Dying Douglas Firs

August 9th, 2016

You’re not imagining it if seems like your Douglas fir trees are getting thinner and thinner. And you’re not alone either.

This is my Douglas fir, in the process of dying from Swiss needlecast.

This popular species of screening evergreen is running into increasing disease trouble lately, leading to widespread drop of needles and the bare look that accompanies the loss.

A pair of fungal diseases called rhabdocline and Swiss needlecast are thinning Douglas firs mercilessly all over central Pennsylvania and killing some of them after years of infection.

We had a bigger-than-usual August needle drop due to a dry summer last year, but if your trees didn’t improve noticeably this spring, odds are you’re dealing with needlecast.

I wrote a detailed piece on this problem for PennLive last December, but the bottom line is that if you have needlecast, you’re either looking at spraying fungicides three to four times each spring or watching your Douglas firs get barer and barer each year from the bottom up.

I’m seeing that happen now to the Douglas fir that our kids brought home as a little whip from school more than 20 years ago. It’s about 35 feet tall now and had been doing well until about 3 or 4 years ago.

Now, it’s looking bare and sickly for the first 20 feet – including dead limbs up to about 6 feet. I’m not going to spray.

When limbs drop needles and die, about all you can do is prune them off. You can tell they’re dead if you scratch off a little bark and notice brown or gray tissue inside instead of green. Dead wood also snaps instead of bends.

The problem with pruning off lower limbs is that leads to a very difficult planting place. Not a lot of plants will do well or even survive in the dry shade and root competition underneath a limbed-up evergreen.

Even tougher is when the tree is in a sunny area, allowing direct rays to penetrate the ground underneath the raised limb structure. That’s now dry sun along with root competition – kind of the equivalent of Death Valley to plants.

In my recently bared area under Dying Doug, I’ve already ringed the west-facing side with a planting of creeping sedum ‘Angelina’ – a heat-, sun- and drought-tough succulent that has golden foliage and yellow flowers in June.

I’ve also planted some sun-tolerant coleus there. Some of the newer coleus are surprisingly durable in back-yard-desert conditions.

And I’ve moved a young viburnum to the back side of the limbed-up area, where I’m hoping it’ll tag-team with the remaining fir branches to give me screening for at least a few more years.

In the fall, I plan to move a Glow Girl spirea to the bed and fill in behind it with some lime-green hosta I have elsewhere. Thicker-leafed hostas like these not only are pretty good in the dryness around tree roots, but they also tolerate sunnier spots better than the thin-leafed, variegated-edge hostas that are the most common.

This game plan should work, although I’ll have to carefully watch the water there for the next year. Any young or newly moved plant – including drought-tough ones – need to have consistently moist soil until their roots can adequately reach out.

Cherry laurel is a broad-leaf shrub that I’ve seen do reasonably well around roots in sun or shade, if you’re looking for other ideas.

Liriope – the grassy-like perennial that blooms purple in late summer – is one of the best perennials for roots in sun or shade.

And if you don’t run into the new blight disease floating around, boxwoods are another shrubby evergreen choice for under limbed-up trees.

Good luck if you have Douglas firs. You might want to take a closer look. And if you’re thinking about adding new evergreens to the landscape, I’d suggest something like Oriental spruce, Bosnian pine, Green Giant arborvitae or cryptomeria ‘Yoshino’ or ‘Kityama’ instead.