Dormancy is an important stage of the grapevine annual cycle when growth and development stop temporarily and the vine rests. It is brought on by low temperatures and shortening day length. At this time, growers prune the vine and set it up for the upcoming season. Riesling fruit zone, grapevine and clusters at the Northwest Michigan Horticulture Research Center after fall frost, Oct. A review of growing season parameters. Growing season length is a critical parameter for vineyard site selection, and coupled with management practices, determine the ultimate success of the vineyard.

Eric Stafne, Mississippi State University

This article will answer the following basic questions:

• How do I plant a grape vine?
• What is the best time of year to plant grapes?
• When should I plant grape vines?
• What kind of plant material should I buy?

Planting Method for Bare-Root Vines

1. Be sure to keep vines moist right up to planting.
2. Dig a small hole with a hand-held or tractor-mounted post digger about 6 inches in diameter, 4 inches to 6 inches deep. In soils with high clay content, glazing of the sides of the hole may occur, which can impede root growth. In this situation, break up the glazed areas using a shovel or equivalent tool.
3. Immediately prior to planting, trim the roots to fit the hole and cut the top growth back to only two to three buds (above the graft union on grafted vines) on the strongest cane. Remove all other canes.
4. Stand the plant in the hole and pack the same soil back into the hole around the plant. If you are using grafted vines, make sure the graft union is above the soil line by approximately 6 inches.
5. Install a stake next to the vine to provide stability.
6. Water the vine with two or three gallons of water immediately after planting.
7. As new shoots begin to grow, watch for signs of pest damage that may inhibit vigorous growth.
8. Do not allow weeds to grow near the vine row, and keep the young vines well watered. The amount and frequency of irrigation will vary depending on region and environmental conditions.

Green growing (potted) vines should be acclimated to seasonal weather conditions in a protected area for a few days prior to planting. Do not plant potted vines until after the risk of frost has passed in the spring. Be sure to remove the vine from pots before planting. If you are using grow tubes, install them after planting, lightly covering the base with soil to exclude herbicide sprays. Do not bury them too deep into the soil as root constriction may occur.

Timing

Grapevine Fall Season 1

In most of the U.S., the best time to plant grape vines is very late winter or early spring, if irrigation is available.

To ensure the highest quality vines and a specific cultivar or rootstock, order vines from a reputable nursery [1] in the summer or early fall prior to planting in spring. If you wait until January or February to order, you could have problems with plant availability and/or quality [2]. For example, you will probably miss out on the best rooted cuttings (often termed #1), and poor quality vines can be too weak to survive. The nursery should ship the vines at or near your desired timeframe around planting.

Once delivered, vines should be planted immediately, if possible, and not stored. Storage of dormant vines leads to desiccation of the roots and buds. This will prohibit the vine from growing optimally and may lead to death.

If vines are received before the site is ready for planting (e.g., soil preparation, irrigation set up or trellis construction has not been completed), unpack the vines and cover them with soil in the shade until planting. This is known as “heeling-in.” Vines will remain healthy in the heel bed for up to four months. Do not store vines in water or a refrigerator for long periods of time. Water the heel bed periodically to keep the roots moist but not wet. Never allow the roots to dry out, as this will lead to poor growth or vine death.

Nursery Stock and Standards

Most grapevines are sold as dormant rooted cuttings and are either grafted or own-rooted. Rooted cuttings are graded by nursery industry standards. Becoming familiar with these standards is important to help you make decisions on plant material and can make the difference between success and failure of a new vineyard. For further information see Quality Guidelines for Grapevine Nursery Stock.

A 2-year-old #1 vine is more vigorous and will transplant with better success and become productive quicker than a #2 vine. A #1 rooted cutting is produced in a phylloxera-free nursery and certified as virus tested. Although certified virus-tested vines are initially more expensive, they are cheaper in the long run as this avoids problems with lower production and poor plant health associated with virus-infected vines. Remember, virus-tested vines from the nursery may not stay that way in the vineyard if efficient vectors are present, and virus-tested vines are not guaranteed to be completely virus free. Virus-infected vines can never be cured. Virus-tested cuttings should be ordered as far in advance as possible (up to one year prior to planting) to ensure availability of planting stock. Vineyard establishment from non-rooted cuttings is a gamble and you should consider success from them as atypical. This method, although less expensive initially, often leads to slower growing vines that do not come into bearing as quickly as purchased vines. You can also inadvertently introduce diseases and viruses into the vineyard by taking cuttings from another vineyard. All new vines should be free of viruses, insects, and disease.

Recommended Resources

Tips on Growing Grapes, University of Minnesota

Planting Grapes, Iowa State University

Growing Grapes, Ohio State University

Reviewed by Patty Skinkis, Oregon State University
and Keith Striegler, University of Missouri

Early fall frosts continue to encroach on the growing season. What does this trend mean for northwest Michigan vineyards?

Last year, the 2017 growing season was ended with low fall temperatures and fall frost before fruit was harvested, leaving the grapevines without a post-harvest foliated period. This year, a greater number of heat units were accumulated than in 2017, but sub-freezing fall temperatures were reached at an earlier date. What does this mean for vineyard operations, fruit quality and cold acclimation?

Because there has been very few additional growing degree-days (GDD) accumulating in the region since the sampling date (Oct. 16) and a vast number of regional vineyards have either partial or complete leaf fall resulting from low sub-freezing temperatures on Oct. 18, it is likely that any marked increase in sugar accumulation (Brix) is likely due to berry desiccation where the berries lose water and sugars are concentrated.

Pinot Noir in Leelanau County at harvest before fall frost, Oct. 16, 2018.

Riesling fruit zone, grapevine and clusters at the Northwest Michigan Horticulture Research Center after fall frost, Oct. 22, 2018.

A review of growing season parameters

Growing season length is a critical parameter for vineyard site selection, and coupled with management practices, determine the ultimate success of the vineyard. In past viticulture research from Jordan et al., 1980, the growing season has been defined as the number of consecutive days where the minimum temperatures are above 29 degrees Fahrenheit (-2 degrees Celsius). A more conservative and recent growing season definition from Jorgensen et al., 1996, uses 31 F (-0.5 C) as a temperature threshold below which frost damage will occur.

However, Michigan viticulture, like regions of Europe such as Austria, Germany and Burgundy, is classified by Perry and Sabbatini, 2013, as cool-climate viticulture with average growing season length ranging from 165 days (northwest region) and 180 days (southwest region), and is characterized by relatively short growing season length, cooler summers (relatively low heat unit accumulation) and potential frost or freeze damage during fall, winter and spring.

For this reason, frost-free days, defined as consecutive days with minimum temperatures above 32 F, are a more accurate and conservative determination of growing season length, and allow classifying sites as either unsuitable (less than 165 days), marginal (166 to 180 days), preferable (more than 180 days). By this definition and classification, Old Mission and Leelanau Peninsulas achieved 160 and171 consecutive frost-free days, respectively (Figure 1). This places the 2018 growing season length for the two peninsula AVAs in the unsuitable (Old Mission) and marginal (Leelanau) range classifications and this is due to early subfreezing temperatures in October (Figures 1 and 2).

Although the 2018 growing season accrued more GDD at a higher rate than in 2017 and the 2018 growing season length is within normal historical range for the region, fall frosts have continued to encroach into the growing season over the past two growing seasons (Figures 1 and 2). This year (2018), the lowest minimum temperature to-date on Old Mission Peninsula (26.0 F) and Leelanau Peninsula (30.2 F) was recorded on Oct. 18, while last year temperatures did not drop that low until Nov. 7 (Figures 1 and 2), according to Michigan State University Enviroweather.

These earlier and colder sub-freezing temperatures have led to widespread leaf fall and means 2018 has continued the trend with significantly shorter growing season (fewer consecutive frost free days) by roughly 10 days than in 2017. That difference is even greater when compared to 2016, resulting, again, in a relatively short or non-existent post-harvest foliated period. In fact, some grape producers have clusters on leafless vines which can have negative effects on the fruit and wood.

Figure 1. Minimum seasonal temperatures of Old Mission Peninsula from April 1 to Nov. 7 in 2016, 2017 and 2018. Source: MSU Enviroweather.

Figure 2. Minimum seasonal temperatures of Leelanau Peninsula from April 1 to Nov. 7 in 2016, 2017 and 2018. Source: MSU Enviroweather.

Introduction to frost damage in the vineyard

There are two main types of frost events according to Jorgensen et al., 1996: advection event, which is a horizontal movement of a cold air mass; and radiation event, which is a loss of heat into the atmosphere. Regardless of the cause, cool-climate viticulture is especially subject to frost damage at any time in the growing cycle (according to Gladstones, 1992), and previous research by Nemani et al., 2001, has determined the number of frosts per season can significantly impact wine quality.

Generally, frosts occur at the beginning (spring) and end (fall) of the growing season. According to Trought et al., 1999, spring frosts after bud development has started will decimate the potential crop tonnage for the season, while fall frost will directly damage the canes and maturing berries. Damage to maturing berries impacts fruit quality, and damage to canes and leaves leads to premature leaf fall and a lack of post-harvest assimilate storage (nitrogen, carbon, etc.) to support the following season’s spring growth, according to Shaulis and Pratt, 1965, and Trought et al., 1999.

Frost damage to grape berries

With low temperatures comes damage to the cells of the grape skin, a challenge that has been overcome in the past with careful and hasty harvest, and even adjusting the intended use of the grape with the production of ice wine. However, when low-temperature damage to the grape skin is followed by an increase in temperatures to the 55-60 F range, the susceptibility of the fruit to fungal infections, and in turn fruit deterioration, increases dramatically. This is something to monitor in the vineyard and may influence your harvest operations.

Post-harvest foliated period for overwintering vine components and post-harvest vineyard operations

Grapes still on the vine after the leaves fall (fall frost) by definition eliminate the post-harvest foliated period. The post-harvest foliated period is considered critical in cold acclimation and achieving maximum cold hardiness during mid-winter for vine components including the buds, canes, cordons and trunks. A long post-harvest foliated period is associated with increased nitrogen and carbon resource assimilation to the roots, which provide energy for early shoot growth the following season, according to Greven et al., 2016.

Since harvest season is winding down, it is a good time to refresh on post-harvest vineyard operations that may include assessing cold damage via assessing the bud and cane tissues for damage and the practice of hilling-up where soil is mounded to cover the base of the scion portion of the rootstock scion graft and insulate the base of the grapevine from damaging low winter temperatures. Information on grapevine cold hardiness, hilling up, assessing bud and cane tissue cold damage, and pruning strategies in response to cold damage can be found by clicking the links below.

• Winter injury resourceson the Michigan State University ExtensionGrapes website
• Grapevine Cold Hardiness: Mechanisms of Cold Acclimation, Mid-Winter Hardiness Maintenance, and Spring Deacclimation by G. Stanley Howell
• Assessing and Managing Grapevines in Response to Winter Injury by Thomas Zabadal
• Hilling-Up to Prevent Winter Injury in Vineyards by Rutgers University

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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