Tomato Patch: Time for Green Manure?

Green manure--or something else?

I’ve bought many bags of composted manure over the years, and when I opened them in our garden, the manure was dark brown.  When I buy a pickup load of composted horse manure and shredded leaves at the Howard County Recycling Center, the compost is, well, dark brown.

So what’s with “green manure”?

“Green manure” is the name often given to plants that overwinter on tilled fields and then are turned under the next spring.  Another term is “cover crop.”  Whichever term you prefer, it has two basic purposes, to enrich the soil and protect it from erosion by winter weather.

The University of Maryland Master Gardener Handbook explains “cover crops” this way in its “Vegetables” chapter:  “Cover crops are mostly small-grain species, like oats, rye, and wheat, and legumes, like clover and vetch. …  These crops are typically planted as early as August 1, but no later than October 10.  They should make some growth before the first hard frost.  Some are killed by cold winter temperature, but most go dormant and resume growth in the spring.  Cover crop roots grow deeply into the soil pulling up nutrients that might otherwise leach out of the soil.  The crops are turned into the soil before going to seed, usually sometime from mid-April to early May.”

A Handbook table lists these typical cover crops with directions about when to plant seed and when to turn the plants under in the spring:  alfalfa, barley, buckwheat, crimson clover, forage radish, spring oats, winter rye, hairy vetch, and winter wheat.

I began thinking about “cover crop” when I tore out the dying vines of Tomato Patch 2011.  Should I plant a cover crop?  Are there alternatives—especially for small, hillside plots that this gardener tills—a youth-challenged gardener, by the way, who is prone to “aching back”?

Thinking I might experiment with a cover crop, I hopped into my Tacoma and drove up to the Southern States farm supply store in Ellicott City, the one place in Howard County that I thought would stock cover-crop seed.

“Do you have seed for any cover crop?”

“Sorry, not today, but next week we’ll be getting in a mixture of rye and wheat.”

“Will it be in bulk?  I only need a few ounces for my garden.”

“The smallest size will be three pounds.”

Straw mulch will work

So much for my Green Manure Experiment.  Back home, I looked at the vineless Tomato Patch and decided on an alternative to a cover crop.  I had mulched our tomato plants in the spring with straw which now was starting to disintegrate and become part of the garden soil, but it is still recognizable as straw.  If I don’t turn it under to hasten decomposition until late winter, it can serve as a “cover crop” to protect garden soil from the ravages of winter storms.

So this winter Tomato Patch is sporting a straw “cover crop” that died in 2010 or earlier and in color is definitely beige, not green.  Will this crop improve the soil?  Little, if any, I suppose, but I think it will do a reasonable job of protecting the soil from the elements.

And as I rearranged the straw to cover as much of the soil as possible, I thought of a very positive outcome of my choice:  the straw will continue to decompose over winter and I’ll have a relatively easy time “turning it under” with my garden shovel in late winter.  Manually turning under a cover crop can be an “ache in the back,” to say nothing of muscle pain.  Score one for the Ancient Gardener.

What else could I have used?

Grass clippings or shredded leaves will do too

Since I don’t have enough straw to spread on all my small hillside garden plots, I protect the soil—and enrich it to some degree—with whatever I have at hand.  I’ve already spread grass clippings on two or three plots—sort of a wimpy “green manure” approach, wouldn’t you say?  When leaves begin to fall, I’ll bag some with our lawn mower and spread the semi-shredded leaves like a brown blanket on other plots, where they’ll also both protect and decompose over winter.

Disappointed that I couldn’t buy a small amount of cover-crop seed locally, I checked availability on the Internet.  Territorial Seed Company has a paragraph explaining cover crops with several links you may enjoy investigating, including one showing varieties of available fall-sown seed.  Johnny’s Selected Seeds also lists a variety of seeds under “green manures.” 

There is one green-manure cover crop I don’t want to grow—winter weeds.  Alas, winter weeds are sprouting everywhere these days and growing rapidly in this extra-warm October.  Today’s chickweed seedlings might protect the soil over winter, but by early spring they will have become thick mats and will have sown thousands of seeds for future crops.

To read the University of Maryland Extension's one-page fact sheet on cover crops, CLICK HERE.
If you’re a new reader, check out my earlier postings about Barbara Billek, who uses hairy vetch as a cover crop in her raised vegetable beds, and Susan Levy-Goerlich, who uses shredded leaves to protect her garlic crop over winter.