Covering Your Assets

Oats and crimson clover sprouting in a cleared area of the garden.

Whether spring, summer or fall, I find something satisfying about clearing plants from the garden. I love the way the garden takes on a more spacious, tidy look after sprawling and declining plants are gone.

But that doesn't last long. In spring and summer I'm likely to plant another veggie crop there, or I will plant a cover crop. At the very least, I will cover the soil with old hay.

Without a doubt, soil is your biggest asset in the garden, and keeping the soil covered is one step in building and maintaining healthy soil, alongside adding compost or other forms of organic matter, avoiding walking on and compacting the soil, minimizing tillage or other disturbance (including cutting off annual plants with extensive roots systems at soil level instead of pulling them), and maximizing the diversity of crops in the garden (including rotating crops, companion planting, and cover cropping).

Buckwheat seedlings cover the bare spaces between the celery and parsnips. 

Buckwheat makes potassium in the soil available to other plants.

Maintaining living roots in the soil is possibly one of the most key ways to create healthy soil (which is much more than just dirt), according to the Extension horticulture agent who gave a presentation on cover crops at last month's Master Gardeners' meeting. Those roots give beneficial microorganisms (mainly bacteria and fungi) someplace to live.  Without those organisms plants will not thrive, as the microorganisms in the soil assist the plant in taking up nutrients. You can maintain living roots in the soil three ways:

   --By planting perennials; which only works if you don't plan to use the area for annual crops for a while;
   --By intensifying crop rotation. This means that as soon as you take out one crop, plant another, preferably from a different plant family, but not necessarily. I usually plant my fall brassicas (cabbages etc.) in the same places I planted the spring brassicas. Then I give that area a rest from brassicas for the next two years.
   --By planting cover crops, which are the focus of this post.

Besides maintaining living roots in the soil, cover crops also help smother weeds, add organic matter to the soil, prevent erosion and oxidation of the soil (thus, keeping nutrients in place), and in some cases, make nutrients more accessible to other plants.

Examples of the last benefit include legumes "fixing" nitrogen in the soil through a symbiotic relationship with certain bacteria; deep rooted plants pulling nutrients from deeper soil levels, making them available to other plants when their upper portions die; and modifying other nutrients to forms other plants can use. Nutrients might be in the soil in sufficient quantity, but in forms your garden plants cannot use. Some cover crops take care of this.

Key aspects to planting cover crops: choose the one right for the season, warm-season covers for late spring and summer, and cool season covers for late summer through winter. Decide whether you want a high biomass crop (which gives you lots of green growth that breaks down slowly), or a low biomass crop (which is not as bulky and decomposes rapidly). Plant high biomass covers in late summer and fall where you will plant late spring and summer crops, as you will have plenty of time to "terminate" them and watch them decompose before planting. Low biomass covers are good as winter cover where you will plant early spring crops (like peas and brassicas) or in spring and summer where you will plant again within a couple of months or so, as they will break down quickly upon termination.

Perennial cover crops are beneficial in areas that you intend to let fallow for a few years (some are short-lived perennials), and around large perennials, such as fruit and nut trees and berry bushes. I am rethinking my practice of keeping the area around my berry bushes and brambles clear. But not all perennial plants are good for this purpose and some may be detrimental. Do your research.

Cover crops also can break the cycle of some plant diseases and pests. For example, marigolds help manage crop damaging nematodes; grassy covers also break the cycle of certain diseases. Cover crops also can help break up compacted soil. Tillage radishes (the long-rooted daikon) and turnips are particularly good at this. Some cover crops also provide food or habitat for beneficial insects.

Crimson clover in bloom in late spring.

I can't cover everything about cover crops here, just the three I currently use. But I offer a couple of links to good resources on cover cropping. Most cover crop resources focus on large scale agriculture, but that info can easily be adapted to gardens. You can buy a hard copy or download for free "Growing Over Cover." I have not yet read through this, but it is published by the Kansas Rural Center -- an awesome program -- so I trust that it contains great info. This cover crop periodic table also has great, easy to access info, plus additional slides that describe individual cover crops. And here you can either buy hard copy or download free Building Soils for Better Crops by the Sustainable Agriculture Research and Education program. This covers much more than cover crops, and again focuses more on large scale production. But healthy soil info can be translated to even the smallest garden plot, containers even. I have not read through this one either (but I've got it downloaded), but I see it referenced a lot when I'm doing research.

OK. The cover crops I use are oats, buckwheat and crimson clover.
-- Crimson clover is a legume, which fixes nitrogen. It does this by taking nitrogen from the air (where it is quite abundant but not usable by plants) and through a symbiotic relationship with bacteria converts it to a form that plants can use. When the plant dies (or you terminate it), nitrogen is returned to the soil. This is a high biomass, cool-season plant. It is my go-to for winter cover and early spring cover. It survives my winter when well established, so it grows again in spring and keeps the weeds at a minimum while fixing nitrogen. It's crimson flowers provide nourishment for bees and other pollinators. However, it's usually recommended that you not let cover crops set seed or they will reseed and become weeds themselves. I have not considered this a major issue, and because I don't always get around to things in the most timely manner, my crimson clover covers usually flower. They're beautiful.

--Oats is a grassy cover. Seed is cheap. It grows quickly and can be used throughout the season, even as a winter cover. While it winter kills when the temperature hits the high teens, it remains in place, providing cover and roots to keep the soil intact. I usually interplant it with crimson clover or buckwheat. Since it is a high biomass plant, I interplanted it sparingly with the buckwheat. You also can consider a patch of oats as homegrown hay mulch. If you let it set seed, you can harvest the grain at the "milky" stage for a great herbal medicine for soothing nerves.

Arugula self-sowed to become a cover crop in a bed where the beets and

carrots did not take.

--Buckwheat. No, it's not related to wheat at all. It's not even a grass. Buckwheat is related to rhubarb, dock and other members of the polygonium family. This warm-season cover can be planted mid-spring through early autumn. I've planted it in March and gotten very little germination, but planted in April and it grows thickly. Until the Master Gardeners' lesson on cover crops I didn't give buckwheat a second thought as winter cover. It is killed by temperatures in the mid- to upper-20s. However, because it is low biomass, it is great for planting where I will put my early spring vegetables. Buckwheat takes up potassium from the soil and converts it to a form other plants can use. It grows rapidly, so when planted about a month or so before your expected first frost, it makes a nice stand. It was the first of the three covers to sprout this fall. Bees adore buckwheat flowers and make a rich, dark honey, that works great in suppressing coughs from the nectar. A large patch of flowering buckwheat nearly roars with the industry of bees.

--Other plants not usually called cover crops can be useful here, as well, even some weeds, such as henbit. (Why weed it out then? Just let it serve you.) Definitely don't let these weed plants set seed, though. Also some leafy green vegetables and annual herbs can serve as covers, it they sprout thickly enough. Right now I have a cover crop of arugula growing where the spring crop dropped seed. The beets and carrots I planted there did not germinate well (too hot and dry), so I let the arugula take over. Not only will it remain there until some pretty deep cold, I can eat it, too.

When planting cover crops, keep the seed bed moist until significant germination occurs. Then water occasionally until they get well established.

I will say no more. Check out my links for much more information. Just get your assets covered.