Vineyardists have an array of cover crop choices, but the type of cover crop that works best will depend on overall vineyard management goals.
Choices range from annuals to perennials and from grasses, legumes, and forbs, to native vegetation.
Dr. Mercy Olmstead, Extension viticulturist for Washington State University, describes grasses as being beneficial in windy areas prone to soil erosion. Grasses tend to form large, fibrous root systems and provide important biomass that can help increase organic matter in the vineyard soil.
Cereal grasses like rye, oats, barley, and triticale are often used as annual systems, planted in the fall and mowed for stubble in the summer to reduce dust, compete with weed species, and provide traction for equipment.
Annual or perennial legumes are known for their ability to fix nitrogen in the soil, she said. Nitrogen is released from the plant and available for mineralization after the cover crop begins decomposing. However, moist soil conditions are needed for the nitrogen to be available to the plant. The large tap root system of legumes helps improve water infiltration, but on the down side, legumes also attract rodents to the vineyard.
Both annual and perennial forbs or broadleaved flowering plants are also available. The wildflower forb mixes can play an important role in attracting beneficial insects, but they can be difficult to establish if the plants are not appropriate for the vineyard region, she notes. Growers need to pay attention to all the species included in the flower mix as some mixes in the past have contained noxious weed species like yellow star thistle and purple loosestrife.
Annual choices for tilled vineyard
The following lists of annual and perennial cover crop choices that are best suited in a vineyard under tilled and no-till management systems were compiled by Olmstead.
Annual ryegrass—Cool-season bunch grass, useful in areas with excess nitrogen or water. Tends to perform better on finer-textured soils, although sandy soils may be adequate. Can compete with the vine during bloom and early shoot growth. Is typically seeded in fall and tilled in late spring or early summer.
Cereals (barley, oats, triticale, wheat, winter rye)—Can be interplanted with vetch. Triticale may outproduce other cereals in terms of biomass. Cereals have fibrous root systems helpful in reducing erosion. Planted in fall for winter moisture. Winter rye, cold tolerant down to
-30°F, is usually mowed in spring before the plant begins to senesce.
Field pea—Used as a winter/spring annual and tilled or mowed in early summer for its organic matter and nitrogen release. Stems break down quickly. Susceptible to winter kill without snow protection.
Mustards and Brassica species—Produces chemicals called glucosinolates that break down into isothiocyanide, which can act as a soil fumigant and weed suppressant. Sometimes grown and incorporated in soil before vines are planted. When grown in vineyard rows, should not be mowed until seeds have set. White and Oriental mustards have shown success in drier climates.
Vetch—Commonly seeded in stands alone or with cereal crops to provide stalks for climbing. Hairy vetch is prone to climb on vines and into trellises. Purple blooms on hairy and common vetch are attractive to beneficial insects. A continuous stand can be accomplished if vetches are allowed to reseed.
Annual choices for no-till
Clovers (subterranean, crimson, red)—Annual clovers often used in vineyards with no-till management. Subterranean clover has low, prostrate growth habit, while crimson and red species reach heights of six to eight inches. Clovers perform best when part of a mix and may be hard to establish in soils with poor nutrition. The hard seed that is produced by clovers will germinate over several years.
Medics (bur, barrel, and black)—Considered a reseeding annual or short-lived perennial. Bur medic does well in vineyards with little irrigation in rows if winter rains are adequate. Medics produce hard seeds, mature in midspring, and are easily controlled with mowing and herbicide applications.
Perennial cover crops
Fescues (tall, hard, red, sheep)—Can form dense mat of growth in vine rows. Excellent for weed suppression and traction. Well suited for dryland vineyard conditions, fescues will go dormant in summer without moisture, providing mulch layer. Should be seeded in fall. Prolific seed producers, but can be hard to eradicate.
Indian ricegrass—Native to western North America, often used for erosion control on sand dunes. Is a summer-dormant species that retains its hold on soil particles and useful for sandy, windy sites. A cool-season species, ricegrass is drought tolerant.
Meadow barley—Performs best in wetland or riparian areas and can tolerate clay with low calcium and low water-holding capacity. Is a poor competitor with weeds, so take weed control measures before planting.
Perennial ryegrass—Cool season, moderately drought tolerant. Establishes quickly and germinates early, but can be competitive if overseeded. Good at providing erosion control due to its fibrous root system. In areas with cold winters, should be seeded in late summer.
White clover—Performs better on heavy soils than lighter, sandy soils because it’s not as drought tolerant as other clovers. May require replanting every three to four years. Plants hardy to 17°F.
Wheatgrasses (crested, standard crested, pubescent)—Known for their drought tolerance and persistent stand. Good at suppressing weeds. Can be seeded in combination with forb mixes.
Wildflower/forb mixes—Native flowers and grasses may enhance ecological diversity. Germination and persistence can be improved by choosing native varieties. Broadcast application, followed by a cultipacker may be necessary for seeding.