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Lifecycle of a Vineyard: How Grape Flowers Timing and Leafing Effect Harvest

Flowering chardonnay grapes in May 2016.

In the world of grape growing and vineyard management, the abundant fall harvest is generally what springs to mind. But the stages leading up to this yearly bounty are crucial factors to success. Grape flowers, or grape “flowering” in vineyard manager parlance, arrive in late spring, 40-80 days after bud break, depending on the temperatures and rain. To make their welcomed appearance, grape flowers need average daily temperatures to stay between 59-68 degrees Fahrenheit, generally sometime in May in Sonoma County. It’s during this stage of a grape’s lifecycle that pollination and fertilization occurs, with the results ultimately producing a cluster. To learn more about how spring weather influences bloom and fruit set, watch this fruit set video.

For fertilization to occur, unlike many other plants, the bees don’t have to buzz in the vineyards. Grapevines are hermaphroditic – they possess both male and female parts so, barring weather issues or pest invasions, grape flowers can transform into berries all by themselves. Read more about this process and the geeky science behind flowering.

What Can Affect a Grape Flower?

Jordan Winery Estate Petit Verdot grape flowers

Every vineyard manager wants an even fruit set, defined as when the fertilized flowers develop into a grape and then into picture-perfect clusters. But if the delicate grape flowers are exposed to rain, wind or cold temperatures, the dream of a beauty-pageant cluster can be dashed. Low temperatures can freeze the flowers or a heavy rain can wash them off. This unwanted result is called “shatter,” meaning the cluster grows without the ideal, tight shape with the berries differing in size. While this variation thankfully doesn’t affect the quality of the berries, it definitely affects their quantity. This article offers a photo gallery of various fruit sets and what a shattered cluster looks like.

Jordan Winery Estate grapes fruit set

Once the tiny berries appear, we begin our leaf pulling or thinning practice. This crucial activity allows for increased air movement within the vine’s canopy, as well as helps manage light penetration through the vines. The breezes help keep non-beneficial pests at bay and the dappled light helps prevent sunburned grapes which can negatively affect a wine’s flavor. To learn more about our leaf thinning program here at Jordan, watch this video: Leaf Vineyards to Prepare Grapevines for Ripening.

With the right practices and if Mother Nature cooperates, grapevines thrive, especially in the temperate and normally predictable weather of California. We’re fortunate to grow vineyards here but we pay a lot of attention to everything to maintain the highest quality standards. We know it shows in the bottle.

Brent Young

A 2005 harvest intern who returned to Jordan full-time as viticulturist in 2008. Now Director of Agricultural Operations in charge of estate vineyards, precision farming and cattle. Spends free time showing cutting horses and restoring vintage cars, especially Woodies.

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