By MARION BARNES
Senior Colleton County Extension
For home gardeners planning to give their garden plots a rest this fall, planting a winter cover crop now will benefit next summer’s vegetables.
A cover crop will protect the soil from erosion during the winter, suppress weeds, maintain soil moisture, increase organic matter in the soil and recycle nutrients. Improving soil organic matter is key to improving soil health, which makes nutrients available to plants. Cool season cover crops form a living mulch during winter and act as “green manure” when plowed down in the spring before planting.
Cool season cover crops can be terminated with herbicides and left on the soil surface in a reduced tillage system. Although this type of tillage system can prove challenging for home gardeners, commercial farmers use it extensively.
Planting dates will depend on what type cover crop you plant but generally, cool season cover crops should be planted around mid-to-late October in the Coastal Plain in order for plants to become well established prior to a killing frost.
Before planting a cover crop, gardeners should determine the goal for planting the cover crop. Is nitrogen needed for the next crop? Do weeds and nematodes need suppressing? Is additional organic matter need? Your goals will influence the type of cover crop you establish and its planting date.
Cool season cover crops can be divided into two groups: legumes and non-legumes. Legumes are plants that have the ability, if properly inoculated, to “fix” or transfer atmospheric nitrogen gas into “soil nitrogen” which is available to plants. Nitrogen fixation in legumes depends on Rhizobia, a group of common soil bacteria that invade the roots of legumes and form nodules. Often, specific Rhizobium species are not present in the soil in sufficient numbers to be effective in nodulating the roots of a specific legume. Inoculating the legume seed with the correct Rhizobia bacteria at planting will ensure effective nitrogen production. These bacteria are specific for different legumes and nitrogen fixation will be low without the presence of the correct Rhizobia bacteria.
Today, many legumes such as clover and vetch come pre-inoculated with the correct bacteria. When legume cover crops are tilled into the soil, crops that follow can benefit from the residual nitrogen left in the soil, therefore reducing fertilizer cost.
Legumes are an important source for providing nitrogen, but many cool season legumes can increase populations of nematodes, root-knot nematodes in particular. Some cultivars such as Cahaba White vetch and Cherokee or Southern Belle red clovers have shown promise in nematode management. Ongoing research indicates that certain brassica species release natural chemicals (glucosinolates) that show promise for the management of soil borne pathogens like nematodes. Plant-parasitic nematodes are prevalent in many home gardens, so it is important to have the nematodes identified and focus on their management.
Non-legume cover crops like rye, oats and wheat are planted primarily to provide biomass to the soil. This biomass — roots, stems and leaves — add structure to the soil, and water holding capacity.
Recently, brassica crops like daikon radish have become popular in cover crop mixes. Daikon radishes, sometimes called tillage radishes, develop long taproots that penetrate compacted layers of the soil, increase soil aeration and water infiltration. Nutrients absorbed by the large taproots decay quickly and are released in the soil for uptake by following crops.
Planting cover crops in a home garden is not with some challenges. In order to get the most benefits from cover crops, they need to be terminated with herbicides after significant biomass accumulation and/or plowed down as a green manure crop. These management practices require the use of herbicides, sprayers and heavy tillage equipment in most cases. Some home gardeners may not have access to these types of equipment.
Before planting a cover crop, evaluate your ability to manage a cover crop. As previously stated, legumes like clover can act as host to nematodes, which can be problematic for vegetable crops such as Southern peas and beans that follow in the spring or summer.
Non-legume cover crops like cereal rye contain lots of carbon relative to nitrogen, which causes them to decompose slowly. When large amounts of non-legume biomass, such as straw, is incorporated into the soil, they “tie-up” or immobilize soil nitrogen for a few weeks. Soil microorganisms take up nitrogen to balance the carbon in the residue during the decomposition process. During this time, garden plants may become nitrogen deficient. For this reason, it is suggested to wait a few weeks after incorporating a non-legume biomass like cereal rye before planting vegetables.
The proper use of cover crops will improve the productivity of your soil. If you decide to plant a cover crop for the first time, start small and experiment until you find the right mix for your situation.
For more information on planting cover crops in the home garden, check out the Clemson Extension cover crop fact sheet HGIC 1252 titled, Cover Crops.
For more information on growing vegetables in the home garden contact the Colleton County Clemson Extension office, 843-549-2595.