CELLARS WINE BLOG
October 13 - Where does the time go? I've been so busy with my commercial vineyard project near Willcox that I just haven't had time to keep up this blog. There has been something on my mind lately, so here we go.
Last year at an AZ WineMakers meeting in early May one of our members gave a presentation on crop forcing. What is this you wonder? Well, grape growers have long known that an aggressive mid season pruning could prompt a grape vine to start over again, as if it is spring. Stripped of all of their leaves and pruned of excess vegetative growth, vines will go through bud break, flower, and fruit set.
Although long understood, few considered the potential of this technique to delay fruit set and harvest, thus increasing the quality of wine grapes when grown in an area considered too warm. If a particular variety only takes 5.5 months to go from bud break to harvest, but a region has an 8 month long growing season, pruning early to mid season can restart the vine and push back the most important phase of ripening into the autumn when temperatures are cooler.
Viticulture professor Dr. Sanliang Gu of California State University, Fresno, has really taken the lead on testing and developing crop forcing techniques. His tests have shown that by delaying fruit set and harvest in warm climates like central California, pH can be lower at harvest while still developing the desired brix. You can read more about his work here:
Intrigued by the possibility of improving the quality of my low desert wine grapes, I decided to experiment with crop forcing on a small scale. In mid May of 2013 I pruned a few vines like I would in the early spring. I did this with a Nebbiolo, a Cabernet Sauvignon, and a Syrah. I would like to tell you the results were great; unfortunately they were not. In fact, this experiment was a complete failure. Post pruning none of the vines thrived, growth was not vigorous, leaves were small, and clusters were few and small. I had to study on this for a while to understand what went wrong. The problem, I believe, was our intense summer heat. Grape vines do marginally well in the lower deserts only because the vigorous growth happens in March, April, and May, when daytime highs are not extreme. By pruning the vines in mid May I forced them to produce new growth, flower, and set fruit all in the hottest part of the summer, from late May through early July. They didn't have a chance in 2013, however, they have survived.
The trick, I believe, is to pick a variety with a shorter season, one that can go from bud break to harvest in less than 5 months and do the pruning around July 1st. The lower temperatures and higher humidity of the monsoon season should create a more friendly growing season for the vines and increase the chance of success. This is something I look forward to experimenting with at both my low desert hobby vineyards and my new commercial vineyard new Willcox. I am still intrigued, even if my first attempt was an unmitigated failure.