Viticulturist Levi Glenn and Vineyard Manager David Maduena demonstrate grapevine pruning

February is the month when the relative calm of winter ends.  The days start to get longer, the cover crops explode into growth thanks to the sun and rain, and it starts to feel like spring is just around the corner.  Of course, it's not, quite; it's still often below freezing at night, and the grapevines won't sprout for another month at least.  But all of a sudden you know the clock is ticking.

This is when we prune.  You need to wait until the vines are dormant to prune them, so that they can store up the necessary vigor in their roots.  But pruning too early encourages the vines to sprout early too, and in an area prone to spring frosts -- like Paso Robles -- that's a risk.  So, rather than prune in December or January, we prune in February and March, starting with the varieties that sprout late, and which we're not too worried about freezing, like Mourvedre and Roussanne.  We try to finish with Grenache, Grenache Blanc, and Viognier, which all tend to sprout earlier, in the hopes of getting another week or ten days of dormancy out of them. 

Two weeks ago, we had just started pruning the Roussanne and the Mourvedre.  Viticulturist Levi Glenn and Vineyard Manager David Maduena took a few minutes to explain what they aim for in their pruning, and then demonstrate on a couple of Roussanne vines.  First, the overview:

Then, they dive in, first Levi demonstrating how we choose which canes to leave and which to prune off, then David pruning a vine at full speed.  It takes him 23 seconds.

Yes, all this is done by hand.  We have about 105 acres in production.  80 of these acres are trellised like the ones in the videos, at roughly 1800 vines per acre.  The other 25 acres are head-pruned, at much lower density, typically 600 vines per acre.  That's about 160,000 vines to prune.  At 23 seconds each, that's about 1,022 man hours of work.  Figure that we typically have 8 of our full-time crew working on pruning in this season, with an hour of breaks each day makes 146 days of work... or with a crew of 8, just over 18 work days each.  That sounds about right... roughly a month of work, if the weather holds.

Why does all this matter? Having the correct pruning on our vines has several positive effects:

• It reduces yields and improves quality.  As a rough estimate, you can figure on one cluster of grapes per bud that you leave during pruning.  Leaving six spurs each with two buds predicts roughly a dozen clusters of fruit, which should give us about the three tons per acre we feel is ideal for our setting and our style.
• It makes for a healthier growing season.  If we space the buds correctly, we should have good vertical growth of canes and have clusters of fruit hanging below the canopy.  This configuration means that air flow through the rows should naturally minimize mildew pressure.  It will also shade the fruit from the sun at the hottest times of day, while allowing any nutrients or minerals we spray onto the vineyard to penetrate the canopy.
• It promotes even ripening.  Different vines in any vineyard block have different base levels of vigor.  If left to their own devices, some might set a dozen clusters while others might set forty.  Of course, the more clusters, the slower they ripen.  Getting an even cluster count helps minimize the spread between first and last fruit ripe in a block and makes the job of the picking crew much easier.
• It sets up the vine for the following year.  Done well, pruning encourages the growth of wood in places where it will be needed in future years, filling in gaps where cordons may have died back in previous years or separating spur positions that have grown too close.
• It saves labor later.  A good example of how much labor good pruning saves can be found by looking at a frost vintage, where the primary buds have been frozen and secondary buds left to sprout wherever the vine chooses.

So, we've been spending February giving the vineyard its winter haircut, while we hope for continued frosty nights that will delay the day when the vines will sprout to begin the 2012 growing season, and we get to start worrying about frost.