One of the most important rules of gardening is to always be gardening. That doesn’t mean we need to keep ourselves in the garden every working day planting, weeding, fertilizing, or harvesting. What it does mean is to have something growing as much of the year as possible. It also means to have something growing on as many square feet of our soil as possible. God designed soil and plants to work together. Soil cannot remain healthy without plants anymore than plants can remain healthy without soil.
Many people, when they think of cover crops, envision a cereal grain such as rye planted in the fall after the garden is harvested and tilled under in the spring before the garden is planted. While this is certainly a valuable and viable use of cover cropping, we will benefit from taking a little broader view of the concept.
Let’s look at some of the various benefits of having something growing in the soil as much as possible. First, keeping the soil covered with plants greatly lessens the danger of erosion. While this is a much greater problem in some areas than others, water will move practically any soil. Growing plants slow down the movement of water whether coming in the form of rainfall or running across the ground. Slowing the speed of water movement lessens the amount of soil it will carry with it. Plant leaves intercepting rainfall greatly slow the impact of rain and prevent it from compacting the ground. This is actually a bigger factor than many people realize. A heavy rainfall on bare soil packs the top couple inches/cm even if the ground is level enough to not significantly erode.
The soil’s biology is highly dependent on the plant community growing in the soil. Both the species and the amount of bacteria and fungi change based on what is growing in any given area. Soils devoid of living plants undergo rapid declines in their biological populations. Generally the greater diversity of plant life we can grow at any one time and place, the healthier the soil is likely to become. This is why having a few weeds growing in a corn or bean field is likely better than having a perfectly clean field between the rows. Diversity of microbes is much less important in perennial plantings of berry bushes or trees. Where one crop will be growing for many years, the biological life will reach equilibrium with the species growing and both will benefit as long as there is enough mineral nutrition to grow a healthy crop.
Another important function of plants is the provision of organic matter to the soil. Organic matter is very important in the structure of any good soil, and it comes entirely from living or decaying plants. Most times when we think of organic matter, we think of decayed plants or animal manure from consumed plants. Equally important, if not more important, to the health of soil is the organic matter that comes from living plants. This organic matter comes into the soil in the form of root exudates, which are sugars and amino acids that plant roots give off as they grow through the soil. Different species of plants have different formulations of root exudates; they stimulate and enhance different species of biology. Root exudates can be a very significant contribution to a soil’s organic matter. Any healthy plant, whether cover crop or a food crop, may exude over its lifetime as much as 50% of its total photosynthetic energy.
This means that if you have a healthy tomato plant that produces 20 pounds (9 kg) of plant above the soil, it will likely have close to the same amount of roots in the soil and can possibly exude about 20 more pounds of organic matter into the soil in the course of one season. These root exudates feed the biology that in turn digest the mineral nutrition and feed the plant. This cycle hinges on keeping plants growing as long as possible, because without living plants this cycle shuts down.
Another practical benefit of cover crops is maintaining habitat for various insects. We want to maintain a food source for pollinators at times when our fruiting crops may not be blooming. We also want habitat for carnivorous insects so they will be present in sufficient numbers to control harmful insects.
With all this in mind, what are some cover crop practices that yield results? As I already mentioned, planting a fall cereal grain to provide some cover in the off-season is a very positive thing. This should be considered the minimum. Greater things can be accomplished in terms of soil health and improvement by cover cropping in the growing season. This can be accomplished either by companion planting or by dedicated cover cropping a portion of your gardening area.
Companion planting is planting noncompeting plants within the same area. Whole books have been written on the subject, but I will give just a couple examples of combinations I have used in the past. Marigolds have the reputation of repelling several species of damaging insects. I often plant those within rows of tomatoes or cucumbers. I don’t know how effective they are, but they add some beauty if nothing else. Some late summer greens crops can be started down the middle of corn rows. The shade from the corn helps with the germination of cool-loving lettuce and other greens. This only works well after the corn is nearly mature and no longer needs a lot of water and nutrients. Various species of clover also work well as cover crops in corn. There is some debate among biological farmers whether it is worth seeding a cover crop between rows of corn at final cultivation when it is about knee high. Some farmers have observed that high-yielding crops tend to shade out the cover crops, but this issue will not be as likely in sweet corn.
It has been observed by biological growers that in-season dedicated cover cropping is so effective at increasing yields in the cash crop, they can dedicate up to one-third of their land for cover crops without lowering overall yield. My observation would concur. What makes growing in-season cover crops so effective is the biomass that can be produced. Winter cover crops typically do not produce a lot of biomass, and many of our garden crops also do not excel at biomass production per square foot. Biomass production is organic matter production, and that is what keeps the wheels turning for growing crops.
Particularly C4 plants such as corn, sorghum, sudan grass, etc., are very efficient producers of biomass. C4 plants can capture more carbon per water used than can C3 cool season crops. But, the C3 plants such as cereal grains still have a place in a rotation because they will produce biomass when it is too cold for the warm-loving C4’s to grow.
A typical full growing-season cover crop plan might be something like this. As early in the spring as the ground can be worked, sow a mixture of oats and peas. In early summer as the oats begin to head, work the crop into the soil and plant a mixture of heat-loving annuals. This summertime mixture can be quite diverse. I know farmers who are using twelve or more species in their summer annual cover crop. These include sorghum, sunflowers and other summer flowers, beans, tillage radishes, clover, etc.
The best summer mixtures will have lots of diversity and produce a lot of biomass before producing viable seed. Buckwheat is an old standby for a quick summer cover crop, but this basically is a “use by itself” crop. Buckwheat tends to smother everything else out and produces seed too quickly to use in a mixture. In late summer or early fall, we work n the summer cover crop before any of the annual species produce viable seed that could become a weed in the next season.
Following this, we have two choices for the winter. We can either plant a winter-hardy crop that will still be alive the following spring, or, in many areas, we can plant a crop that will winter-kill. Which is better often depends on the crop we plan to plant in the spring. Planting a winter-killed cover crop allows us to plant in the spring without having to worry about tilling in a cover crop enough to kill it. In fact, we may not have to till at all! Depending on the condition of our soil and the weed pressure that we face, it might be possible to plant some crops directly through the winter-killed mulch. This can also be an option later in the season with an overwintering cover crop. Again depending on the condition of your soil and weed pressure, it sometimes works great to roll down a thick stand of rye as it begins going into head and transplant crops like tomatoes, peppers, cucumbers, or squash directly through the flattened cover crop without needing to till at all.
Keep It Covered
