By Sean Westerveld, Ginseng and Medicinal Herbs Specialist
University of Guelph, Ontario
The most important factor to consider when choosing a lavender variety in Ontario is winter survival. It does not matter if a particular variety has all the best visual and oil characteristics if it doesn’t survive the winter.
Winter survival assessments have now been completed for two years on most varieties in the provincial lavender variety trials at six sites in southern Ontario. The winter of 2010/11 was cold with steady temperatures and snow cover, while the winter of 2011/12 was mild with variable temperatures and virtually no snow cover. Consequently, winter survival was variable between the two years, especially among sites. Winter survival was rated on a scale of 0 to 10 with 0 being completely killed and 10 being 91-100% healthy.
While the overall average winter survival ratings across all six sites and all varieties were relatively constant between 2011 and 2012, the relative ranking of the varieties and the sites was very different between the two years. Lavandula angustifolia varieties (angustifolias) survived the winter of 2010/2011 much better than Lavandula x intermedia varieties (lavandins). However, in 2011/2012 lavandins survived better than the angustifolias. Despite major differences in weather conditions between the two years, ‘Folgate’ had the highest winter survival rating of the varieties in both years, and ‘Fat Spike Grosso’ had the highest winter survival rating of the lavandins in both years. The only other varieties to have a rating greater than 7 in both years were ‘Royal Velvet’ and ‘Edelweiss’. The varieties ‘Alba’, ‘Provence’, ‘Premier’, and ‘Tuscan Blue’ had very poor performance in both years and are not recommended for production in Ontario without winter protection. ‘Sharon Roberts’, ‘Fred Boutin’ and ‘Twickle Purple’ have only been tested for one year, but also showed poor winter survival across all sites.
In 2010/2011, winter survival was lowest at Farm A in Essex County, which is the warmest site. In 2011/2012, the same site had the highest winter survival rating. Farm E located in Elgin County had very poor winter survival. The results may be related to the warm period in March, which was followed by a deep freeze. Plants may have begun to break dormancy and then were damaged by the freeze conditions. This could also be true on Farms C and D in Norfolk County. These three sites are located in areas more prone to spring frosts than the other three sites. Farm B in an area of Norfolk County less prone to frosts and Farm F in York Region had fair to good winter survival in both years. Most of the damage in 2012 consists of weak or dead branches, with new growth emerging from the base of the plant. Freezing conditions this spring may have damaged the existing plant material, resulting in sprouting of the dormant buds along the lower stems. Few plants in the trials are completely dead, which suggests that plants will recover, but with the loss of one year’s worth of growth.
The results suggest that variety performance in Ontario is very dependent on growing conditions on a specific farm and on weather conditions over the winter and early spring. Growers should test different lavender varieties under their own growing conditions before expanding to a larger acreage. Although results are still preliminary, ‘Folgate’, ‘Royal Velvet’, ‘Fat Spike Grosso’, ‘Edelweiss’ appear to consistently survive the winter in Ontario and have a better chance of success under different weather conditions. Trials will be initiated in 2012 to test different row covers for winter protection of less hardy varieties.