Overcoming cold-climate challenges(2)
If vine size and balance are important to successful winegrowing in cool and cold climates, then soils, too, must be important. Thirty years in viticulture have proven to me that from the Mosel to Alsace, Burgundy, Bordeaux, Piedmont and elsewhere, small vine viticulture produces the best wines—reds in particular. This is a controversial topic, but I would generally observe that if a terroir can be found that supports small and balanced vines (i.e., well-drained, low-fertility soils and modest, timely rainfall—or lack of it), then lower yields per vine can help to promote and even accelerate fruit maturity.
The key is soil moisture, whether it is measured as plant available water or total available water. Getting the vine to change gears from vegetative growth to fruit-ripening mode is tremendously important in all climates, but much more difficult in cool and moist ones. Small to medium vines require soils that are well to excessively well drained and have low to moderate nutrient levels, along with other size-regulating feat ures such as soil pH, cation exchange capacity and organic matter. These are the same requirements for fine wine production in warm regions that, at least in theory, should impart similar effects on vine behavior and fruit quality in cool and cold areas.
Many vineyards will be planted on soils that do not have optimal drainage or fertility, so other means will be necessary to impose balance on the vines. These may include choice of rootstock, cover crops, vigor diversion methods, severe hedging and divided canopies, to give just a few examples. In warm and dry years vine performance will be manageable, but in cool, wet years, wine quality and cold hardiness will be more difficult to achieve. In cool/cold vine cultivation, growers should plan for the worst conditions and be grateful for the occasional fine vintages.
Soil is always at the heart of site selection, but there are many other important secondary considerations that comprise a good site. In selecting a site in a cool to cold region, the grower is attempting to lower the risk of a frost or freeze event that will compromise wine quality in any given year, good or bad.
If bare soils help with frost prevention, it seems likely that stony soils will assist even further by gathering heat during the day and radiating it at night. The shale soils of Pennsylvania’s Lehigh Valley may offer this advantage. Other favorable site characteristics include convex landforms, slopes, correct aspect and local and absolute elevation. Among these, local topography may be the most important factor for avoiding frost/freeze, and avoiding low spots in the vineyard may be the single most important feature a grower can seek when selecting a site. Cold air and water accumulate in low-lying areas, and both increase frost/freeze risk and hamper vine acclimation. Even virtually imperceptible depressions in a field can cause problems. There are many cases when low-lying vineyards sustain damage while mid- to upper-slope sections are unharmed.
If low spots should be avoided, placing vineyards on slopes should be encouraged. This motivates both air and water to flow away from the vineyard, thus lowering frost/freeze risk and encouraging fruit ripening and vine acclimation. Some growers seek sites with up to 30% slope, but almost any amount of slope will help. Absolute elevation will have an impact on the risk of frost and/or freeze events. Higher elevations are generally cooler and will delay fruit ripening and possibly raise the risk of winter injury. In warm macroclimate regions, a higher and therefore cooler mesoclimate vineyard site may be preferable but increase frost and freeze danger—yet another compromise. Avoid trees and anything that may impede the flow of air and water off the vineyard site. Shrubs and brush at the bottom of slopes should be removed so that a clear drainage path can be made.
Aspect may be less important for frost and freeze, but in general a southeast to southwest orientation is preferred in cool- to cold-climate regions. In Europe, the further north the vineyards are, the more highly prized a south aspect becomes. Row orientation is ideally up and down a slope and north-south to northeast-southwest.
An important trellis design feature is fruit wire height. Lower height encourages ripening in the growing season but increases frost and freeze risk. There are arguments about the relative virtue of single vs. multiple trunks. The latter is the traditional method in cold regions, but some claim the additional stored carbohydrates may increase early season vine vigor. Winter injury is extremely random, and it is very possible that on a vine with multiple trunks, one may be damaged and the other(s) unharmed. Compromises abound and risk tolerance enters the decision-making process. I encourage the use of multiple trunks in cold regions, with the Mason-Dixon line being the border between safe and sorry.
Bud break delays
Once the site has been selected and the vineyard designed and installed, then the viticultural practices will have impact on susceptibility to frost and freeze events. Anything that can be done to ripen the fruit faster and, to some extent encourage later bud break, will help to avoid injury. Can rootstocks help the cause? There are certainly indirect effects of rootstocks that may help a vine to resist cold injury or delay bud break. A pioneer grower in the Endless Mountains is experimenting with Riparia R-39 (selected within the Arctic Circle) and ES1553 (an Elmer Swenson selection) that he hopes will directly impart cold hardiness to the scion. Certainly Riparia Gloire, Slate Quarry Riparia and other devigorating rootstocks may help the vine to ripen fruit earlier and acclimate better. More research would be very welcome in this area.
Two growers in northeastern Pennsylvania have experimented with dormant oils to delay bud break, following recommendations from the University of Nebraska. One said he had good results while the other’s results were negligible, but the number of applications appears to affect the results. Growers also claim that prophylactic applications of copper have helped. In California, products such as Frostgard are used. It is difficult to quantify the efficacy of many of these measures; it is likely that the “feel good because I’m doing something” effect is probably at work here.
Double pruning is another traditional method for gaining a few days of delayed bud break. It is important to note that anything you do to delay bud break will exact a price at the end of the season—likely with a later harvest date as a result, with its inherent risks and concerns. Yet another compromise.
Clean vine materials are important to cool- and especially critical to cold-climate winegrowing. Crown gall is a serious problem in cold-climate vineyards, and every effort should be made to find certified crown gall-tested nursery materials. Under marginal conditions, maintaining a healthy vine free of viruses and the assortment of trunk diseases will greatly enhance the ability of vines to survive. Plant the best quality nursery stock possible.
Mark L. Chien is statewide viticulture extension educator for the Penn State Cooperative Extension based in Lancaster, Penn.
