Growing grapes in Wisconsin is achievable, not as a casual gardening endeavor, but as a specialized form of viticulture requiring careful planning and specific techniques. Success in this state relies entirely on overcoming the geographical constraints of a continental climate, particularly the severity of winter cold and the limited duration of the growing season. Cultivating grapes here transitions to a focused exercise in maximizing genetic cold tolerance and implementing intensive vine protection strategies. This approach allows hobbyists and small-scale growers to produce fruit that otherwise would not ripen or survive the harsh climate.
Wisconsin’s Unique Growing Environment
The climate presents two primary challenges to traditional grape growing: the short growing season and the extreme winter temperatures. Wisconsin falls largely within USDA Hardiness Zones 4 and 5, with some northern regions dropping into Zone 3b, meaning the average annual minimum temperatures can range from -35°F to -10°F. These low temperatures are lethal to the dormant wood and buds of standard European grape varieties, which typically suffer injury below 0°F.
The short period between the last spring frost and the first autumn frost necessitates the selection of grape cultivars that can complete their ripening cycle in fewer than 160 days. Even classic American varieties like Concord, which require 155 to 160 days to ripen, only achieve full quality in the southern part of the state in two or three out of every five years. Beyond temperature, growers must contend with heavy clay soils common across the state, which can lead to poor water drainage. Waterlogged soil during the freeze-thaw cycles of winter is detrimental, as it can suffocate or damage the vine roots, making site selection that ensures proper drainage a top priority.
Necessary Cold-Hardy Grape Varieties
To circumvent the severe climatic limitations, successful viticulture relies on hybrid varieties specifically bred for cold tolerance and early maturation. These cultivars, often developed by programs at the University of Minnesota and Cornell University, are crosses between traditional grapes and native cold-tolerant American species, such as Vitis riparia. The genetic contribution from Vitis riparia imparts the necessary hardiness to withstand deep winter freezes.
Key red varieties include Marquette and Frontenac, which are reliably hardy to at least -35°F to -36°F, allowing them to survive winters with minimal or no protection in many locations. Marquette, a grandson of Pinot Noir, is capable of producing a dry, oak-aged red wine with notes of black currant and cherry. For white wines, La Crescent and Frontenac Gris offer significant cold tolerance and produce aromatic, high-acid fruit. Due to their cold-hardy lineage, these grapes often exhibit higher natural acidity, which winemakers typically manage through various cellar techniques or by producing sweeter wine styles.
Site Selection and Basic Cultivation
Careful site selection is the first and most defining step toward successful cultivation, as it directly modifies the microclimate the vine experiences. The ideal location is a gently sloping piece of land with a southern or southeastern exposure. This orientation maximizes sunlight and heat accumulation throughout the short growing season, which is crucial for ripening the fruit. Slopes are also necessary because cold air is denser than warm air and will flow downhill, preventing the cold air from settling around the vines and causing frost damage during spring and fall.
Soil preparation should begin the season before planting, focusing on ensuring deep and rapid water drainage, ideally in the top two feet. Grapes prefer a slightly acidic to neutral soil pH, generally ranging from 5.5 to 7.0, which may require amending heavy clay soils with organic matter or adjusting the pH with lime. Once planted, vines are best trained using systems like the bilateral cordon or cane pruning on a high-wire trellis, which provides optimal sun exposure and air circulation. Pruning is performed during the dormant season to manage the vine’s vigor and ensure that the remaining canes produce a manageable crop load that can fully mature before the first frost.
Ensuring Vine Survival Through Winter
Even with the hardiest hybrid varieties, protecting the permanent wood of the vine is often necessary to guarantee consistent yearly production in the coldest parts of Wisconsin. The most reliable and labor-intensive method involves physically protecting the canes and cordons from the extreme cold, particularly when temperatures drop below the vine’s genetic hardiness level. This process must be timed after the vine has entered full dormancy in the late fall, but before the ground freezes solid.
The technique involves carefully detaching the canes from the trellis and laying them flat on the ground. Growers then utilize the process of “hilling up,” where soil is mounded over the base of the vine and over the laid-down canes to provide a layer of insulation. For areas with severe cold or little snow cover, an additional insulating layer of straw or geo-textile fabric may be placed over the buried wood. The soil acts as an excellent insulator, maintaining temperatures just below freezing even when the air temperature drops significantly lower. The vines must then be uncovered and re-attached to the trellis in the early spring, after the danger of the deepest frost has passed, to allow for timely bud break.