What is a living mulch
Living mulch is a cover crop sown in the same area as a vegetable. This practice is also known as undersowing and has only recently begun to be used in vegetable crops. Not all cover crops are suited as living mulches.
Why use a living mulch
Living mulches reduce weeds, protect soils from erosion, and provide significant organic matter to be incorporated into the soil. Living mulches are new tools in the sustainable grower's tool kit. In some cases, the residue left behind by a living mulch have an adverse effect on certain soil borne diseases.
What cover crops can be used as a living mulch
No one living mulch fits all situations. You as the grower must get acquainted with your particular situation including your soil type, pH, the main crop you intend to undersow, and the particular habits/needs of the cover crop you intend to use.
Not all crops do well with living mulch undercover. It is very important for the characteristics of a living mulch to complement those of the main crop. Living mulches should germinate and grow in the shade and be low growing relative to the main crop.
Vine type cover crops should be used only with tall vegetable crops (such as sweet corn) because they will climb and over-take lower growing crops. Bush type cover crops such as red clover should be used on shorter vegetables such as cabbage, peppers and determinate tomatoes. Cover crops should not be susceptible to the same diseases as the main crop, and should not interfere with harvest.
Cover crops are typically divided into 2 classes: legumes and non-legumes. They are categorized this way to indicate those cover crops that produce high quantities of nitrogen (legumes) that can be made available to the soil after the cover crop dies.
Legumes:
White Clover: White clover is an excellent choice for a living mulch cropping system. It is shade tolerant, withstands traffic, grows fairly low, and survives repeated mowing. White Clover must be managed to avoid competition with the main crop for nutrients, light and moisture.
Red Clover: Red clover is a dependable, low-cost, readily available workhorse that is winter hardy in much of the U.S. (Hardiness Zone 4 and warmer). Easily overseeded or frostseeded into standing crops, it creates loamy topsoil, adds a moderate amount of nitrogen, helps to suppress weeds and breaks up heavy soil.
Hairy Vetch: Few legumes match hairy vetch for spring residue production or nitrogen contribution. Widely adapted and winter hardy through the warmer parts of hardiness Zone 4, hairy vetch is a top nitrogen provider in temperate regions. Hairy vetch generates an abundant biomass that can be both a benefit and a challenge. A stand of over wintered vetch will smother spring weeds and can help you replace all or most nitrogen fertilizer needs for late-planted crops.
Cowpeas: Cowpeas are heat tolerant and, in fact, thrive in hot, moist climates. Cowpea varieties have diverse growth habits. Some are short, upright bush types. Taller types are more vigorous and better suited for use as cover crops as they put out vines and climb well. Cowpeas protect soil from erosion, smother weeds and produce 100 to 150 lb. nitrogen per acre. Cowpeas generate dense residue that helps to improve soil texture but breaks down fairly quickly. Cowpeas have excellent drought resistance combined with good heat tolerance. Low fertility and a range of soils make cowpeas viable throughout the temperate U.S. where summers are warm or hot but frequently dry.
Field Peas: High nitrogen fixers, field peas produce abundant vine forage and contribute to short-term soil conditioning. Field peas produce succulent stems that break down easily and are a quick source of available nitrogen. Field peas grow rapidly in cool, moist weather.
Non-Legumes
Oats: Oats are a reliable living mulch that winterkills in Hardiness Zone 6. Oats provide quick, weed-suppressing biomass, take up excess soil nutrients and can improve the productivity of legumes when planted in mixtures. Oats have a fibrous root system. Oats are an upright, annual grass that thrives under cool, moist conditions on well-drained soil. Oats can reach heights in excess of 4 feet.
Buckwheat: Buckwheat is an excellent short-season cover crop. It establishes, blooms and reaches maturity in just 70 to 90 days. Buckwheat residue breaks down quickly. Buckwheat suppresses weeds and attracts beneficial insects and pollinators with its abundant blossoms. Buckwheat is easy to kill, and reportedly extracts soil phosphorus from soil better than most grain-type cover crops. Buckwheat thrives in cool, moist conditions but it is not frost tolerant. Even in the South, it is not grown as a winter annual. Buckwheat is not particularly drought tolerant, and readily wilts under hot, dry conditions.
Annual Rye: Ryegrass is a quick-growing, non-spreading bunch grass, annual ryegrass is a reliable, versatile performer almost anywhere, assuming adequate moisture and fertility. Ryegrass does a fine job of holding soil, taking up excess nitrogen and weed suppression. Ryegrass is also an excellent choice for building soil structure in orchards, vineyards and other cropland to enhance water infiltration, water-holding capacity or irrigation efficiency.
Rapeseed (aka: Canola): Canola is a quick growing cover crop that decomposes quickly when tilled under. Rapeseed is a very good crop for nitrogen fixation. Rapeseed plants grow 2 to 4 feet tall. Rapeseed is good for weed suppression and may help suppress diseases such as Verticillium wilt and Rhizoctonia.
Comments
Living mulches will compete for water and nutrients so it is essential that they be managed carefully so as not to negatively impact the main crop.
Because the use of living mulches with a main vegetable crop is a relatively new practice, it would be worth your time to experiment with different cover crops.
It is not uncommon to sow a mix of cover crops as a living mulch.
Drilling the cover crop seeds instead of broadcasting will significantly increase the germination rate of the seed.
References
Sustainable Agriculture Research & Education program (SARE), Managing Cover Crops Profitably, SARE.
Peet, M., Dr., Living mulches, Sustainable Practices for Vegetable Production in the South, North Carolina State University, http://www.cals.ncsu.edu/sustainable/peet/cover/l_mulch.html, Accessed 2003-01-17.
Coleman, E., (1989), The New Organic Grower, Chelsea, Vermont, Chelsea Green Publishing Company.