Science of Wine: Cover Crop Part I

1/27/2016 11:20:55 PM

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I ONCE HEARD A COMEDIAN SUGGEST that the perfect thing to say to sound like an expert while swirling a glass of wine is “The rains were good that year.…” It got a laugh from everyone in the club that night, but what makes me laugh is the idea that the rains are ever simply considered “good” in any year. In 2013, for instance, there wasn’t enough rain. The 2010 rains were poorly timed. Now, in the winter of 2015-’16, erosion is a concern. Good or bad, we don’t just roll over in the mud and throw our hands up. The committed winemaker plants seeds in the mud — and prays for good weather.

Erosion control is a hot topic this season, and winter cover crops — plantings that help manage erosion and improve soil quality — are a natural way to address it. At Palmaz we carefully study individual locations within the vineyards to assess their needs at the moment, as well as identify potential problems that might emerge later in the year. Our NDVI data assists in making this determination. Different locations in the vineyard have different needs; determining which plants can best meet those needs in the time we have to work is part of the art of winemaking in the winter.

A few things to keep in mind about cover crops:

They have a limited amount of time to do their job before the grapes retake the stage. A cover crop shouldn’t compete with the primary crop in a vineyard — that is, the vines. Therefore most are planted after harvest, then either mowed over or tilled under just as the vines are budding the new shoots. Cover crops must be rapid growers and hardy in order to do their work in the cold months of November through March.

Soil stability is paramount. Though less than a half-inch of steady rain falls on most winter days, the occasional two- to four-inch rainstorm can wreak havoc in the vineyard. A landslide can destroy our life’s work in a single moment.

Competition can be a good thing. Some plants, such as legumes, help add nutrients to the soil, thereby promoting the vines’ growth later in the year. When the vigor of the vines is too high, however, competitive plants — such as grasses and wheats — will deplete the soil a little and help control canopy growth in the summer.

Some change can be a good thing, too. It’s inherently risky to grow one crop for five decades or more on a single piece of land. In a vineyard, cover-crop rotation to promote soil health is limited to the spaces between the rows. Careful handling and subtle changes are therefore necessary.

For more, including a look at specific kinds of cover crops, see the next post. -CGP