Air temperatures over winter receive much of the attention for affecting the winter survival of lavender in Ontario. This is for good reason since bitterly cold temperatures have been known to wipe out entire crops of lavender. Row covers have proven to be very effective at reducing these risks. This winter, air temperatures up to this point have not been a real concern since the coldest temperatures recorded were around -22°C on calm nights. It also helps that many areas had deep snow cover covering plants at the time.
The other factor that can kill lavender plants over winter is meltwater combined with frozen ground and thaw and freeze cycles that trap that water on the surface around plants. This poses far more danger for plants this year considering the incredibly deep snowpack in many areas, especially in the snow belts. Lavender does not like wet feet, not because the water itself is damaging, but because the water prevents oxygen from getting down to the roots. Without adequate aeration, the roots start to die, and then can be finished off by pathogens in the soil later in the spring. Ice can be equally as damaging for the same reason. Respiration of plant parts is much slower in the winter, so the plants can withstand short periods of standing water.
The problem with meltwater is that the soil texture is irrelevant. With frozen ground, it doesn’t matter how sandy the soil is, the water cannot infiltrate the soil. Surface runoff is the only way to get rid of the water. The deep snowpack can prevent the flow of meltwater during warm periods, only for the water to freeze solid when temperatures go back below freezing.
What Can You Do?
During warm days, get out into the fields with your rubber boots and find standing water. Cut channels through the snow and/or soil for that water to run out of the field before it has a chance to re-freeze.
These conditions highlight the importance of planting lavender on a slope to allow for more rapid drainage at all times of the year. If planting on flat ground in the future, consider how you can improve drainage from the site with channels or broad raised beds.
