You did a good job last fall getting cover crops planted. Now, they’ve taken over your garden and you don’t quite remember what you had planned to do with them. What you’ve done is to grow great biomass for your garden that you can use as compost material or cut down as mulch right where it was grown. Give yourself a pat on the back! The next step is to cut it down at the right time as mulch-in-place or cut it and put the material in the compost pile. At this stage it is all green matter and your compost would benefit from an addition of an equal amount, by volume, of dry, carbon material. At this time of year my carbon comes from Jerusalem artichoke stalks, or sorghum and cornstalks that I put aside in the fall. Maybe you have access to leaves, hay, or straw. If you are bringing in that material from outside sources, read my post Killer Compost to know what to look out for. Water well when building your compost pile.
Last May I wrote Cutting a Rye Cover Crop at Pollen Shed. It speaks to the importance of cutting your cover crop, in that case cereal rye, at the time when it has reached its most biomass, just before it produces viable seed. For any crop, that would be when it is flowering. You don’t normally think of grain crops with flowers, however, you will see where the seed heads begin to form and the pollen will be hanging off it. If you cut it earlier than that, the rye and wheat plants, like the grasses they are, will grow back. If you wait too long, seed will form. That’s okay if it’s seed you’re after. In that case, you would wait longer to cut it and need to make sure the seed has matured. One way to test is to cut a few seed heads and thresh out the seeds in your hand. If you don’t get seed that looks like what you planted, it’s not ready. After the plant has put its energy into seed production, it begins to die. You will see the rye and wheat plants begin to turn brown when it is time to harvest the seed. The harvest will be seed and straw and usually occurs here in mid-June.
Here in the Mid-Atlantic in zone 7 our last frost date is around April 26. Cereal rye is my major cover crop and generally sheds pollen around the end of the first week of May. That’s also about the time that the farmers who are on top of things are making their first cutting of hay. This year, however, the weather seems to be all mixed up. We didn’t have much of a winter and warm weather arrived early. Usually we have a spike in the temperature in the second week of April, fooling people into setting out their tomatoes, only to turn colder before the weather has settled. The weather did a good job convincing my rye that warm weather was here and it flowered early. I cut it in the beds where it would be left for mulch on April 20. I’m really interested to see how the rye and wheat do that are in the beds to be grown out for seed. The temperatures here dipped into the 30’s on April 24th and 25th after nighttime lows in the 60’s on April 16th and 17th. Looking back to my temperature records from last year, I see that the April nights were consistently warmer in 2011. Last year I cut the rye for mulch on May 10. It must be the lack of winter this year, not warm April nights that brought the rye to flower earlier in 2012. My video Cover Crops and Compost Crops IN Your Garden shows my management of this system.
It might be that you have grown Austrian winter peas or crimson clover as your cover crop. These crops are legumes which fix nitrogen from the air in the nodules on their roots, returning that nitrogen to the next crop as those roots decompose in the soil. You could cut these crops at flowering and let them lie as mulch, as with the rye, but their biomass wouldn’t be as long lasting as the rye. They are best used as green material for the compost, adding carbon to capture all the nutrients as composting occurs. Crimson clover, not to be confused with red clover, is a beautiful plant that generally flowers here around mid-April. The legumes can be easily pulled out or cut for compost material and the bed planted soon after. I wait two weeks to transplant after cutting the cereal rye beds for mulch, but I could transplant sooner than that into the legume-only beds. If I was seeding into the beds, I could easily do that in a legume bed two weeks after cutting. If I was only after the biomass and in a hurry to get the next crop in, I would cut crimson clover as soon as it has flowered. However, I have bees that enjoy it, so I wait a little longer before cutting so they can have the most benefit from the clover blooms.
Sometimes hairy vetch is planted in the fall to precede tomatoes. I’ve done that in two tomato beds this year. I prepared the beds last fall and moved the tomato trellises there at the same time. The vetch grew up and I cut it April 25. My tomatoes are ready now in the coldframe for planting out. I started the seeds there on March 16. Having grown in the coldframe, they are already acclimated to the outdoor temperature fluctuations. Sometimes hairy vetch can be a nuisance in the garden. In the past I’ve used it as a companion to the wheat and rye and you can see that in my cover crop video. You can also see how it became a problem in the rye.
It is good to plant a small amount of a legume into your grain crops and the legume I use now is Austrian winter peas, a winter hardy variety of field peas. Both the vetch and winter peas will grow quite tall and could pull down the grain if left to grow. That doesn’t matter if I’m just cutting the crop to lie down as mulch, but if I want the grain later in the season I need to pull out the vetch or winter peas. Austrian winter peas are much easier to pull out than the vetch. If you are growing grain on a larger scale than your garden bed, you might choose red clover as the companion to the wheat or rye. You can seed it into the growing grain in the spring. The red clover will grow some and provide a nice green cover when the grain is harvested, then it will keep on growing and a harvest can be taken the first summer. Let it grow over the winter, then harvest twice the second summer. After that it is time for another crop for that space.
You can find the best cover crops for your location and situation by reading Managing Cover Crops Profitably, 3rd edition, available from www.sare.org. Be sure to read all the text, not just look at the charts. There is a lot to learn and every time you think you have it down, something else comes along to figure out. The important thing is to let the soil and the garden guide you.