Winter injury is a serious concern in areas where subzero temperatures are more common. Native and French-American Hybrid vines generally will make it through a cold winter without issue but most premium wine grapes are of the cold sensitive species Vitus Vinifera. This is unfortunate for us northern growers, but it is not a show stopper. By applying modern viticultural techniques, these vines can be grown successfully in climates with relatively harsh winters and are common in the Finger Lakes of NY, Michigan, and even Ontario, Canada
Vine Selection
Before even starting, it is important to select varietals that have a chance of winter survival in your climate and are capable of achieving suitable ripeness. Some of the more successful wine grapes in colder regions include Cabernet Franc, Pinot Noir, Blaufranksich, Riesling, and Gewurztraminer. These vinifera vines are generally grafted onto American rootstocks for Phyloxera resistance and some control over vine vigor.
French-American Hybrid grapes are gaining traction as premium wine contenders. Popular choices include Marquette, Noiret, Traminette, Vidal Blanc, and Seyval Blanc. These generally have much better cold hardiness, disease resistance, and can be own-rooted or grafted. Before making your decision, make sure to try wines at your local wineries and see what tastes good in your region. The climate will have a significant impact on the level of ripeness achievable and flavor profile. A Columbia Valley, Oregon Cabernet Sauvignon will taste much different than the same wine made from Sonoma County Grapes.
As a rough starting point, here are some estimates of the cold hardiness of various grape varieties. One winter night below these temperatures is likely to cause some damage. In some cases, you could lose the entire vine which is why it is so important to use winter protection techniques.
Cold Hardiness Estimations for Common Grapes:
Cabernet Franc: -10°F
Pinot Noir: -5°F
Blaufrankisch: -5°F
Merlot: 0°F
Cabernet Sauvignon: -5°F
Riesling: -10°F
Gewurztraminer: -5°F
Marquette: -15°F
Noiret: -15°F
Traminette: -20°F
Vidal Blanc: -15°F
Seyval Blanc: -20°F
Concord: -25°F
Site Selection
If you live next to a lake or large body of water that doesn't freeze in the winter, you are in luck! South facing slopes on the north side of lakes offer many advantages, which generally include good sun exposure, nice airflow and air drainage, adequate water drainage, and protection from extreme cold. The lake acts as a large heat sink, warming the cold nights in the winter. As an added benefit, the cold water will cool the warm days in the spring, reducing the chance of bloom before the frost risk is over.
If you don't live by a lake, the top priority would be water drainage and south or west sunlight exposure. When vines have wet feet, they can be more prone to winter injury and exibit too much vigor to contain. They can also produce large grapes, with a poor skin to juice ratio which is a concern especially for red wines.
When planting on hillsides, remember that cold air drains down the slopes and settles in the valley floor. Try to select your site at least 1/4 to 1/3 of the way up the hill. This will provide nice airflow to discourage mildew and botrytis and will give a few degree temperature bump to help ripening and winter protection.
Slowing Down the Vines
It is important that the vine growth is able to naturally slow down as winter approaches. This allows the vines to store much needed carbohydrates and to harden the green wood into bark covered wood. To encourage the vines to slow down, don't fertilize or apply compost after mid season (~July). Irrigation should also be halted unless the vegetative growth shows obvious signs of stress and wilting (This is rare in cool regions). A cover crop can be grown to help compete with the vines for nutrients. Good cover crop options would include, wildflowers, weeds, grasses, or clover. Depending on the vigor of the site and varieties, the cover crop may be trimmed, weeded, or tilled until mid season, then allowed to grow out. Depending on the cover crop, you may want to trim before it goes to seed.
Hilling and Burying
Now that you have done everything else right, it is time to do some active winter protection. A relatively simple strategy is to hill up the vines. Hilling up protects all the work that has gone into establishing a healthy root system in the event of extreme winter damage. To hill up is to bury the vine in a mound of dirt to several inches above the graft union. In the event of a total vine loss, the section of vine up to the top of the mound should survive. In the spring when the hill is removed, and the dead vine trunk discarded and one or more new trunks should emerge and rapidly grow back to the trellis. This will cause a loss of fruit for the year after the damage, but will save the vineyard in the event of a once-in-ten-years cold spell. Hilling up can be done by hand with a grape hoe, or with a modified plow on a tractor. Hills should be removed in the early spring, leaving the graft one to two inches above the dirt as usual. If severe damage or crown gall is evident, a new trunk (or two) should be grown from the healthy tissue below the hill.
A more extreme but very effective option is to bury the entire vine each year. This is easier when the vines are young and flexible. As trunks get older and thicker, new trunks can be grown from the base and swapped out. To bury the vines, dig a trench with your grape hoe, lay the vines in and cover with dirt. Make sure to mark the locations of each vine with a stake to make unburying easier. If you live somewhere with reliable, deep snow, the vines can be untied and buried under the snow for protection.
Hilling or burying should be performed after the fall frosts have sent the vine into dormancy and the leaves are mostly off.
Spare Parts
This technique is common in the Finger Lakes of New York. Often two or more trunks are retained at any given time. If one trunk suffers damage, it can be removed and replaced with a new younger trunk.
Other Considerations
In addition to winter injury, damage can also occur to early opening buds and young shoots if a frost occurs after growth has started. Some actions to help delay spring growth late pruning and removal of grow tubes in the fall. Late pruning helps to delay bud swell and should be performed in late winter rather than fall in cooler regions. Grow tubes can warm up the vine on a sunny day, causing a higher risk of growth before the last frost. For this reason, grow tubes should be removed before winter.
Summary
With modern techniques it is more realistic than ever to grow cold sensitive grapes in cooler regions. Most techniques are labor intensive and do not guarantee success, so consider growing a few cold hardy hybrids to ease your pain if damaging winter temperatures do occur. If you are planning a new vineyard, be sure to check out Starting a Backyard Vineyard: Part 1 and Part 2. Supplemental info can also be found for free on The Home Winemaking Channel.
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