By Julie Riley
Once upon a time in a summer without COVID-19, I thought it would be great fun to make composting a public event. Staged in a city park, it would feature contestants noted for their composting prowess, who would have two weeks to make compost. Compost feedstocks would be dumped, the whistle would blow and those who had taken up the challenge would begin. Contestants would camp out next to their piles to prevent tampering. Family and friends would stop by to cheer on their favorite composter.
Local celebrity judges, knowledgeable of what good compost should be, would poke, prod and sniff before declaring which compost was best. The winner would divulge the techniques they had used as onlookers sifted handfuls of dark, fluffy compost through their fingers.
Compost happens. You’ve seen the T-shirt. Pile up organic debris and eventually it will decompose, but this laissez- faire approach will not win you any contests. If your goal is to produce compost quickly, you’ll need to create an environment hospitable for the microorganisms that will turn your organic waste into black gold. Provide the microbes with necessary food, water and air and their populations will skyrocket.
As they digest the materials being composted, the carbon in these feedstocks is used as an energy source and the nitrogen to build proteins. Feedstocks each contain a certain amount of carbon and a lesser amount of nitrogen, which can be expressed as a ratio. The C:N ratio of sawdust is about 200:1. This means sawdust is high on the carbon side of things. For every 200 parts carbon, there is one part of nitrogen.
If you’re not in a big hurry for finished compost, there’s no need to bother with C:N ratios. When building your pile, alternate layers of fresh, green materials with dry, brown materials and call it good enough. To produce compost more quickly, you’ll need to be more scientific. Select feedstocks to give your pile a C:N ratio somewhere between 25:1 and 30:1. The microorganism population will flourish and your pile will heat up quickly. You can find lists that give feedstock C:N ratios, but a compost calculator comes in handy if you’re composting more than one material. The calculator provided by Klickitat County, Washington, is easy to use. Select the materials you plan to compost and adjust quantities until you reach the C:N ratio sweet spot. The calculator is available at bit.ly/3742kOD.
Before a compost pile will heat up, it requires a certain mass. Collect enough materials to create a pile that will be at least 3 feet by 3 feet by 3 feet. Build the pile by adding feedstocks in alternating layers, taking care to wet dry materials as you go along. It needs to be wet but not too wet. The microorganisms you are counting on need air to survive. A soggy pile will turn anaerobic and smell foul.
Aeration is one reason you turn a compost pile. Another is to be able to move uncomposted material from the outside of the pile to the center where the microbial population is most active and producing heat.
“Temperature is key in determining when a compost pile should be turned,” says Jodie Anderson, director of the UAF Matanuska Experiment Farm and Extension Center in Palmer.
“It’s time to turn when you notice a decrease in temperature,” she said. “You don’t need expensive monitors that send readings to your phone. Stick your hand in your pile once a day and you’ll know when it’s cooling down.”
I’ve had an opportunity to work with some great people over the years. A cohort on the Kenai Peninsula wore out a chipper/shredder in one summer. He hauled it around to demonstrate to Master Gardeners how much faster they could make compost by chipping or shredding their coarse materials. The principle is the same as when explosives are used to dispose of large animal carcasses. The smaller the particle size, the faster the decomposition.
To try to make compost in two weeks, you have to really work at it. Build your pile all at once. Don’t keep adding to it. Determine the amounts of each feedstock to use based on C:N ratio. Chip or shred pieces of wood and vegetable stalks that are slow to break down. Pay attention to moisture. Turn the pile often, as soon as the temperature starts to drop. Finished compost will look and smell like soil. At this stage, you can let it sit longer to cure.
For more details, check out UAF Cooperative Extension Service’s composting publications by typing UAF CES publications into your computer’s search engine.
Julie Riley is a horticulture agent with UAF Cooperative Extension Service in Fairbanks. If you have composting issues you’d like to discuss, please call or text her at 907-230-7339. Extension’s Tanana District office is currently closed because of COVID-19.
