Notes from the Field: Cover Crops

As much as we love the edible fruits of our labors, some of the most satisfying crops we grow are ones that we don't harvest. A key part of organic farming, at least in our non-governmentally-approved definition, is the building of soil. In our minds, this means creating a resilient and healthy ecosystem filled with micro-organisms from insects and worms to bacteria and fungi, with a physical structure and chemical balance that supports crops as they take root quickly, grow vigorously, and become a robust plant that tastes delicious and yields well. In the rest of our bodies - well, you can just tell when the soil is good. Digging sweet potatoes last week, we were overjoyed by the dark, crumbly, rich texture, easy to sink a fork into and filled with earthworms. In the broccoli field near the CSA shed, the dark blue color of the plants is an indicator of their vitality. In the very dry days of midsummer, though, the soil seems to lose structure, and plants don't take off the same way; we have significant disease issues in several of our crop families; and there are 'trouble spots' in some of the fields where plants act different, remaining small and spindly despite getting the same treatment as their companions in other rows. We have a ways to go before our soil is exactly the way we want it.

One of the ways that we work to leave our soil better than we found it - a tall order, since it is inherently prime agricultural land -- is by planting cover crops, sometimes also called 'green manures'. These are crops that grow in the fields when we don't have cash crops there, and while all are key soil builders, keeping the soil in place and adding organic matter when they are turned back in, some have specific jobs to do. In the early spring for the past few years, we have planted field peas on land that doesn't need to get planted into vegetables until late May or June. Peas are great nitrogen fixers, capturing nitrogen from the atmosphere and converting it to a form that is useable for crop plants that follow them; this means we can reduce the amount of fertilizer we apply to those crops when they do go into the ground. Peas also disappear quickly when we turn them into warm late-spring soil, so they are great early season green manures.

This year, on the recommendation of the wise farmers at Roxbury Farm, we tried an early season mix of peas, oats, and bell beans -- a kind of small fava bean -- before some of our fall broccoli and cauliflower. The beans and peas are both nitrogen fixers, and the oats, which come up quickly, are a 'nurse crop' grain, adding organic matter and bringing up minerals from the soil. We seeded this cover crop in April, turned it in with the tractor in mid-June, and planted the brassica crops in July. The result, with a little help from some alfalfa meal and kelp meal, is the beautiful blue-green field beyond the CSA shed -- the plants there are big and strong and healthy, despite being planted in the midst of the dry weather back in the middle of the summer. They are maturing quickly, each variety in its own time, the way we like them to, and are not succumbing to any of the many diseases or pests that can sometimes plague their family at this time of year. It's interesting to compare that field with the one behind the plum tomatoes, which also has broccoli and cauliflower in it, but following a cash crop of snap and snow peas rather than the cover crop mix. These were also planted about two weeks later, so they are smaller for a reason; we'll see what the final harvest and disease picture looks like, but the initial results of our highly unscientific experiment in cover crop management are positive.

At this time of year, we start seeding cover crop combinations on all the land where the vegetable crops are finishing up for the season. We generally try to plant pairs of crops, including a legume to fix nitrogen (which is otherwise a very mobile nutrient that is easily lost to the atmosphere or groundwater) and a grain to hold the soil in place over the winter, collect minerals, and add organic matter when they are incorporated. From the beginning of August through the beginning of September, if we have any space that we're not immediately re-planting with fall greens, we like to seed oats and field peas. These two crops grow through the fall and then 'winter kill' in our climate, forming a beautiful golden mat that is very easy to turn in in the spring, perfect for early crops like beets and carrots. After about the second week of September, oats and peas probably don't have enough time to put on good growth in the fall, so we seed a second cover crop pair, rye and hairy vetch. In this pair, vetch is the legume and rye the grain. Vetch, rumored to be a more efficient nitrogen fixer than peas, is also a good weed suppressor and soil conditioner -- but it is slow to establish and needs the 'nursing' of the rye to help bring it along. Both of these crops will survive the winter in Massachusetts and resume growing in the spring -- sometimes too vigorously, if we don't keep an eye on them! We sometimes mow them right when the vetch begins to flower (usually in May) and then turn them in with a moldboard plow or disk harrow before making beds for our crops.

If you walk around the farm at this time of year, you'll see it all: crops right at the peak of their growth, like the broccoli; crops that are finished, like the tomatoes; crops that have already been turned in, like the crops in our around-the-corner field just beyond the treeline. If you look carefully, you can see the delicate spears of the oats and the curly tops of the peas just coming up in the furrows where the disk harrow scratches them in. They are especially beautiful in the early morning when they carry a heavy blanket of dew. To me, the sight of these crops feels deeply right -- it means that we were able to get our crop out, get the weeds turned under (weeds, by the way, should not be underestimated as cover crops in their own right, although sometimes they can host pests or diseases that can have a negative effect on the following crop), and get the cover crop planted -- a 'thank-you' to the soil, and a way to help prepare the fields for the season to come.

Enjoy the harvest!

- Amanda, Andy, Erinn, Dan, Larisa and Lauren