Chapter 6

Cover Crops for Organic Farms

Cover Crops in Perennial Systems

Cover crops often are used in orchards, vineyards, and other perennial crops. Cover crops are an important component of organic orchard and vineyard floor management. The alley planting can be grass that produces biomass for mulch, a legume to generate nitrogen, insectary plants, or any combination. This method can reduce irrigation, weed control, and cost. Vineyards often use cover crops in alternate rows which are alternated the following season. The cover crop planted rows allow the grower to use machinery in the alley more readily during the wet season.

Cover Cropping Farming Systems

Choosing a cover cropping farming system will depend on the relative vigor of the site; water availability in the soil; farmng objectives (increasing or decreasing vegetative growth); and pest management objectives for insect, mite, and weed control. Following are discussions of several different approaches

Annually Tilled and Seeded

The majority of growers using this system choose it to conserve moisture in their orchards and vineyards. Cover crops are planted in the fall, allowed to grow until some point in the spring when the ground can be easily cultivated, and then mowed and tilled into the soil. This operation is often timed when the cover crop is flowering, as it will decompose easily at this stage

Non-tillage Floor Management with Annual Cover Crop Species

In a no-till system with annual cover crops, the orchards and vineyards are tilled initially and seeded with species that will reseed themselves on an annual basis. Thereafter, the orchards and vineyards are mowed in spring and early summer. Tillage is restricted to only beneath the vines. Subterranean clovers, rose clovers, crimson clover, red clover, berseem clover, bur medic, bolansa clover, and Persian clover are all suited for this farming system.

Non-tillage Floor Management with Perennial Species

Perennial species are most commonly used in orchards and vineyards planted on fertile sites. Many of the perennial grasses are very competitive with tree or vine roots, and will have a devigorating effect on the orchard or vineyard.

Tilled and No-till Farming Systems

Some growers use different farming systems in alternate tractor rows to moderate vigor, incorporate compost, provide diverse habitat, or for aesthetic reasons.

Self-reseeding Cover Crops

Many tree and vine crop growers prefer to use self-reseeding annual cover crops. Using these species can reduce or eliminate the costs associated with purchasing and sowing seed each year. Although many of these species compete effectively with weeds if properly managed, in some cases the reseeding cover may revert back to resident vegetation within a few years. It may be necessary to resow the cover crop in three to five years.

Challenges in Growing Cover Crops In Perennial Systems

Considerations when choosing orchard or vineyard cover crop are discussed in the following sections.

Water Use

Cover crops use water and will increase the total orchard or vineyard water requirement. In spring, cover crops can deplete stored soil moisture from winter precipitaiton that would otherwise be available for the trees and vines.

Risk of Frost

A bare, firm, moist soil orchard or vineyard soil absorbs heat during the day and releases it at night, increasing the air temperature by as much as 3 to 4 degrees F (1.6 to 2.2º C).

Tree and Vine Vigor

Cover crops can reduce tree and vine vigor, which can be either an asset or a liability, depending on available moisture, tree and vine size, and available nutrients. In cases where tree and vine growth is vigorous, dense sod-forming grasses such as turf-type tall fescue and perennial rye grass may be grown to reduce excessive tree and vine growth.

Shade Tolerance

Cover crops usually need to be shade tolerant when used in perennial systems. Cover crop mixtures often do best in the varied light environment under perennial canopies, as each crop flourishes in the areas best suited for it.

Click on the following topics for more information on cover crops for organic farms.