A Grapevine Pruning Tutorial with Viticulturist Jordan Lonborg and Vineyard Manager David Maduena

After four relatively quiet months, March is go time in the vineyard. The days start to get longer, the cover crops and wildflowers 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 with the cold weather we've seen this year, the grapevines shouldn't sprout for at least another few weeks. But all of a sudden you know the clock is ticking.

Normally, we'd prune starting in January. And we did get a bit of a start this year.  But it's been wet enough that there were lots of days where we couldn't get into the vineyard, and pruning in the rain is an invitation to fungal infections and trunk diseases. That means we're behind where we'd normally be. You can't prune too early, because you need to wait until the vines are dormant so that they can store up the necessary vigor in their roots. And 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, we typically do the bulk of our pruning 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. 

Viticulturist Jordan Lonborg and Vineyard Manager David Maduena took 90 seconds to explain what they aim for in their pruning, and then demonstrate:

Pruning at Tablas Creek Vineyard from Shepherd's Films on Vimeo.

All this is done by hand.  We have about 115 acres that need to be pruned.  80 of these acres are trellised like the ones in the video, at roughly 1800 vines per acre.  The other 35 acres are head-trained, at much lower density, between 350 and 600 vines per acre.  That's more than 160,000 vines to prune.  At 20-25 seconds each, that's slightly more than 1,000 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? Pruning our vines well 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 thirty.  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.

We estimate that we're about 70% done with our annual pruning work. This week is supposed to be sunny, and if that holds, by the end of the week we should be largely done. And then we have another little break where we wait for budbreak and get to start worrying about frost. As I said a few years back, springtime is terrifying... but hopeful.