Cover crops play an important role in the vineyard, but they don’t need to be fancy seed mixes requiring lots of time and water. A Washington State University viticulturist believes growers can take a “lazy” approach to cover crops and still reap all the ­benefits.

WSU’s Dr. Markus Keller showed his concept of the perfect cover crop during a summer juice and wine grape field day sponsored by the Washington Grape Society held in August. The native grass-broadleaf weed mix of the cover crop came up in Washington State University’s new eight-acre wine grape research plot this spring without seeding or irrigating. “This is my idea of a cover crop—we didn’t seed anything and we didn’t irrigate it to get it up,” he said, noting that they got lucky with a cool, wet spring conducive to growing grasses and broadleaf weeds. “We don’t do anything now in late summer to it except mow. You let grow what is adapted to your site.”

Keller added that the native grasses began coming into the well-worked-up field before the young vines were even planted this past spring. His vineyard manager wanted to kill the weeds and start with a clean slate, but Keller prevailed in his request to let them be.

The young vines are watered two to three times a week through drip irrigation, which seems to generate enough moisture in the alleyways to establish and keep the cover crop green. Keller isn’t exactly sure what perennial grasses are in the mix, but lambs quarter and nightshade were identified as a few of the broadleaf weeds.

“I don’t really care what is in the cover crop,” he said. “But what I care about is biodiversity and that the weeds are producing flowers. I want it to be green, be able to mow it, and not compete with the young grape plants.” He noted that if it goes dormant in late summer or fall, that’s okay.

In an older WSU Concord grape research plot also visited that day, Keller explained that he follows the same approach with the cover crop: doing nothing but mow. He showed growers a cover crop that started out similar to what is growing in the new research wine grape vineyard, but one that has changed over time. Now, the composition of the cover crop in the Concord block is mostly grasses, with just a few broadleaf weeds.

“Over time, if you don’t do much to the cover crop, it will adapt to your particular site,” he said, adding that perennial grasses do well in the area. He noted that they have had to spray out puncture vine weed from some areas of the cover crop.
Previous work by former WSU Extension educator Dr. Mercy Olmstead showed that a mix of crested wheatgrass, pubescent wheatgrass, and perennial ryegrass performed well in eastern Washington’s arid climate and sandy soils. Resident vegetation can be effective as a cover crop, if invasive, noxious weeds can be kept in check.