Thursday, February 28, 2013

Snowblind Trees?

The shadows are still relatively long but the days are getting noticeably longer,  .... and warmer. Day by day, as the sun creeps its way higher into the sky, we gardeners, especially those of us that live in the North, start to get a little anxious for the coming growing season. The winter world in the North can get to be a bit long in the tooth come late February. There is a whole new world lying just beneath the snow and we know it. The urges to get that shovel into the ground start to become stronger.  Placing and receiving seed, plant, and supply orders only seem to make the waiting worse.  Patience. ... It won't be long before we start seeds and from then on we won't even have time to breathe. We anticipate the transformation every year at this time.

Not so fast! We have other issues to worry about right now.
Recently, we have had some very bright and warm days here and for most, it is very welcomed. Not so for trees. This is one of the most stressful times of the year for trees, especially conifers. The combination of strong sunlight compounded by reflection off the snow and warm temps can spell disaster for conifers.

This Limber pine (Pinus flexilis 'Vanderwolf's Pyramid') is beginning to show signs of dessication injury indicated by the browning needles.
The problem is dessication injury. In fact, most winter damage in landscape conifers is exactly that.  The concept is that when it is bright and warm, the tree starts to transpire. This means that the tree is releasing water vapor into the air.  At least it tries to. The problem is that the roots can't supply the demanded moisture because they are embedded in frozen ground  Think of it as trying to sip on a straw that is in a glass of frozen water.  The leaves (needles) simply dry out. This is the damage that you see.  Deciduous trees are not as affected by this because they don't have leaves this time of year.  After all, it is the leaves that conduct the moisture. Mature conifers and those that are well adapted to the area seem to be much less affected. Landscape and marginally hardy conifers are particularly susceptible.
There is some Rx for this. Shading the tree from the bright sunlight is often beneficial. The light is the catalyst for the whole process of dessication. The thinking is that if you can eliminate the sunlight, you can eliminate the demand for moisture, thereby eliminating the injury. It may be a little unsightly but it beats the alternative. It is another one of those spring rituals that we reluctantly go through here at the garden, especially when there is snow cover.

Although snowblindness is a human affliction, the reflective UV rays are pretty hard on trees too. If you have ever experienced snowblindness or gotten a sunburn from the snow, you know how dangerous sunlight off of snow can be. Trees don't have the luxury of coming in out of those conditions. They have no sunscreen nor do they wear sunglasses.

Around here, landscape care is an ongoing and year-round endeavor.

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