Hedging and Canopy Management in Grapes

By Spencer Leidl (Summer Student) and Kathryn Carter (OMAFRA)

In two of our recent articles, we touched upon early season canopy management in vineyards. Canopy management continues throughout the year, and there are many different techniques that can be used to manage growth. In this article, we will talk more about the hedging technique, why it is used, and its benefits and challenges.

What is Hedging?

Excessively vigorous vines tend to outgrow their trellis system, resulting in shoots growing up and over the top catch wires and dropping down over the sides of the vine, causing shading. Hedging is a technique used to remove excess primary and lateral shoot growth from the top of the vine and sometimes sides of the canopy (Goldammer, 2018).

Grapevines need only 15 leaves per shoot to fully mature the crop. Excess leaves above and beyond this number only divert resources from the ripening fruit. Hedging vines a foot or so above the top wire and the sides of the vine (if necessary) can create a better balance between vegetative growth and crop, while eliminating unnecessary shading. During hedging, about 10-20 percent of the canopy is removed to assist in shade and vigour reduction and to increase air flow, resulting in improved fruit size, quality and a reduction in diseases (Olmstead, Williams, & Keller, 2006). By removing young leaves at the top and sides of the canopy, a grower can cause a carbohydrate “sink”, slowing development. Hedging is a versatile tool that can be used at various times throughout the development of a vineyard, as well as throughout the growing season to provide an adequate microclimate for developing fruits. In Ontario, most hedging is done with machinery, using tractors with hedging attachments. 

Why is Hedging Used in Vineyards? What are some of the Benefits of Hedging?

Hedging is often used in developing vineyards, as it allows for a more uniform vine to be established, with a similar number of buds across the vine.

Hedging has a multitude of benefits for growers, including (Goldammer, 2018):

• Prevention of shading for fruit
• Cessation of shoot entanglement between vine rows resulting in more manageable vines
• Allows for ease of traffic, both workers and mechanical, throughout the vineyard
• Generates uniform shoots in young vineyards

Hedging can also assist in creating higher quality fruit for the grower. In a 2013 study by Kok and associates, hedging 15 leaves on each shoot when the berries were pea-sized (7 mm in diameter) gave the berries a longer length and greater weight than the control vines. The resulting fruit also had lower titratable acidity and a higher anthocyanin content than the control (Kok, Bal, & Celik, 2013).

What are Some Challenges?

The timing of hedging may be a challenge, as hedging at different times will produce different results. Hedging is usually completed between fruit set and veraison, but if it is done too early in the season (before fruit set) it may influence lateral growth, which can increase the canopy density (Goldammer, 2018). As well, early hedging when the soil is very moist can promote lateral shoot growth, leading to an increase in canopy density (Grant, 2000).

Severe hedging, or hedging late in the season, can take away too many leaves, which can reduce photosynthesis, node hardiness, and anthocyanins, resulting in delayed- fruit ripening (Reynolds & Wardle, 2000, & Grant, 2000). As a general rule, avoid hedging canopies more than 2 or 3 times each season. Hedging is a short-term (band-aid) solution to managing vine growth, and the need for frequent hedging is an indication that the vines are not in balance and there may be other issues (i.e. excessive fertilization, poor vineyard site selection, or inappropriate training systems) that should be addressed. Growers should investigate their practices if they are having to hedge often. Hedging itself increases shoot growth, resulting in wanted lateral growth, and the need for even more hedging.

Timing for Hedging

Shoot hedging should be done after fruit set when the shoots start drooping over the catch wires, but before veraison, as this will allow the vine to develop new leaves, which will produce sugars to support the fruit. The benefit of early season hedging (after fruit set) is that it results in a younger canopy that is more efficient with photosynthesis. Delaying hedging until later in the season results in an older canopy that is less efficient (Sabbantini, 2020). Late season hedging (after veraison) will direct the vines energy to a new flush of lateral growth, rather than the fruit, which may result in delayed fruit maturity and a reduction of wood maturity and winter hardiness (Cartechini et al., 2000). In most vineyards, hedgers are used to reduce the amount of labour required for hedging (Figure One). Dr. Justine Vanden Heuvel (Cornell) has been investigating the potential use of palissage training as an alternative to hedging. Palissage involves wrapping shoots along the top catch wires in a VSP system or tucking the shoots down into the interior of the trellis to reduce vigourous growth (Vander Heuvel, 2018).

Conclusion

Hedging is a useful tool for managing vine vigour, reducing shading, and providing a more evenly spaced, uniform canopy with good air flow. The timing for implementing hedging can have different impacts on the vine. Labour costs should also be considered by the grower before any canopy management technique is decided upon.

Reference

Goldammer,T. (2018, March). Vineyard canopy management. In Grape grower’s handbook. Apex Publishers.

Grant, G. (2000, July). To hedge or not to hedge? Lodi Wine Growers Commission. https://www.lodigrowers.com/to-hedge-or-not-to-hedge/

Kok, D., Bal, E. & Celik, S. (2013). Influences of various canopy management techniques on wine grape quality of V.vinifera L. cv. Kalecik Karasi, Bulgarian Journal of Agricultural Science 19(6). 1247-1252. Retrieved from http://www.agrojournal.org/19/06-12.pdf

Minnesota Grape Growers Association. (2015). Care of established vineyards canopy management. Minnesota Grape Growers Association. https://cdn.ymaws.com/www.mngrapes.org/resource/resmgr/Growing_Grapes_in_MN_Best_Practices/Chapters/Ch_8_Canopy_Management_2015.pdf

Olmstead, M., Williams, K., & Keller, M. (2006, December). Canopy management for pacific northwest vineyards. Washington State University Extension. pubs.cahnrs.wsu.edu/publications/pubs/eb2018e/?p-page=7

Reynolds, A. & Wardle, D.A. (1989, January). Impact of several canopy management practices on growth, yeild, fruit composition, and wine quality or Gewurztraminer. American journal of enology and viticulture. 40. 121-129

Sabbantini, P. (2020, June 4). Canopy management approaches between bloom and fruit set. Michigan State University. https://mediaspace.msu.edu/media/Canopy+management+approaches+between+bloom+and+fruit+set/1_3qgkrw4t/167253541

Vanden Heuvel., J., France, J. & Chou, M. (2018). Palissage reduces cluster zone lateral shoots compared to hedging. Cornell College of Agriculture and Life Science. https://grapesandwine.cals.cornell.edu/newsletters/appellation-cornell/2018-newsletters/issue-35-november-2018/research-plain-english/