When the folks at Kirtland Elementary School decided to start a garden, they were faced with barren soil and the costly and labor-intensive prospect of hauling in many loads of compost or topsoil.
“It was just straight up sand, no nutrients,” said Kendal Chavez, a FoodCorps service member working with the school on the garden and teaching the students about healthy food.
She devised a twofold strategy of adding compost to the garden plots but also using cover crops to amend the soil and get it ready for planting.
“We were looking for something that would be more sustainable,” Chavez said. “Cover crops are a fairly cheap, easy way to enrich the soil.”
Cover crops, also known as green manure, can be used anywhere from small backyard vegetable gardens to agricultural fields. The basic idea is simple: Grow plants such as buckwheat, winter rye or peas that can add nutrients to the soil and then till them under and let them decompose.
“Anybody can do it, but organic growers have to worry an extra amount about keeping organic matter and nutrients in their soil,” said Cheryl Kent, a Bernalillo County Extension horticulture agent.
In addition to adding nitrogen and other nutrients, cover crops help stabilize the soil and prevent erosion. They also can choke out weeds and provide habitat for insects, animals and other organisms.
A side benefit for avid gardeners who get antsy during the winter months when there’s not much for them to do except clean tools and peruse seed catalogs is that they have an activity in the garden, said Rick Hobson, owner of Jericho Nursery.
And now is the time to plant a winter cover crop. Winter is the time most gardeners choose for a cover crop because they avoid taking a bed out of production during the spring or summer growing season.
“August is perfect through mid-September … after that it starts to get a little late,” Kent said.
There are two basic types of cover crops: grasses or grains, which add organic matter to the soil, and legumes, which also add nitrogen.
If you think your soil is nitrogen-deficient or you plan to grow something in the next season like leafy greens that need a lot of nitrogen, you might want to choose a legume, Kent said.
Good cover crop choices for the Albuquerque area are wheat, oats and winter rye. Good legume choices are hairy vetch and Austrian winter pea, Kent said.
Other nitrogen-rich options include buckwheat, pinto beans, clover and vetch. Another grain choice is millet.
Clover is very easy to grow but it needs more water than other crops and can be invasive, Hobson warned.
“I’ve had it completely take over lawns,” he said.
Cover crops are started from seed, and seeds are available at nurseries or by mail. Plant them as you would any other seed crop. They should sprout and grow in the warm weather and then go somewhat dormant over the winter. Water as needed to keep them alive. Once the weather warms back up, the plants will start growing again.
When planting legumes, make sure the seeds already have been inoculated or buy inoculant and do it yourself. Inoculants help to fix nitrogen on the roots of legumes; you can see it as small bumps.
As spring approaches, watch the plants so you can catch them just as they start to flower or just before. That’s when the plants have not yet gone to seed and have the most nutrients stored.
“That’s the time to cut them, mow them, destroy them, till them in and include them into the soil,” Kent said. “That’s what gives you the maximum benefit.”
Oats are a little different. They will die back when they freeze and can be left standing until spring and then tilled in.
Peas planted in a protected area in the fall can be fun. “You get both. You get the harvest and you get the green you can till back in,” Hobson said.
Tilling can be done with a rototiller or a shovel or fork. If there’s too much organic matter, it’s fine to cut some off and compost it. It’s also OK to chop up the cover crop material and let it break down on top of the soil and then plant directly into it.
The last step is to wait about two weeks for the material to break down before planting a regular crop. To help grass or grain crops break down, gardeners can add nitrogen such as manure or blood meal, Hobson said.
At Kirtland Elementary, Chavez and the students planted a cover crop of winter rye last year. After they tilled it in this spring, they noticed a difference in the soil.
“It’s darker already, definitely changed in color and it holds together a little better,” Chavez said.
The rye didn’t add nitrogen, so Kirtland now has a summer cover crop of pinto beans, mung beans and buckwheat growing together. Mixing crops adds diversity to the ecosystem.
“Everything’s healthier when you have different plants,” Chavez said.
Cover crops can be grown in spring and summer as well as winter. Sorghum and Sudan can be planted in late March or April. Oats should be planted after the danger of frost has passed, Kent said.
For a quick turnaround, cow peas can be planted in late February and tilled under in time for a regular crop to be planted in June, she said.
Cover crops are versatile and can be planted at various times of year and alone or in combinations.
“People shouldn’t be afraid to experiment a little bit,” Kent said.