Don't you just have to shake your head in disgust. After enduring a long prairie winter and looking forward to getting back out in the yard to do some gardening, spring slowly warms up and you notice that your cedars, young spruce or other evergreens are getting browner, not greener.
They are victims of winter desiccation or winter burn. They dried out. But how?
Water gets into plants from the soil when the soil is moist. The wind and the sun draw moisture out of the tree or shrub (transpiration) and cause a negative concentration of moisture in the plant. When the water concentration is negative it allows for the passage of moisture from the soil (higher concentration of moisture) into the plant (lower concentration of moisture). See? Water can flow up hill. But because we live in an area where there are eight months of winter and four months of tough sledding', if the soil is frozen, the water can't flow into the plant. Ice cannot move from region of higher concentration into a region of lower concentration. If the water can't be replaced, the tree or shrub begins to desiccate or dry out.
Sometimes its just a little discolouration of the needles or evergreen leaves, but it can be death of the plant as well.
Damage will always be worse on the side exposed to the wind or sun, especially close to a building where the winter sun causes the building wall to warm up. And damage will always be worse on newly planted trees and shrubs due to the lack of root development in the year of planting. No roots, no water.
How do you guard against winter desiccation?
Water.
When do you apply this water? Right now. As soon as the leaves begin to colour up and fall to the ground, take this as your cue to start watering in your evergreens for winter, before freeze up.
Mulching with bark chips or other mulch material helps protect the soil from drying out as well.
For more sensitive evergreens (like cedar) in an exposed planting site, sometimes a barrier is required to protect the leaves from wind and sun exposure. The material should be breathable, like burlap, and it is always better that the burlap does not contact the leaves. Put three stakes in the ground around the shrub you want to protect and build your burlap wall attached to the stakes, not the shrub.
As soon as the soil thaws and we move into the tough sledding' part of the year, water all your evergreens first.
- Certified arborist since 1988, Keith Anderson is the executive director of the Prairie Chapter of the International Society of Arborculture.
