Cover Crops and Garlic: Blog 24 in a Gardening Series

A version of this column first ran in the Roane County (WV) Reporter and Times Record. Support local journalism! Subscribe to your local newspaper. This is one of a series of blogs for new gardeners. Start reading the whole series here: Part 1. 

Cover crops, also called green manure crops, are those planted for their effect on the soil and enhancement of subsequent crops rather than for direct use. There are a variety of types and species, and this is a complex subject which I’m still learning about. Now is the time to sow many cover crops, so I will devote one column to the subject.

Cover crops can be used in summer or over the winter. For some the purpose is simply to keep the ground covered—bare soil leads to erosion and temperature extremes, and is harmful to the myriad organisms that create healthy, fertile soil. Of course, keeping the soil covered over winter (or a fallow stretch during the growing season between crops) could be accomplished just by throwing down hay or some other mulch.

I do this with some beds, particularly where I have fully prepared the bed in fall for the crop I plan to plant early in spring. Most cover crops that overwinter require some degree of tilling in; for the earliest crops like peas, onions and greens, which I plant in March, I like to have the ground fully worked in the fall. Usually I turn the bed with a shovel after removing weeds and the residue of the previous crop and any mulch, then I add organic matter (compost, leafmold or manure) and sand if the soil has reverted too much to clay. I work it in with my hands. If I get this done in fall and cover the bed with hay, I can remove the mulch in March and find the bed ready to plant. Since my beds are somewhat raised, they are often dry enough to work long before flat ground is ready in spring.

There is one crop that goes in even earlier: garlic, which is generally planted in October. This year I’ve gotten those beds ready early so I put hay down to keep the soil moist and weed free until I’m ready to plant the garlic. First I will go through my garlic and remove any head with a soft clove, dispose of the rotten ones and use the remaining cloves of those heads first. At the same time I’ll pick out the biggest and best of the garlic and separate the cloves for planting, in rows six inches apart. Keeping it in neat rows makes weeding easier. It will make some growth in late fall, usually disappear in the coldest part of winter, and return in early spring. You can use grocery store garlic, just be sure to select garlic you like.

One category of cover crops is legumes, which fix nitrogen. This is key to healthy growth next year. I don’t use fertilizer, which isn’t necessary as long as I return enough organic matter to the soil to make up for what I’ve removed in crops and weeds. Clay soil is hard to work with but rich in nutrients — mine tests high in the primary nutrients so my soil improvement efforts are focused on the texture of the soil more than the chemistry. I have an additional reason for using legumes: two of them, hairy vetch and winter peas, are very hardy and easy to remove in spring. Another category is clovers, which I don’t use because they become persistent weeds, but farmers use often.

Vetch is a frilly plant, not killable by our winters, which can go in until November. If you let it grow until May it has pretty purple flowers on flimsy vines, but if you let it go longer it will drop seed and may become a weed. The winter peas are not quite as hardy and may die in a particularly cold winter here, but usually survive. A virtue of the peas is that the growing tips make a nice addition to salad. Maximum nitrogen is delivered if you turn either of these under when they’re flowering.

There are hardy winter grasses whose purpose is to spread roots deep underground and add organic matter to the soil. Rye, wheat and some kinds of oats are in this category. I plant one of these in my patch of flat ground along with vetch most years. You can just broadcast the seeds and rake them in. But they make tough grassy growth that isn’t easy to turn under in spring if you have clay soil. In the flat ground we use a tiller (after mowing if necessary). I sometimes plant a bed or two in the main garden in wheat or rye with vetch or peas, and let it grow until it flowers in June. If you cut it then, it will generally die back and two or three weeks later you can plant a late crop in the aisles where the vetch or peas had been, or rip out the decaying grain stumps. It’s also a choice to let a grain go to maturity and harvest it for table use or to feed animals; but I have had trouble with the harvesting, threshing and winnowing, or had bugs or mold invade the grain.

Another category is winter radishes, daikons, that plunge deep into the soil with roots up to two feet long… and then die in the cold part of winter. The roots rot and leave a spike of organic matter in the subsoil, breaking up compacted soil. The trick is to plant them early enough, usually August in our area. It’s too late for this year.

The final category is tender plants whose purpose is to improve the soil and fend off weeds. Buckwheat does this and delights the bees when it flowers. It only needs a month, and if it does go to seed, the plants are so easy to get rid of that I don’t mind. It’s also too late for this year; I mostly use it in intervals between crops during the growing season. There are hefty grasses like sudan grass that are serious soil builders, but they take months and are hard to turn under if you haven’t got a tractor. Neither of these fix nitrogen, but there is one plant in this category that does—Sunn hemp. These grow seven feet tall and have pretty yellow flowers if you get them in early enough (also too late now). They make rather stout stalks but you can clip them and lay them on the bed to hold the soil over winter, then stomp on them to break them into bits for faster composting in spring.

Farmers Friend sells cover crop seed. I know of no one else in Roane County but get it from Green’s in Charleston if I can’t get it here.

Read the rest: Part 1. Part 2. Part 3. Part 4. Part 5. Part 6. Part 7. Part 8. Part 9. Part 10. Part 11. Part 12. Part 13. Part 14. Part 15. Part 16. Part 17. Part 18. Part 19. Part 20. Part 21. Part 22. Part 23.