Compost microorganisms need both carbon and nitrogen to survive. Carbon serves as a food source, while they use nitrogen to build proteins and reproduce. (See References 1, page 6) While you don't need to maintain a precise balance of carbon and nitrogen in your compost pile, providing adequate supplies of both will produce compost faster. However, you may occasionally end up with bulk amounts of carbon- or nitrogen-rich wastes. Gardeners use compost activators when composting large quantities of high-carbon materials.
Definition and Purpose
Compost that breaks down slowly often lacks nitrogen, the most common limiting nutrient in the compost pile. Compost activators jump-start the composting process by providing a missing nutrient, usually nitrogen, needed by the microbes in the pile. Compost activators help break down materials high in carbon but low in nitrogen, like the large amounts of fallen leaves collected in the autumn. (See References 1, pages 17-18)
How Much to Add
The Cornell Waste Management Institute recommends adding .15 lbs. of actual nitrogen for every 3 bushels or 4 cubic feet of dry leaves. Because different nitrogen fertilizers contain different amounts of nitrogen, the amount of fertilizer to add as an activator depends on the type you're using. Urea requires the lowest application rate: only 5.2 oz., or less than 1 cup. Ammonium nitrate requires 7 oz., or about 1 cup. You'll need to add 1 qt. of calcium nitrate. The organic nitrogen fertilizers blood meal and fish meal require 1 1/4 qt. and 1 1/2 qt., respectively. Add the compost activator to water and mix it in well. As you build your compost pile, sprinkle the liquid activator between the layers to ensure a supply of nitrogen throughout. (See References 1, page 18)
Garden catalogs may recommend the purchase of a compost activator when starting a new compost pile. However, unless you're intending to compost only high-carbon materials, you won't need a compost activator, according to the Cornell Waste Management Institute (see References 2) "Green" ingredients like food scraps and grass clippings will supply adequate nitrogen for microbes to thrive (see References 3).
Compost inoculators are another compost additive and easily confused with activators. Compost inoculators add microbes to your compost pile, not nutrients. However, since these microbes occur naturally in the materials you use to compost, adding more doesn't benefit your compost. If you want to increase microbial populations, a handful of garden soil or finished compost will do the job as well as commercially available inoculators. (See References 2)
First published in 2000, Dawn Walls-Thumma has served as an editor for "Bartleby" and "Antithesis Common" literary magazines. Walls-Thumma writes about education, gardening and sustainable living. She holds a Bachelor of Arts in psychology and writing from University of Maryland and is a graduate student in humanities at American Public University.
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