During the winter months temperatures here stay below zero and periods of below -20°C occur almost every winter. This has been the case for several years now, in early 2010 we endured almost four weeks of severe frost below -20°. This has not stopped me from growing tender perennials and plants that can endure only little frost over short periods such as lavender, roses and rhodohypoxis.
Lavender in spring just after snow is gone
I made some observations about the snow and the cold:
• This and the previous two winters we had significant snowfall before extended periods of frost set in and the snow cover remained (at least in my garden) until the worst was over. I did not loose a single of the tender plants that were covered by snow in the last two winters and my roses and lavender have been doing rather well.
• Snow has excellent insulating properties that keep warm and cold apart, even if the remaining snow blanket is only 5cm.
• Snow cover also protects plants from wind chill and being pulled by strong winter gales.
• I observed that when a snow blanket builds up on warm ground (above freezing that is) the ground below the snow remains unfrozen while covered, no matter what. Last spring I noticed tulips having grown 10cm into the snow when the snow from above finally was melting. Also the odd forgotten potato made it through winter in the vegetable patch, growing and croping last summer.
• In reversal, when ground was exposed to a severe freeze and then covered by snow, it took for ever for the snow to melt.
• Also, when snow was falling during very low temperatures, the cold got caught in the layer of snow and my neighbour measured still -15°C within the snow while outside temperatures where rising above +10°C.
Flowering lavender in July
Since making those obervations, I have been hoping for early snow in my garden and started to actively manage the snow cover to create extra protection of my less hardy plants: When digging my way through to the bird-feeders, I carefully shovel the snow onto the roses, my rock-garden and the lavender, increasing the chance that the snow cover will outlast the cold temperatures. Of course I also cover my roses with thick gardening fleece and some beddings with spruce twigs. Snow has the bad habit of pulling things down with it when it condenses, aggregates moisture and finally melts. The cover prevents twigs being broken off on the process.
Fleece or spruce twigs will also provide extra cover should the big freeze come before the snow. I doubt it will help for long though.
I also believe that snow protects plants from excessive wet conditions throughout the winter and turns into water for the plant just at the start of the growing season when the plants appreciate this most. Last two years I kept reading about hot and dry springs in England and Germany while outside the snow was melting.