Cover crops are the last detail, the finishing touch to the end of an autumn season. Nothing will protect a vegetable garden as well throughout a frosty winter with strong winds. Turning over a cover crop in the spring adds humus and nitrogen. It’s the easiest way to enrich your garden and the best insurance that healthy soil awaits when you plant seeds. Most garden centers provide a variety of cover crop seeds, which you can buy by the pound.
I’ve tried most of the cover crops that are recommended: peas, clover, alfalfa, vetches and annual rye. The legume crops, like peas, clover, alfalfa and vetches, do have special benefits. They are nitrogen fixing and will add nitrogen to your soil through their roots instead of depleting nutrients. Annual rye isn’t so remarkable as the legumes. But when incorporated into the soil, rye adds nitrogen from its decomposing leaves.
In zone 5, annual rye is the only cover crop I sow. Others take too long to germinate and grow. By the time winter has arrived, there are patches of bald spots, which never will be covered before spring. Friends who are fortunate to own greenhouses prefer the clovers and often allow them to become perennial covers. They did into the clover and plant tomatoes, peppers or cucumbers.
Since I plan a fall garden of lettuces, arugula and spinach, Colorado offers only a brief window of opportunity to sow and grow a healthy cover crop. Annual rye is perfect and, in a matter of weeks, the garden looks like a shag rug with an emerald green hue.
Often, annual rye is tilled right after it sprouts in the autumn because it quickly forms turf. If you have only a hoe and shovel, it’s easier to till at this stage rather than turn over a thick root system by spring. The drawback to this approach is that you may not benefit from a cover crop that can prevent wind erosion. If you have access to a tiller, it pays to wait. The thick root system will prevent erosion from our gusty winds. Tilling only once, turning over the rye and allowing it to decompose in the spring, adds quick compost. Or, you can end your garden sooner than I do and plant the slower legume crop.
Cover crops take on a greater urgency these days because fewer gardeners are relying on cow manure to condition the soil and provide nitrogen. Dairy and meat producing farms pen cows closely together. Since they are fed diets high in salt to increase milk and meat, their urine is intensely salted. That falls on the manure and adds salt—a potent herbicide. Unless you can buy manure from farms that don’t comply with this practice, you may be salting your garden. One option is to add manure from an animal that can move freely, like a horse or llama.
Also, the E-coli outbreaks a few years ago have made gardeners wary about using any animal manure in gardens where they grow lettuces or fruits that are uncooked. Composting manure presumably kills the E-coli bacteria, but I’ve found wide disagreement about this among experts. Changing weather patterns and the capacity of bacteria to mutate make some scientists cautious.
I’ve given up on animal manure. Instead, I compost every bit of vegetable and fruit leftovers like watermelon rinds, coffee grounds and eggshells. These are thrown into large wire mesh bins with chopped up flower stalks, raked leaves and plant clippings. All turn into a fluffy mixture that goes into the garden. Grass clippings and vegetable peelings provide nitrogen as will your cover crop. You may not notice the difference this combination of vegetarian compost and cover crops makes in the first year of your garden. But year after year, the sheer abundance and health of your plants will reveal the benefits.
Sowing a cover crop begins with removing all the plant debris from the garden. Unlike the perennial beds, where you want to leave seed pods for the birds as winter food, spent leaves and stalks, like tomato vines, simply harbor disease. Seasoned gardeners learn to discard the leftovers from any vegetable plant that was infected with disease or insects.
This is the time to add that layer of compost you’ve been saving. Pile on those decomposed kitchen scraps, the onion peels and carrot shavings that no longer are recognizable, mixing them into the soil.
Rake the soil and broadcast the seed. Water to moisten but not drench. Keep the soil evenly moist until you see seedlings emerge. Within a few weeks you should have a rye crop dense and thick as green fur. You no longer need water the cover crop. Let the winds arrive. Your garden is blanketed until spring.