One of the most frequent vineyard questions people ask is how warm winters and springs affect the budding grapevines.
The Vitis vinifera that makes up most of the European grape varieties you have ever heard of are not as “spring sensitive” as the local flora of America. We graft those familiar European grapes onto a distinctly more Americanized rootstock, however. Vitis ripiria, V. rupestris, and V. berlandieri were hybridized with V. vinifera for the past century to give the grapes a resistance to insects and disease below the soil. Still, in Virginia USA, our grapevines do not wake up as early as the blackberry bushes and pear trees.
In two decades, I have never seen my grapevines bud out before the first day of spring. The first week of April is the norm, but for those of you who want an easier gauge to remember, look for the east coast Redbud trees blooming purple-red as the more accurate indicator the grapevines are also budding out.
Why do we care? Because the grape-clusters-to-be are already inside those little buds. Once the buds break, a cold snap or frost can kill them, and their potential grape crop. Very bad for your winery’s volume. It increases the cost of your bottle of wine.
Why do they bud out? Warm soil gets the roots pumping water – transpiration – up the trunk, out the arms, and to the canes. Water pressure. The warmer it gets in spring, the higher the pressure. That pressure first swells the buds bigger, then helps them erupt with a set of leaves. This pressure is greatest at the very ends of the canes, so the buds the farthest from the roots break out first. But not all the buds break out down the cane. The first breaking buds release a hormone called auxin that inhibits the next lower bud. After six or seven buds, all the lower buds don’t break out much at all. Left to themselves, the grape clusters would only form on the ends of the vines. In the wilds, before we domesticated them, these would be the vines that had grown the tallest up other trees and brush. The grapes would then ripen up in the sun where the birds could see them. Quite often in the ancient world, docked trees would keep the grapes off the ground and away from wildlife, livestock, and hungry children. The typical visual of an overgrown grapevine covered pergola has a basis in this fact. We pesky farmers needed grapes where they were easier to tend in a modern vineyard.
So, we prune the grapevine canes back to just a few buds every winter. Now the buds that break in spring are right by the trunk and arms in a range where it is easier to concentrate our sprays, energy, and labor to tend them.
Many trees and plants have a sap that can heal wounds like a scab. Grapevines do not.
With the root’s water pressure of a warming spring, our grapevines pump out water through the xylem tubes to the buds. But we’ve severed that cane, and the sleeping vine of winter did not seal it off. The cut vine begins to drip water in the coming spring. We call it weeping. If the vigneron stupidly makes big cuts on a vine, it can easily “weep” to death. When done right, this weeping is more tears of joy. The vines are awakening. The new season is beginning. The grapes are coming.
On this first day of spring, I thought you might like to see what a walk through the vineyard shows. Some of us have been working from home for decades. Our home office is just a little different than others.
May all the pressure you feel at this odd moment in an arriving warm spring, and all the tears for the loss we all share, remind us we’ll grow through this pain and past this hurt. We always have.