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nder-vine cover crops are managed plants grown underneath the rows of vines. Vineyard managers grow them on purpose to help achieve certain goals in the vineyard. I find them fascinating to talk about because their benefits and challenges are complex and never guaranteed.

Grape growers working with overgrown vines might bring in competitive cover crops to slow their vigor. Organic-leaning vineyards often use cover crops to suppress weeds in place of herbicides. Those on steep hillsides should think about installing cover crops to stop erosion. If the cover crop is selected and managed well, vineyard managers should find success with these goals for at least several years.

Other benefits are less straightforward. In some cases, cover crops might help increase soil organic matter and retain nitrogen, but the effects are often less that one might expect. Grasses tend to re-capture the nitrogen they put back into the soil after decomposition, so it may never reach the grapevines. Flowering cover crops will help attract pollinators like bees to the vineyard. This is wonderful as long as you are avoiding insecticides, which can kill those bees congregating around your flowering cover crop.

Growers considering cover crops should first decide what goals you want to accomplish. Then, learn which types of cover crops to plant based on what will help achieve those goals. For example, a simple perennial fescue mix works wonders for most goals – vigorous fescues can easily outcompete most weeds, slow excess vine growth for several years, and support soil structure while requiring minimal mowing. Flowering species can be incorporated if desired. Vineyards hilling up graft unions each winter should consider annual cover crop species because the soil is frequently disturbed.

Slow Down Overly-ambitious Grapevines

Is excessive vigor a problem in your vineyard? Are you constantly hedging and thinning to keep them under control? A strong, thick stand of undervine cover crops might help slow the growth of overly-vigorous grapevines. Plants with dense root systems like perennial grasses compete with grapevines for water, nutrients, and space in the soil. When those roots get established, they tend to take up so much space in the soil that the grapevine roots avoid the top several inches of soil. The top few inches of soil are often the richest in nutrients and organic matter. So, when the grapevine roots are forced out of this area of soil, it can cause the vines to grow more slowly as they have limited access to the buffet of top soil resources.

To use cover crops for vine vigor management, select a short, densely-growing perennial grass such as fine fescue. Wait to plant it until the vines are at least 3 years old, so that the grass competition does not stunt their early growth.

There are many fine fescue species to choose from. The species that I have personally worked with is creeping red fescue. Fine fescues are short, only growing about 8 inches tall, and only need to be mowed 1-2 times per season. These grasses are also effective weed suppressors because they form a thick thatch of grass blades along the soil surface, blocking sunlight from hitting the soil surface. During my graduate research on fine fescues in vineyards, creeping red fescue formed a dense tangle of roots in the top 10 cm of soil, forcing the grapevine roots to avoid that area and grow deeper into the soil.