While the compost piles here in Minnesota are frozen solid and buried under a couple of feet of snow now, it’s fun to imagine the time when they will begin churning and decomposing and creating delightful humus for the garden. And, after the Master Gardener training class on soils and composting, I have a better idea of how compost works and how to get compost quicker. University of Minnesota professor Carl Rosen led the class, which covered everything from what soil tests measure to how to improve your soil’s fertility: basically, add compost.
Here are six tips from Rosen on making compost.
The optimum size for a compost pile is 4 feet by 4 feet by 4 feet. At those dimensions, the compost will heat up quicker and decompose faster. That said, compost happens, almost no matter what you do. If your pile is smaller, it will take longer for the leaves, grass clippings, and vegetable waste in the pile to decompose (think years, not months), but it will decompose eventually.
- Compost starter is not necessary. Most compost starters provide microbes and nitrogen to get the material you are composting going. While microorganisms and nitrogen are needed for compost to get started, you can add a couple of shovels of garden soil and maybe a handful of fertilizer to get the same benefits at a much lower cost.
- Compost piles like shade. While you can make compost anywhere, Rosen likes shady locations because they protect the pile from drying winds and sunlight, which also dries the compost out and slows the process. Another factor to consider in placing compost bins are the bins’ impact on neighbors—compost that stinks (it shouldn’t) or obstructs a neighbor’s view probably isn’t going to make you the most popular person on the block. Consideration is always a virtue.
- Add air. Most gardeners know that to make compost you need brown materials (dried leaves, etc.), green materials (plant debris, grass, vegetable peelings), and moisture. But you also need air. You can add air by turning your pile or by adding bulkier items. If you want to add air with bulky materials, Rosen recommends wood chips, which keep air in the pile because of the spaces around the chips. The only disadvantage of wood chips is that you will need to sift your compost through a screen to get them out.
- Is it done yet? When your compost pile is finished, it should be about half the original volume of the pile and have an earthy smell. A well-managed compost pile will be ready in 4 to 9 months. A poorly managed pile will take 1 to 3 years, according to Rosen.
- Gardens need compost! While not exactly news, it’s important to recognize how many ways compost benefits gardens. To improve fertility and tilth, add 1 to 2 inches to the top of the soil and work it in 6 to 8 inches, if possible. Compost also makes a great mulch — you need 2 to 4 inches to suppress weeds — and it’s a wonderful amendment to potting soil for containers. Make compost 30 percent of the volume of soil in your containers for healthy plantings.
One other note from Rosen: Compost piles in frigid climates (like Minnesota’s) are dormant in winter. Another reason to hope for spring.