Chronicles of a Dirt Farmer: On Bloom and Fruit Set


Every year around Beltane (beginning of May), the vines start to look rather leafy and verdant as the canes grow. Hidden in the canopy or sticking out awkwardly here and there are the clusters, little nibs of green on branched stems.*

When the shy buds unfurl to form leaves at bud break, it’s not too long after that the season’s clusters emerge. Formed the season previous, differentiating microscopically, they are coiled up and merely waiting for their time to unfold into bloom.

These last-year’s-clusters grow on the shoot just below the first couple of leaves. Bud break sees one, two, three, maybe four leaves, then the tiny clusters behind them. They grow quickly, however, stretching and expanding daily. Within a little under two months, they grow from less than millimeters to sometimes over 15 centimeters long, ready to set fruit.

fruit set

credit Debby Zygielbaum

The weather in May is of particular interest to us grape growers as the conditions need to be just right to ensure that the flowers set fruit. Grape flowers are self-fertile, meaning they can pollinate themselves, and are wind pollinated, meaning they do not need to attract insects, and are consequently little green, nondescript affairs. (Even so, I’ve still seen the occasional bee, covered in sweet-smelling, yellow grains, lustfully rolling around a cluster or two.) Like any other fertilization process, the pollen grains need to make it from the anther (male parts) to the stigma (female parts); it’s not terribly far, but a few climatic occurrences can wreak havoc with the process. Too much wind blows all the pollen away. Too cold and the pollen can’t grow down into the flower ovary. Too wet and the pollen can’t float to the carpel. Sometimes the fruit sets, but the little cap of the flower, known as the calyptra, doesn’t open and fall off, but stays stuck to the top of the berry. This can cause scarring which could be later entry points for botrytis.

So much can go wrong. Every year, as the little green nibs open to petal-free, yellow-anthered blooms, as the air fills with the light, sweet fragrance of grape blossoms, I am practically holding my breath watching the weather. This year, because of the dry winter, those fragile flowers emerged early – towards the end of April rather than the middle of May.** It’s more likely to have inclement weather towards the end of April, so we were all tense. But even though it was a bit wet, the clusters managed to set most of their fruit.

Whew. Made it through the second hurdle towards harvest for one more year.
*The main stem of the grape cluster is known as the “rachis.” The parts holding the flowers (and later the berries) to the rachis are known as the “pedicels.”

**This year, bloom was 10 days earlier than average. And I’ve been running to stand still ever since – which is why this essay is at least a month and a half late.


Debby Zygielbaum is the Vineyard Manager (or, as she’s fond of saying, ‘Dirt Farmer’), at Robert Sinskey Vineyards in Napa and a frequent contributor on Nopalize. She can be found @walkthevine on Twitter and Instagram.