two bins is a great system to ensure a good supply of finished compost.

I can’t tell you exactly when your compost is ready to spread due to all of these factors, but I can tell you what signs to be on the lookout for that will tell you the decomposition process is complete.

1. The original ingredients are unrecognizable. Finished compost should be brown and crumbly. You should not be able to see any recognizable stems, leaves or other materials in the compost.

2. Finished compost smells good. The fragrance of your pile should be earthy and fresh. It should not smell musty or ammonia-like (if you smell those odors, it could be a sign that you aren’t turning the pile often enough or that your ratio of ingredients is off.)

2. Your compost should not be hot to the touch. The process of decomposition generates heat, so “working” compost piles are steaming hot. But, when the composting process is complete, the temperature of the pile drops significantly. The presence of earthworms is another indicator that the process is complete. Worms cannot survive the hot temperatures of a “working” compost pile and they will only move in when the process is near completion.

As for where to spread your compost, if it’s finished, you can use it anywhere. I spread mine around my perennials and in my vegetable garden. I also use it in my strawberry patch. The only caution I’d like to make is to be careful where you use your compost if you’ve added weeds to it that have gone to seed. Most home compost piles don’t reach a high enough temperature to kill weed seeds. For that reason I suggest keeping weeds that have gone to seed out of your compost bin to save yourself some headaches in years to come.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.