John Marshall: Tips for Getting Grapes Ripe
It seems like only yesterday- well last year- when we saw conditions like this; a chilly spring, no heat to bring the buds along and a late blossom which got our crops off to a very late start. The only difference is that a year ago most of us had very heavy crops, which were approaching September like a huge freight train charging full speed toward an open draw bridge. Lots of crop rushing day by day toward disaster (frost).
This year is much the same except that the freight train we are all caring for is, for the most part, much smaller. It also seems like the chances of seeing summer warmth linger into mid-October again, as it did in most areas last year, to be beyond possible expectations. Last year, in mid-October, after picking one of the largest overall crops we ever grew here along the Upper Mississippi River, and by far the latest we ever picked as well, I love to tell people I felt like I had experienced a miracle out of scripture. We had harvested one of the largest, latest and ultimately best crops we had ever had. What are the chances of that scenario repeating itself?
Even so there is reason for hope. It is important to recall that, in general, we have a much smaller crop to ripen this year. Therefore, the crop is likely to reach at least acceptable levels of ripeness earlier than a larger crop. In fact, I noticed one thing last year that surprised me: Although the crop dawdled into July last year before serious development really began, I noticed that by August, the crop began to look ripe and the berries seemed to be fairly soft, even if the acids were still off the charts.
The sugar readings we began to see this year were climbing as well. My neighbors up the road picked their Frontenac very close to the same day as in a more “normal” year. Although I doubted that it was a good idea to pick, it eventually occurred to me that the vines were reacting to shortening day length and the crop was coming along faster than anticipated. This scenario- smaller crop responding to reduced day length- remains entirely possible, if not almost inevitable this year.
Moreover, there are some simple and fairly cheap measures you can still take this growing season to bring the crop along. One is leaf removal. Removing basal (first leaves from the cordon) brings clusters and developing fruiting buds into sunlight. It is of critical value on VSP trained vines This is a cultural technique that can be used every year but surely can be recommended in this late year.
Another worthwhile technique would be applying a foliar spray of KDL (Potassium, Dextrose and Lactose) as close to veraison (first color) as possible. This is the time when the vine’s need for potassium is greatest and ripening is difficult in the presence of a potassium deficiency. While we are generally past true veraison even here in Minnesota, the grapes continue to require high levels of potassium during ripening.
While a foliar Potassium spray may be redundant in soils with abundant potassium, and may even create a magnesium deficiency if too much is applied, many Midwestern soils are chronically low in potassium. If you have struggled with potassium deficiencies in the past, a foliar spray of KDL will almost certainly benefit your struggling crop.
One important point is that some winemakers are convinced that grapes treated with potassium will encourage the development of proteins that will prove to be unstable, causing all sorts of winemaking problems. However, Katie Cook, the former Project Leader for the University of Minnesota’s winemaking project, carried out a study in which vines were treated with KDL at veraison at several concentrations, as well as unsprayed or control vines to test for any signs of increased instability. Her study, carried on for several years, failed to show any instability problems with foliar applied potassium at veraison. This study also indicated this technique did not create instability in finished wines.
A local manufacturer of foliar sprays recommends applying KDL about two weeks prior to projected harvest. They have found through comparative studies that this technique will often bring sugar levels up 2-3 degrees brix at harvest, compared to unsprayed control vines. This could be extremely valuable in a season when ripening is late and sugars lagging.
In a warm year with normal sugar levels, this technique might give the grower extremely high sugars. Ms. Cook’s study did not cover foliar potassium applied so close to harvest and so was unable to make conclusions about the value or safety of this technique. However, she did feel that in a normal year when sugars would be more or less normal, pushing up the sugar levels might well make the wines high with alcohol and not improve the final wine. In a year like this one, a late application of foliar potassium might be of enormous, even critical value to the final crop.
In any case there are number cultural techniques available to growers to bring your crop in at acceptable levels of ripeness. Aggressive leaf removal can provide important ripening advantages that can still improve ripening. Application of foliar potassium at or shortly after can improve ripening and does not endanger the final wines. For crops that are running seriously short of sugar, private studies have shown that foliar potassium applied closer to harvest can also push ripening along.
Needless to say, early frost can cut short the growing season and end ripening. However, recent experience has shown that both foliar potassium and Kocide, a well-known fungicide, when applied as close as 24 hours before frost can offer important protection to crops from impending frost damage. If your crop is threatened by a premature frost event that will cut short growing season there remains cultural techniques that offer the grower some hope.
Thus it is important not to believe we are at the mercy of a climate we cannot control. The crop your vineyard now carries are not anonymous grapes out of the deserts of California or waiting to be replaced by a truck of juice that will make wine available at any liquor store. You have a crop that offers individuality and special characteristics wineries still need. There is still hope to bring in a crop that your pocketbook, your winery, your customers, your region badly needs.
John is a regular columnist in Midwest Wine Press and a vineyard and winery owner in Lake City, Minnesota. See Great River Vineyard and Nursery for more information.