5 Benefits of Planting a Radish Fall Cover Crop
The majority of backyard gardeners will not plant a fall cover crop. Though this practice is frequently used with overwhelmingly positive results by farmers producing cash crops, the benefits are yet to be widely recognized by the backyard gardening community.
One of the most beneficial rising stars in the world of cover crops is the radish. We aren’t talking about the garden variety, globe-shaped radishes; we’re talking about the open-pollinated, large-rooted, daikon-type radishes. You may recognize the form large, white, long radishes commonly used in Asian cooking. However, many of these culinary radishes are hybrids and prohibitively expensive, at least when being utilized solely for purposes of soil enhancement. The cover crop radishes we will discuss are not the products of formalized breeding and are relatively inexpensive. Not grown to be harvested, when used as a cover crop, these radishes will be left in the ground to die and decompose over the winter, with the beneficial results extending into the spring planting season:
Biodrilling is the name given to the robust growth, soil aeration and improvement of compacted soils of this root crop. Nature’s aerator, the roots of these radish plants can grow to more than three feet deep in as little as 60 days. The largest part of the root, what you may know as the tuber, can be more than one inch in diameter and extend more than 12 inches into the soil. Once the root withers, it leaves holes, often extending into the subsoil, which will improve drainage, and air and water infiltration. The biodrilling effect also improves the root growth of your spring-planted vegetables and even allows the roots better access to subsoil moisture, resulting in less water usage, especially noticeable when drought conditions exist. The naturally perforated soil dries out and warms up more quickly, enabling you to plant both seeds and plants earlier than normal.
Weed suppression is also a natural result of cover cropping with radishes. Studies have found that if you plant radishes early, at least 6 weeks before the first frost, and plant them in high concentrations, with at least five plants per square foot, weed suppression will be almost total into the month of April. This is not the result of bio-chemicals produced by the radishes, but is due, instead, to their rapid and weed-competitive fall growth. What that means for you is less preparation for springtime planting.
Nitrogen, Phosphorus and Potassium (NPK) production. Early springtime nitrogen, the result of radish residues, will give your vegetables an early growth boost. The nitrogen boost attributed to radish cover crops has been compared, by researchers, to that of planting a legume cover crop or of nitrogen fertilizer application. The result was shown to be most effective on sandy soils. Regardless of your soil type, however, planting a radish fall cover crop will save the time and money associated with a more labor-intensive cover crop planting and/or application of nitrogen-rich fertilizer. Radishes have also proven to be exceptional sources of P and K, further reducing your reliance upon commercial applications.
Soil erosion, runoff and organic matter are all improved with radish cover cropping. The leafy canopy, which can be established in as little as three weeks, significantly reduces the effect that rainfall, even if heavy, will have on surface impaction and subsequent runoff. Even after the radishes have been killed by a hard freeze, usually happening when temperatures drop into the mid-twenties, the layer of dead leaves on the surface throughout the winter and early spring serves to control erosion. Researchers also noted the water runoff and the resulting sediments were captured by the holes left by the rotting roots before it was able to leave the field. And though minimal, due to radishes highly decomposable nature, some increase in soil organic matter is inevitable.
Root knot Nematodes (Meloidogyne incognita), the parasitic culprit responsible for many vegetable deaths, especially the susceptible tomato, have proven to be sensitive to radish residues. Root knot nematodes’ numbers were found to be drastically reduced or completely obliterated. Researchers in eastern Texas planted radishes 58 days prior to planting sweet potatoes, with exceptional results. On the other hand, the beneficial nematodes, those which help to control disease and cycle nutrients to the plants (the ones we hardly hear anything about), were benefited by the nitrogen-rich radish decomposition.
All in all, the combined positive effects should result in a higher crop yield with less work for you. Cash crop farmers have long known the benefits of cover cropping with radish; we think it’s time you realize the same benefits.
Photos are complement of Josh Gruver of Western Illinois University and Ampac Seed Co.