Choosing and Using Cover Crops

Cover crops are a confusing topic for most gardeners, and no wonder. Most books expect you to plow them under. To gardeners, that doesn't sound doable. But new research shows that soil-building comes easier than that: from roots.

Of course, the top growth is important; preventing weeds alone is a huge benefit. And preventing soil loss.  But out of sight, the roots do much more. Like opening passages for oxygen, feeding earthworms--and dying.

When the tops are cut, the roots die and turn to compost right there in the soil. Compost that you don't have to haul, turn, or shovel. And we aren't talking small amounts here. Winter Rye makes 380 miles of roots per plant. The most fertile soils in the world are grasslands, where the roots grow and die in the soil year after year.

What to Plant? Let Nature be your guide.
Meadows and prairies have a mixture of grasses, legumes, flowers, and taprooted plants. The famously fertile topsoils of the Midwest were built by such plant communities. Use that soil-building synergy in your garden. Your mix should include:

•  A grass (grains are grasses) like wheat, rye, or barley.
• A legume, like vetch or clover.
• A tap-rooted plant like California poppy, chard, or mustard, to improve water absorption, bring deep-buried minerals to the surface, and open the way for crop roots to follow.
• Some flowers keep beneficial insects around--alyssum, calendula, arugula, poppies, cilantro, and chervil work well.
• Agricultural mustard to inhibit fungal diseases like fusarium, and add sulfur, an important nutrient for healthy plant growth.

 
Timing is important
The size of the root system depends on when you plant.  It's best to sow cover crops 2-4 weeks before your  first fall frost. *  Don't be surprised if the plants don't get tall--they will be busy underground. In tests, crimson clover that was was only 2 inches tall by November nevertheless had roots 12 inches deep, with many nitrogen nodules already fertilizing the soil. Rye only 6 inches tall had roots 20 inches deep. All winter, the roots will be holding your soil, providing channels for water absorption, and adding tons of organic matter to your garden.

But how can you plant cover crops when the beds are still full of summer plants? Here are some options:

• Broadcast the seed of your cover crop while the existing crop is still in place. This is easiest if the crop is fairly upright, but possible for most. It's called undersowing. Clover is a great crop for undersowing; it doesn't need as much sun as grains do, and the small seeds don't need to be deeply buried.
• Are your summer crops still actually producing? If they aren't giving good harvests, move on. You'll make spring planting easy by building the soil and preventing weeds now.
• Sow winter rye and clover into any empty space, even if it is not directly in the bed. They will take light foot traffic, and hold the soil during mud season. Great compost material, too.
• If you have to leave a few beds until late, sow rye and mulch it lightly.

Don't forget pots and containers.
A low-growing, cover crop prevents your expensive soil mix from getting washed away or taken over by weeds. Calendula, poppies, salad greens, clover, and peas are great for this. If you aren't using the pot, cover it with its saucer to keep weeds out.

*You can find first and last frost dates online. Here is one place:
https://www.almanac.com/gardening/frostdates