back

Going"Native"With Vineyard Cover Crops

If you asked the average north coast vineyard manager to list the top ten sustainable farming practices out there, 9 out of 10 would probably mention cover crop programs in their first breath. As we have become more educated in agricultural land stewardship and called to accountability for conserving our non-renewable soil resources, how we farm between the vine rows is becoming increasingly important. Soil erosion control, weed suppression, improving soil structure, controlling vine vigor and encouraging beneficial insects and spiders are all good reasons to farm for cover. Practical farming considerations aside, many wine grape growers are also interested in creating an aesthetically pleasing "sward" in the vineyard.

Growing cover as a green manure, where annual weeds or Fall-seeded plants are turned into the soil each Spring, has been practiced here since the beginnings of the wine industry. We need oceans of yellow mustard in our valleys to appreciate one of the first cover crops introduced for soil enrichment. As hillsides became a more common setting for wine grapes, introduced European annual grasses and clovers became the first of the "no-till" cover crops to be managed without a disk. In 1985, the USDA Soil Conservation Service (now the NRCS), found that the average acre Napa Valley hillside vineyard was eroding at 5 to 7 times the tolerable replenishment rate. No-till cover crops were found to be the single most important tool for sustaining soil productivity, and still are today.

As no-tilling has become increasingly common for erosion control, growers are also discovering that bonuses accrue as well. Energy savings realized when the disk is retired from service, and firmer wet weather footing are well recognized and appreciated, particularly in an El Niño season. Many growers also report fewer insect and mite problems when cover residue is left on the soil surface. Potential draw-backs include competition between the vine and cover crop, and creation of conditions favorable to rodent pests such as gophers and meadow voles. Indeed, time and experience have shown that carefully selected cover species and floor management techniques need to be adapted to each individual vineyard micro-environment.

One of the more exciting recent advances in the science of no-till has been the discovery that native perennial grasses, which once flourished in our hills and valleys, can be returned to vineyards as managed cover. If we could journey back to the days when elk roamed freely, and the grizzly bear reigned supreme, a closer look at the north coast landscape would reveal bunch grasses waving in the breeze under oak trees, and native sods accenting seasonal wetlands and streambank edges in hues of green and gold. Surely the land will never fully return to those landscapes, but what an interesting thought that plants such as these, with such a long history of adaptation to local soil and climate are proving to be a natural, effective choice for cover crops. Exercising a little patience, and putting a little more management input into the equation, more growers are beginning to appreciate the endurance and tenacity of native grasses.

What Are They ?

Probably the most commonly planted grasses are Meadow barley, California brome, and "Molate" red fescue. Meadow barley and Cal. Brome are most at home on deeper, more fertile soils with good water holding capacity. Both of these plants establish fairly readily (not a common trait for many of the perennial grasses). Molate exhibits moderate seedling vigor and appears to be more adaptable to a variety of sites and conditions. Another native commonly sold in mixture with Cal brome and Meadow barley is Blue wildrye.

These 3 in combination provide a fairly vigorous cover. You may want to go with this mix if irrigation water is plentiful and the vines can stand a bit more competition to balance out vine growth with the crop. Several other grasses to consider are Pine bluegrass, California barley, Idaho fescue and Purple needlegrass. These grasses are a little trickier to get established in a vineyard, but are showing some well balanced growth and summer dormancy characteristics that may make them a more welcome addition to the vineyard.

Testing around the state, including plots studied here in the Napa County by the RCD, seem to indicate that native grasses extract moisture from the soil profile at a slower rate than some of the introduced annual covers. Perennials will draw some moisture a month or so beyond annual covers, but don´t appear to pull down late Spring moisture levels to the degree that the opportunistic annuals do. Unless irrigated with sprinklers, most of these cool season perennials will also go dormant with the onset of dry, hot summer weather.

Whatever your choice of native grass, consider adding some native wildflowers to the cover blend. These plants fill in the gaps between bunches of grass and provide a nice opportunity to attract beneficial insects and spiders to the vineyard. They also are pleasing to the eye!

A few key management principles should be followed in making the conversion to no-till natives:

· First and foremost, develop a seedbed that is as weed free as possible. Many of the weeds we fight today, and even the plants introduced for cover crop and pasture use, did battle with these natives for many years and certainly have the upper hand.

· Plant as early after harvest as possible and don´t get too anxious for results. These grasses establish slowly in the first spring and will definitely not show the initial vigor of an annual cover crop.

· Once established, don´t get too agressive with the mower. Mow in the later Spring when seedheads have matured and keep the mower cut high (about 4 to 5 inches), to avoid scalping the crown of the plant.

· Where compatible with the vineyard, consider applying light amounts of nitrogen in mid spring to give the grasses a bump

· If the cover appears to be too aggressive, think about alternate row mow and tillage. If this doesn´t pose a problem with erosion control needs, it can do wonders to take a little pressure off the vines and still provide many of the benefits of a no-till system!

· If wholesale conversion to natives seems a bit risky, set aside a portion of the vineyard to try it out. Give the cover and vines a chance to readjust to the rooting environment. It may take several years to fully judge the results, so try to be patient.


(written by Phill Blake)

back