Most organic growers in California grow cover crops to protect their soil and build fertility naturally.  They are not harvested for a crop, but rather fed back to the soil.
The primary season for growing cover crops in our area is winter, when the harvest season for most crops is over and rain provides natural irrigation.  But at Terra Firma, we plant just as much acreage of winter crops as summer.
Our winter-harvested fields take a beating many years.  We’re out there in the rain, wind and mud walking and driving on them.  The soil gets compacted and crusty. Many of our winter crops are harvested too late in the spring to get re-planted with a summer crop.  And if we do put a summer crop in after a winter one, the results are never optimal.  The fields are tired and need a break.
For ten years, we experimented with different cover crops we could grow in the summer.  We needed something that didn’t require a lot of irrigation, grew fast, and competed well with aggressive summer weeds.  At the time, literally no one in the Sacramento Valley grew summer cover crops.
Legumes like beans were particularly appealing because they fix nitrogen from the atmosphere, providing fertilizer for the crop that follows them.  And they like hot weather.  But most of the beans we tried simply required too much water, grew too slowly, and didn’t compete well with weeds.
We found that Black-eyed peas liked hot weather and grow more vigorously than other beans. We discovered that there are several varieties of “cowpeas”, as they Black-eyed peas are known in farming circles, that are not grown for human consumption but rather for grazing and livestock feed.  Farmers in the South grow them during the summer when it’s too hot and humid to grow many cash crops.
Turns out that these cowpeas grow exceedingly well here, and are just as tolerant of drought as they are of humidity.  Even in mid-summer here, we irrigate them only twice — at the most.  Planted into moist soil, they will go four weeks before needing any water.  By that time they are often knee high, shading out any weeds that may have sprouted after them.
The cowpeas — called “Iron and Clay” — reach full size in 6 weeks, completely covering the soil with their lush, dark green vines. By eight weeks they start to flower, which means it’s time to graze them with the sheep or mow them, before they start making seeds.  It is truly amazing to see how fast they grow.
This short growth period allows us to prepare the fields in time for our fall and winter crops, which we plant from August through October.  The difference in the soil before and after the cover crop is dramatic, from cloddy and compacted to loamy and loose.
The dry weather we had this spring allowed us to plant more summer cover crop than usual.  To date we’ve planted twenty acres that will soon go into strawberries, garlic, lettuce, onions, and spinach. And there are still a few fields scheduled to be seeded with cowpeas in the next week that will host our first tomatoes, in early spring of 2021.
Summer cover crops are now a critical component in our farm’s plan for economic and ecological sustainability.  They are also easy and fun to grow — a winner all the way around.