Winter drought damage not a reason to panic
We have a river birch that I planted about 15 years ago on the property line between my neighbor to our east and us. It is a clump style with three main trunks. This year the side that faces my yard (the west side) is not doing as well. The leaves are smaller and some have brown edges. The portion facing east seems to be well, with full, darker green leaves. Is there something I can do?
I think the problems you’re seeing are due to winter drought damage. Birch do OK here; they’re plenty cold-hardy for us, but it’s our dry desert climate that can give them problems. People see winter drought damage in the spring when a portion of the tree (usually towards the top) fails to leaf out or leafs out sparsely with small, scattered leaves like what you’re seeing on your tree.
Birch are totally intolerant of drought, and believe it or not drought can hurt a plant just as much in January as it can in July. I tell people to plan on watering the tree about once a month throughout the winter, modifying that schedule depending on what the weather is doing. If it’s warmer and drier than normal, you should water more often, but if we’re cold and getting good moisture, then you can take a little break.
It’s also important to remember that this schedule begins when you stop watering in late October. Sometimes people think that “winter watering” means January and February, but November and December can be our warmest and driest months during this time, so start the clock when you stop watering in the fall and hold to it until you get ditch water and are ready to start regular watering in the spring.
Before you start feeling bad about “failing” your tree, I had a beautiful clump of paper birch in my front yard almost 20 years old. About 10 or 15 years ago I got complacent one winter and assumed that I didn’t need to water and I hurt the tree. I knew better. I preach this sermon over and over and still did it. Once the tree was drought stressed, bronze birch borers moved in, which attack trees in that condition. After fighting those little monsters for three or four years, we had to remove it. The key is to keep the tree as happy and healthy as you can make it and that starts with watering.
This past winter, I think the problems with drought occurred from late February into April. We were 10 to 20 degrees above average and well below average on precipitation. I’m seeing plant samples this spring from a number of different plants that were drought-injured.
There are three things to do now that you have this situation. First, don’t overreact. The tree may have been hurt by drought three or four months ago, but overwatering now won’t change that. Keep up your normal watering schedule right now — it’s worked for your tree for 15 years. Be sure to water the tree deeply but allow the soil to dry out just a bit before soaking it again.
The second thing to do is to proactively treat your tree against borer. Fortunately, we now have better insecticides available to the homeowner to deal with bronze birch borer. Imidacloprid and dinotefuran both do a great job on them. I prefer dinotefuran since it gets into the tree faster and doesn’t last as long as imidacloprid but it can be hard to find. Either one is applied around the base of the tree and watered in so it’s easy to treat a larger tree. I’d do it right now and plan on applying it in late March or early April for the next two or three springs.
Lastly, don’t forget about having to water during the winter. There’s a group of three trees we tell people they have to stay vigilant about winter watering for as long as they have the tree. Birch is one; the other two are Colorado spruce and redbud. Of course, situations will vary from yard to yard and even from place to place within the yard. Some people have a susceptible tree and they’ve never winter watered, but I think they’re more the exception than the rule. Winter watering is a good thing to plan on doing if you have a susceptible plant or if it’s the first winter for the plant in your yard.