Winter Injury

People have remarkably short memories, particularly in regards to the weather. While Boise and most of the West have enjoyed late spring-like temperatures since early February, we've watched (gloating a bit at times), as the east has been pummeled by an unrelenting winter.

I've heard folks describe our winter as one of the mildest they've ever seen in our area. So why do so many conifers that looked so peachy back in the fall now look this?

Or like this?

A recent post by a respected local garden blogger described it as the result of bitter cold we experienced earlier this winter. Cold? Yep. It got cold (1 F°), but only briefly and well within historical averages and certainly within the tolerance of the many conifers that were damaged this winter.

So what gives?

The short answer is it's not the cold per se, but rather the whiplash nature of the weather in November. We enjoyed a late gardening season with warm weather into November, and then we were nailed by a polar vortex that dropped temperatures from a high/low of 69 F°/46 F° on November 9th, to a high/low of 22 F°/1.2 F° less than a week later!

Some plants just have a really tough time riding these kinds of rapid transitions. One of the conifers that has struggled the most in Boise is the Hinoki cypress. I bet you can pick it out in this line up.

Here's another Hinoki cypress in my own yard.

And another Hinoki cypress in my parent's landscape. Note how green the bamboo looks (what winter?).

Another interesting aspect of this "whiplash weather" is how it impacted the same kind of tree so differently. A friend and I were puzzling this morning on why the White pine on the left fared so poorly compared to his buddy on the right. Southwest exposure? Wind protection/exposure? A difference in the water holding capacity of the beds on either side of the driveway? Go on, speak up if you think you know.

Unsurprisingly, I've had numerous calls and consultation requests during the last month. My advice? First, given our warm weather, seriously consider turning on your sprinklers early this year. Desiccation is really rough on a weakened tree. Second: be patient and wait to see if the tree pushes new growth. It may be June until you can really see the extent of the permanent damage. My prediction is that most of the pines will spring back. I'm not so sure about some of the Hinoki cypress (including my own).