To Prune Now, or Prune Later?

Weather predictions and the historical record affect decisions in the vineyard, including when to start pruning
Dec 21, 2009

We’ve had relatively warm and beautiful weather here for the past week. The hills are green and, with the absence of cold weather, the grass is growing. The last storm two Saturdays ago dropped slightly less than an inch of rain. The ground was already producing runoff before the major storm hit and I was happy that it did not drop the forecasted 2 inches-plus of rain that was predicted by the National Oceanic and Atmospheric Administration. The storm had a subtropical air-mass associated with it and the potential to create erosion.

With the short winter days, despite the week of mostly sunshine and quickly growing pasture, I am still feeding cattle and probably will be for at least another month. The new grass does not have enough nutrients or energy that the cattle need to provide milk for the calves at their side and for breeding. To describe the need to feed despite the presence of green grass, the old cowboys would say, “The new grass doesn’t have any strength to it.”

In my last blog I tried to provide some insight on dealing with the potentially wet winter and also the fact that the conditions of the growing season vary in every vintage. As farmers, we are at the mercy of Mother Nature, and she is an unpredictable mistress. (Begging and pleading for mercy is to no avail.)

The only thing predictable about the weather is that it is unpredictable. This was driven home to me first by my grandmother and also by a weather study from my region based on tree-ring samples over the last 400 years of rainfall on a mountain 50 miles east of my location. There are very clear wet and dry cycles evident over various time scales, but embedded within every cycle there is a wide range of variability. With dry periods existing within wet cycles and wet periods within periods of lengthy drought conditions.

In many ways farming is like gambling, and Mother Nature is the house. In general, I try to implement practices that on a historical scale of “normal” weather conditions, during most years will produce the best quality fruit possible. But… there is the almost irresistible urge to use the climate and weather data that is available to adjust for the expected or current conditions and modify the specific practices implemented for exigencies and to hit the highest notes possible.

The first throw of the dice was this week. With the dry weather pattern setting up, I started to prune the vines two weeks earlier than the typical first week of January when we normally start pruning.

There are several reasons for starting early. If the winter is as wet as forecast, given the El Niño conditions in the Pacific Ocean, then we might not have as many days available to prune the vines as in normal years. We probably won’t be able to get into the vineyard to work on our normal schedule this year.

In addition, when pruning, I do not like to cut the vines during wet weather because the spores of various pathogens could enter the wound before it begins to heal. During periods of dry weather and up to several days before obvious rain, we cut the primary cane that bore the prior vintage’s fruit. Since we will probably have fewer sunny days, I am taking advantage of the current conditions for that first cut. We will clear the trellises of brush (last year’s growth) on those days before and after rainfall rather than cut, to minimize exposing the vines to spores.

Hanging over the decision of when to begin pruning is the knowledge that when pruning occurs will influence the timing of budbreak. Generally the earlier pruning begins, then by some internal clock of the vine, budbreak will occur earlier, carrying with it an increased risk of potential frost danger.

Balancing the risk of potentially earlier budbreak and frost is that during El Niño weather conditions with the slightly warmer ocean waters, the risk of late frost is greatly reduced. (Please Mother Nature, have mercy on me, your poor servant.)

Another factor that weighs in on this equation is that with higher levels of rainfall, the mass of the soil is greatly increased. The reason that this is important is that budbreak is greatly influenced by the warming of soil temperatures. With larger soil mass due to the increased water held by the soil, it will take more heat in order to shift the soil temperature upward. This will help delay budbreak.

And the cover crop acts as an insulator that keeps the sun from directly striking the soil and warming it. The cover crop will help delay budbreak as well, though will need to be carefully managed as it approaches.

Finally, after we have cleared the trellises of brush, we will still need to make a few smaller cuts as we go through and select the primary cane to tie down for this next year. This second cut, typically made in late February, helps to delay budbreak as well and because the sap is beginning to flow out of the pruning wound there is a much lower risk of infection in inclement wet weather.

Whoohoo! Here we go!

Harvest United States California Santa Barbara County 2009

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