Gardener’s gold: what is compost anyway?

Growing up, mom and dad would add compost to our backyard garden soil each season. The recipe for an abundant harvest involved peat moss, manure, and compost – whatever that was. Somehow we intuitively understood that this was the magic ingredient that made the cherry tomatoes sweeter, the rhubarb stalks brighter, and the spinach crisper.

It’s true – compost does for plants what nothing else can. It literally feeds the soil a smorgasbord of micro and macro nutrients far beyond the basic nitrogen, phosphorus, potassium trinity-in-a-bag blend. It improves moisture content and overall density when added to soils and clays, which is why great garden soil feels so fluffy that you can just imagine a plant’s excitement to send out roots like a child squishing her fingers into beach sand.

What researchers have learned is that, if plain old soil is just a mass of nutrients for plants, compost adds to that a vastly diverse ecosystem of bacteria and fungi to help transport those nutrients and moisture in the soil so that plants grow more readily and are more resistant to environmental extremes. In one study, compost helped double crop yield per acre and has enabled food production in desert soils and clays. But compost is not literally magic as I had once thought. So what is it?

Compost is an organic material comprised primarily of organic waste that has been decomposed by microorganisms. You can think of organic waste as anything that was recently alive such as leftover food, yard waste, mulched tree trimmings, etc. though there are other examples like minimally processed paper products.

To make compost, you can’t just dump grass and/or food in a pile and watch it transform into compost. The bacteria that turn waste into compost need some of the same things humans do – food, water, air, and a comfy place to live. This is why backyard piles of grass clippings often don’t turn into compost. The grass compacts tightly, blocking air from getting in, and often we don’t think to add moisture to the pile periodically.

First, you need a significant size of compost heap such that its core will remain warm and moist. We recommend approximately 3-feet cubed for a pile that will be in the open (container composting can be done with smaller amounts of material). Next, mix wood mulch or other organic matter that won’t easily compress, called a “bulking agent”, that will create and protect pockets of air throughout the pile. And finally, keep the heap moist by loosely covering it with a tarp and/or occasionally spraying it with water. A simple test is to squeeze a handful of composting material. If it stays clumped together without moisture squishing out, then it’s moist enough. If you’ve over-watered it, turn the pile with a shovel and keep it uncovered until it dries some. Over-wet compost starves oxygen-loving (aerobic) bacteria, which allows other (anaerobic) bacteria to start digesting instead and producing methane. This is why compost piles have a reputation for smelling bad.

What if I want to compost food scraps? When will I know my compost is done? How much is this helping the environment?

October is KC Compost Awareness month. Throughout the month we will be sharing information about how to compost as well as the impact composting can have on air quality, food insecurity, and sustainability. Whether you want to compost in your back yard or join Food Cycle KC to collect and compost your food waste, getting started is the most important part. As Shia LaBeouf reminded the Internet comically (we think?), “just do it.”