It's verasion for the early varieties here at Rist Canyon Vineyards. Most growers would be thinking of harvest but knowing the winters that we can get here in the Rocky Mountain Foothills, I'm already thinking of getting the vines through to the next growing season. I'm lucky here though. At this time of the year it is very dry. I have to irrigate and because of that, I have control over what the vines will get for moisture. It's at this time of the growing season that I begin to cut them off. Lack of moisture leads to
cane maturity. It also helps the fruit ripen properly. To me, it is imperative that the fruit ripens, is harvested, and there is still time for cane maturation. The vine needs time between harvest and the first frost to obtain the maximum hardening to make it through the winter in the best condition. Right now, bird nets are up and I'm awaiting the new crop. It's time to think about what's going to happen between now and winter. At this point, the base of the canes are beginning to take on a different color. The hardening process has begun. With most early varieties, the hardening begins at verasion. But it takes beyond harvest for total maturation to occur. You can relate to the late year when harvest was followed by an early frost. The canes looked like they were ready to go through
the winter but come next spring, dead wood. Just because the canes have changed color, you can't always depend on them to make it through the winter in perfect shape. The hardening process is caused by both daylength and decreasing temperatures. This is when the canes form a periderm and bark. They seal off the moisture within the vine. The more time the vine has between harvest and the first killing frost, the more hardened the canes will be. The vine also begins to deposit carbohydrates in the canes at this time. The sealing off of the canes and the accumulation of carbohydrates will ensure the survivability of the vine over the winter. By the first frost, the vine should be able to withstand temperatures below freezing. The first frost and temperatures below 20F start the second phase of winter hardiness. This is the acclimation process. Acclimation allows the vine to "supercool". Supercooling allows the vine to survive sub-zero temperatures and survive until spring. Varietal differences and the year's growing season both affect the overall winter hardiness of the vine.

At the Rist Canyon Vineyards, I try to optimize this process by irrigation control. Starting on the first of August, when I water the vineyard, I cut the amount water applied in half. The vines get the same regularity of irrigation with less water. This begins to stress them and put them into a hardening-off attitude. With verasion, I begin to irrigate less often. Instead of twice a week, I water only once (with the reduced amount of water) weekly. This not only hastens cane maturity but the fruit ripening too. Thus allowing for an early harvest and plenty of time for the canes to harden properly by the first killing frost.

When to harvest is one of the toughest decisions the grower has to make. Each variety needs to be harvested in its own time. Determining when that time is can be tricky. You must take into account not only the sugar content of the grapes (brix), but also the total acidity and the pH of the juice.

One last note: Grape ripeness should be evaluated by more than one factor. I use Brix and pH because these can be evaluated quickly using a refractometer and a pH meter with a limited amount of berries. But you should also take into account characteristics that don't need to have any instruments to evaluate. Ripe grapes have certain textures, smells and other attributes. Ripe grapes also detach easily from the stems versus unripe grapes. The seeds of ripe grapes are usually dark colored. It's the vineyardist that will take all these characteristics and measurements into consideration when he/she decides to harvest the crop.

We would love to hear what you think of this issue of Rist Canyon Vineyards Grape Growing Newsletter. And of course, if you have any suggestions for upcoming issues that you'd like to share with us, please send those, too!
Just email me at: ristvin_jrb@ristcanyonvineyards.com