Why do wineries bury their vines for winter?

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Not long after the last grapes have been picked in Prince Edward County, Ont., right around this time of year, workers are busy in the vineyards tucking the vines away for winter. They prune and gently lay down canes from tender chardonnay, pinot noir and other grape vines to be covered with a layer of soil that provides insulation against the sub-zero temperatures that are sure to come. The soil – and any layers of snow – will help keep vines safe and warm.

A similar scene plays out in vineyards in Quebec, China and other wine-growing regions where winter temperatures dip below -24 C. Vinifera vines are killed by prolonged exposure to temperatures of -25 C. Depending on dormancy, damage to the buds that become the next crop of grapes happens around -15 C. Managing your vineyard through these brutal conditions is key to its survival.

Warmer temperatures in other Canadian wine regions saves growers from such drastic measures. In late fall, most go through their vineyards and gather soil around the base of the vine, “hilling-up” to protect the grafted grapevines. That way there’s an opportunity to retrain the vine should the exposed canes suffer damage from winter’s blast. Wind machines also dot numerous vineyards throughout Ontario to help mitigate more vicious cold spells. These giant fans help to increase temperatures around the vines, but only work on relatively calm days or nights without much wind.

In the County, burying vines or using a geothermal blanketing system is a crucial measure against conditions that can damage the delicate buds on the vines, resulting in a reduced crop for the next year’s harvest, or worse. Damage to the trunk of the vine, which increases the risk of disease or infection, or its demise leaves growers facing years of lost income or the necessity of replanting before the next viable crop.

At this point, many wineries in the County have finished or are in the process of getting their vineyards ready for the cold nights and days to come. COVID-19 restrictions and a shortage of workers have slowed the process for some. Even with the variety of imaginative devices that have been designed to attach to tractors and help with the labour-intensive process, the practice requires time and effort to do properly.

Growers might have streamlined the burial process over years of repetition, but there’s no easy answer when it comes to deciding when to unearth the vines. Too early in spring and you risk suffering the effects of frost. Too late and you risk bud rot from soggy soils or damage as they’re dug out. For these intrepid wine makers, the health of their vineyards is an unrelenting, year-round concern.

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