Winter Protection in the Vineyards

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Winter protection of our plants is required for some varieties of grapes we grow here at Pheasant Ridge Vineyards. In the winter of 2003-2004 the fall season was in the normal too just below normal in temperature range. When December got here the daily high temperature was 30 degrees above normal. I was out pruning on January 4th in shirt sleeves; it was 64 degrees. As I pruned I noticed that the plants were getting sappy from the abnormal temperatures for this time of year. The following day the temperature dropped to 17 degrees below zero. That was an 81 degree drop in a 24 hour period. We lost a lot of our plants, some did recover but we knew that we needed to do something to insure against these harsh temperature swings.

With Vinifera grapes winter damage can range from bud death to the total loss of the plant. The bud of a grape plant is located at the base of each leaf. Each bud has three embryonic shoots that can push out the following growing season. Each bud is covered by scales and tiny hairs. If you make a transverse cut through the bud, you can see the three compact new shoots inside. The largest is the primary bud which will produce the best grapes. The next largest is the secondary bud. It will produce some fruit but less than the primary. The smallest is the tertiary. The tertiary usually does not produce fruit, only vegetation.

Bud death can be devastating to a grape grower. On grafted plants one can have a renewal shoot push out from the non differentiated cells of the graft union. If the graft union has been damaged, the plant will have to be replaced. Grapes that are growing on their own roots can send up new shoots from their roots. New shoots from the roots can grow to be very large in diameter. These shoots are called bull canes and are not optimal as renewals because the buds are not very hardy. The grower should choose a shoot the size of a pencil up to the size of your little finger to use as your renewal cane. If one only has a single bull cane it is best to top the shoot just below the fruiting wire to stimulate side growth which will be smaller in diameter and is more likely to have the buds survive to produce new fruit producing shoots.

The following are grapes varieties we grow here at Pheasant Ridge Vineyards. The table below is from the research of the late Dr. Bob Pool at the Geneva Research Station. All temperatures are in degrees Fahrenheit. The temperatures listed are the temperatures for which each variety sustain 50% primary bud damage. There can also be damage to the cambium of the trunk of the plant. These temperatures cannot be displayed since they vary with the amount of moisture present in the wood at the time of these severely cold temperatures. These damaging temperatures depend upon the temperature before a severe cold snap and are highly variable. Mild weather raises the trunk damage threshold, conversely colder weather makes trunks less seseptable to damage during a cold snap.

If one is fortunate enough to get a trunk renewal shoot, it could take up to two years before the plant will produce fruit. If the plant needs to be replaced, it will be three years before one gets any fruit. It is the cold clear nights when one gets air temperatures low enough to damage the buds. The trick is to protect the plants from that cold night air, which usually only lasts for a few minutes to an hour.

Earlier, in the late summer of 2003 I had hit a young Cabernet Franc plant with a front end loader on a tractor and knocked it off the trellis. I told myself repeatedly to stand it back up, but I never did. Fortunately we got about 1 inch of snow just before the arctic blast arrived on January 5th 2004. The only Cabernet Franc that made it through the winter of '03-'04 was the one that I had knocked down to the ground. The following year we decided to do a test. I took the same Cabernet Franc plant and tied it down to the ground. The winter of 2004-2005 was not as harsh as 03-04 but it was bad enough; we had a lot of bud damage. When I brought up the plant, I had tied down, we noticed that it still had good primary buds and it went on to produce a very good crop.

The following year the winter of '05-'06 we tied down all of the plants, it was a hard job that took six men 22 days to complete. We also bought a small sidewalk snow plow with a V blade snow plow attached. We modified the blade to fit between the rows and plowed the snow over the plants that were tied down to the ground. A sidewalk snow plow is a small track-driven machine generally used to clear snow from sidewalks by municipalities. We live in the snow belt of Central New York and we get on average 120 inches of snow a year. By covering the plants with snow we isolated them from the killing temperatures of the cold night air. According to Mr. Tom Zabadall of Minnesota State University, one inch of snow is equal to 27 degree temperature rise. With large snow depth the ground never freezes. The ground temperature can be 35 degrees while the air temperature is -20 degrees.

Vinyard Snow Plow	Plants Tied Down for Winter	Snow Plowed Rows

The plants stayed dormant and were held at about 20 to 25 degrees throughout the winter season. When the spring of '06 came we brought up the plants and we had most of our primary buds but noticed that we still had some bud death. We then realized that the buds that had died were only where side growth had been pruned off close to the vine, the ones that had a spur left did not die. During the summer months the primary shoots need to be topped when they reach the top of the trellis. When this is done the bud at the base of the leaf will begin to grow. This growth is the side growth or lateral shoot. A new bud will form at the base of the lateral growth. We believe that water soaked into the plant which damaged the buds where the lateral growth had been pruned off too close to the vine. This past year we pruned all side growth off at 2 inches away from the vine. As of February 15th of '07 our Cabernet Franc primary buds look very good. See photo at right...click on image for full size view.