Now Featuring

06/01/2011

The Cycle Continues: Flowering and Fruit Set

Although all farmers have at least one eye on the weather at any given time, the months of May and June are particularly tense for California’s wine grape growers. This is the stage of the growing season when grapevines flower and set their fruit, essentially setting the stage for the size and quality of the year’s crop.

“The weather is critical this time of year,” says Neil Roberts, owner of Roberts Vineyard Services, which farms 2500 acres in Paso Robles, Monterey County and Edna Valley, and proprietor and winemaker at Clavo Cellars in Templeton, CA. “You really don’t want it to be too cool, rainy or windy because it can disrupt pollination and fertilization.”

Depending on the weather and the grape variety, grapevines will start to flower approximately ten weeks after bud break. (If you drive by a vineyard in a car, however, you won’t necessarily notice the vines are in bloom because the flowers are so small; you have to be pretty close to notice the tiny yellow petals at the tips of the vine shoots.) White varieties such as Chardonnay and Sauvignon Blanc usually flower first, followed by Pinot Noir and then Bordeaux varieties such as Cabernet and Merlot.

Once the grapevines have flowered pollination and fertilization can take place. Grapevines are self-pollinating, so bees and other insects don’t play much of a role, but prolonged cool weather, rain or wind can prevent the flowers from pollinating completely or cause them to be fertilized unevenly – which can mean the fruit clusters will be sparse, uneven, or in the worst case, non-existent.

Flowering is almost immediately followed by fruit set, when the fertilized flowers develop into berries with seeds. Those flowers that didn’t get fertilized fall off during this stage, and again, the weather is crucial in determining how the clusters form. The term “shatter” refers to the condition that occurs when flowers don’t pollinate and don’t become berries, or when the berries fall off soon after forming. This results in what is known as a “poor fruit set.” Some varieties, such as Pinot Noir and Merlot are more sensitive than others to wind or cool, rainy conditions, and therefore more susceptible to shatter.

Fortunately, California is usually blessed with good weather during the May/June timeframe. “We look for nice sunny days and cool nights,” says Neil, who notes that (again) depending on weather and varietal, flowering and fruit set lasts between two to four weeks. “The ideal daytime temperatures are between 75°-90° F., and if we don’t get wind or rain, we consider ourselves lucky.”

While there’s not much that growers can do about the weather, there’s still a lot to be done in this vineyard this time of year. Vineyard crews are suckering and shoot thinning to ensure each vine is in balance in terms of the ratio of (potential) fruit to vegetation. Cover crops need to be mowed and/or disked into the earth, and the vines need to be fertilized.

Then there’s what Neil calls the “holy grail” of wine grape growing: estimating how big the crop that year is going to be. At this time of year, the process involves counting clusters on a select group of grapevines, multiplying that by what the weight of the clusters will be (based on varietal averages and historical bunch weight data from past years), then multiplying that by the number of grapevines in any given block or vineyard.

“Figuring out the crop size is important because it affects so many subsequent decisions, such as what kind of labor you’ll need at harvest, what returns you can expect from your vineyard, what the wineries can expect in terms of grape loads, etc.,” says Neil. “But being accurate is far from a perfect science. Weather conditions during the summer and at harvest can dramatically affect our yields, as can other factors such as grape-loving birds and animals. Mother Nature always has the last say.”

Photo Credit: Mora Cronin and Paraiso Vineyards

Photo Credit: Paraiso Vineyards