I’m always surprised at how few home vegetable gardeners make use of cover crops- or green manures- in their garden. Even in an ornamental garden cover crops can reap humongous benefits.

  For those of you who many be unfamiliar with the concept (shame on you, don’t you feel ashamed, huh?), cover crops are plants grown for the sole purpose of digging them back into the soil. At first thought this seems counter-productive,  Why do it you may ask? Well, The concept goes something like this:

   Deep down in your soil are nutrients that are not readily available or many shallow rooted plants can’t reach . Cover Crops such as Daikon Radishes and Rye are excellent at sending down very deep roots and drawing these nutrients up into the plant. Right before the plants flower you mow them down, let them dry into hay, and then dig them into the soil. Once the plants decompose, this makes those deeply stored nutrients available in the top few inches of the soil where they can do the most good. Cover crops of this kind do not add anything new to the soil. They just make what’s already there more available for future plants. 

  Another class of cover crops, the legumes, are grown for their super-duper nitrogen fixing ability. Plants like peas, clover, and beans have little colonies of bacteria living on the roots of the plant that take nitrogen from the air and supply it directly to the legume plant.  By growing legumes as a cover crop, however, you add significant quanities of nitrogen fertilizer once the nitrogen rich plant topsand root systems are dug into the ground to decompose.

The benefits of cover crops are more than just recycling and adding nutrients. They can be used to suppress weeds, control erosion, discourage pests, and greatly increase soil organic matter. Soon I’d like to write a much longer post on cover crops in general, but in the meantime I’d like to focus on one particular champion plant- Cowpeas.

Whatever you call them- cowpeas, southern peas, black-eyed peas, crowder pea or whatever- They’re a warm weather summer annual that makes the best pot of dry beans in the world. However, you’re not going to let them get that far. As with all cover crops, you want to cut it down just before it flowers. If it bothers you to have a spot in the veggie garden that you aren’t harvesting from in the summer months, the leaves are used as a potherb in Africa. You could give them a try but don’t blame me if they taste terrible.

  You want a bush variety for a neat appearance. Cowpeas germinate very easily, like most beans. What I do is chop of the soil lightly with a spade, fork, or a small tiller, broadcast the seed evenly, and then rake dirt back on top of it. Before long the seedlings will start poking up, and if you blink, they’ll be about waist high.

  So what’s so great about this magical bean? If you are a connoisseur of cover crops, you may have noticed the fact that the majority of recommended species seem to be cool and cold weather crops. Colder weather, when less vegetables can be grown, is usually the best time to grow a cover crop due to less demand for space in the garden. Growing a cover crop in the summer would take away a precious chunk of your growing season. However, when you unleash the power of the cowpeas, you can do both a summer and winter cover crop with this fast growing, nitrogen fixing cover crop.

Let’s analyse, shall we?

Early April- Let’s say you live around Denver, Colorado in USDA zone 6 (maybe you really do!). You have a bunch of beautiful romaine lettuce seedlings you started inside. The calendar says to plant lettuce out 45 days before frost, so that’s what you do.

Early-Mid May-They grow beautifully and before you know it the heads are starting to form. Not quite time to harvest the heads yet. The last frost has come and gone, however. What you do at this point, is get your super duper cowpeas seed and interseed it with the lettuce. Chop up the ground with a hoe around the lettuce, being veeeery careful not to damage the roots of the plants. Then, spread your cowpea seed evenly around the bed/row/whatever. By the time they’re six inches high the head lettuce should be ready to come out.

Mid July- Two short months later and it’s time to cut and dig in the cowpeas. You’re going to let the cowpeas decay in the soil for two weeks, unless you’re pressed for time. If so, ignore the admonition to wait. While this may render nitrogen less avaible for the next crop for a few weeks- despite the impression you may get from garden magazines and county agents- this will not cause the world to explode. It probably won’t make much of a difference to the next planting’s growth, if any.
   Anyway, whether you wait two weeks or not , you soon throw in some cabbage seeds for the fall.

60 days later it’s October if you wait or Mid-September if you don’t. The cabbage is ready to be harvested. This still gives you time to plant a fall cover crop (especially if you didn’t wait) of rye that will protect your soil from erosion all winter, suppress weeds, and add a good amount of organic matter to your soil for next year.

Four crops in one year on the same bit of ground! And that’s in zone 6! If you live in zone 7, 8, or 9, you can grow longer season vegetables in between.

 Last year (in Zone 8b) I grew Sweet Corn-> Cowpeas-> Broccoli->Oats. The combinations are endless, but It takes a little planning to make sure you’ll have time to get that last cover crop in, as you want the winter cover crop to have a few weeks of growth before the really cold rolls around. In colder regions you can substitute one of the vegetable crops with radishes or similarly short season vegetables.  

 Give it a try. You’ll be seriously amazed at how much improvement you’ll soil will get from two cover crops a year!