It’s easy to feel powerless in the face of climate change, but as a gardener, maybe you’re not so powerless after all. Two common activities of autumn, composting and planting winter cover crops, result in the sequestering, of isolating, of carbon in the soil. When organic matter gets dug into garden soil, it does not release gases that contribute to global warming and instead creates carbon storage. But that’s just the beginning of the interconnectedness of cover crops, compost and climate change.
Composting to Counter Climate Change
Every bit of food waste, paper, or cardboard you can compost skips the environmental costs of collection (trucks) and disposal (bulldozers), but more importantly diverts those items from the methane gas stream. Methane is a greenhouse gas 26 times more potent than carbon dioxide, and rotting organic matter in landfills emits huge amounts of methane into the atmosphere. When organic matter is composted properly, which involves access to air, very little methane is produced because of the presence of oxygen.
Late summer is a great time to get composting projects up and running, because most of us have plenty of weeds, spent plants, and sticks to add to the heap. Warm temperatures support the work of the microbes that break down organic matter, so compostable materials gathered now stand a good chance of rotting by spring.
If it makes you feel better about climate change, and to amuse your green-minded friends, you can refer to making compost and adding it to garden beds as carbon fixation. Ditto for turning under green manures or old mulches, or mixing grass clippings into your soil. All types of vegetative organic matter, dug into the soil, are deposits in your garden’s carbon bank.
Store Carbon Using Winter Cover Crops
Whether with a garden spade or a plow, the soil’s cultivation zone goes only about 12 inches (30cm) deep. You can add carbon from the top via compost, mulch, or green manures, but what if you want to take soil’s carbon storage potential deeper, into the subsoil?
In the last 20 years, agricultural researchers in China, Europe, and the USA started studying ways to increase soil’s carbon storage capacity while using it to grow crops. After looking at dozens of cultivation practices, they learned that composting and green manuring (turning under lush green vegetation and allowing it to rot) cranks carbon storage in the topsoil, But when it comes to increasing the soil’s carbon-holding capacity by going deep, winter cover crops are the champs.
This is an old, old idea. Winter cover crops including winter rye, wheat, crimson clover or phacelia send down roots more than 48 inches (100cm) deep, and when those roots rot, they become storage channels for water and carbon. It doesn’t matter how you handle the cover crop’s top growth – most gardeners cut or pull it and use it for compost or mulch – the deep root channels persist as threads of cached carbon.
Winter cover crops also benefit vegetables grown the following season, sometimes in a huge way. In my climate, both crimson clover and hairy vetch survive winter when protected from deer. Both plants fix nitrogen, plus they do things to the soil (and subsoil) that makes my tomatoes extraordinarily happy. In September, when I sow the winter cover crop in next year’s tomato row, I’m staging a triple win for my tomatoes, my soil, and the planet.
Amidst the fires and floods, it feels good to be doing something. This fall I’m building two compost piles instead of one, planting cover crops in every vacant bed, and keeping the green season going as long as possible. Every little bit helps.