Caring For Your Trees In Winter

Why does my evergreen look so weird? To prune or not to prune? Mulch? Which trees are the best for Seattle? When can I plant? We asked certified arborist Rick Castro of Davey Tree, who has been caring for trees for over 40 years, to help us out on these questions and more. Read on.

Trees are the stars of the winter landscape, but winter holds special challenges for them – they have to endure everything from bouncing between spring-like afternoons to freezing nights, to rounds of floods and windstorms. So how can we keep them thriving?

Lack of water, even in our infamous rainy season, is a critical concern, says Rick. So although you may be soaking wet, your trees could be literally dying of thirst.

Many Seattle gardens are built on a layer of glacial till, that hardpan layer of “soil” that makes your shovel clang when you hit it. The till is so hard, it sheds water away like granite. Freezing, when it happens, makes the topsoil do the same.

So, the optimal plan would be to water your trees heavily in late summer and fall before the rains hit, and then mulch them to hold in that moisture in reserve. Don’t worry if you missed that memo – there’s still time to mulch.

Rick recommends laying an organic mulch no more than two inches deep, as wide as your budget allows. “Many people will do a two-foot circle, which is OK, but if you can go all the way to the drip line of the tree, all the better.” The drip line on the ground mirrors the reach of the tree’s outer branches. Make sure to keep the flare of the root crown (at the base of the trunk) open.

People often wonder about their evergreens at this time of year. Some take on bruised purple tones, some turn brown from the inside out, some from the outside in.

Those first two are likely natural, says Rick. Frosty temps can bring out unusual coloration in many evergreens, from Rhododendrons to False Cypress (Chamaecyparis). Browning on the inside is perfectly normal for Cedar species; it’s just an annual shedding of older needles. However, if your evergreen is turning brown from the outer needle tips in large sections, as here, call an arborist to check it out.

As to pruning, for evergreens, especially firs, Rick thinks less is more. Keep to pruning crossed or weak branches, or those extending beyond the root zone. Winter is, however, a great time to prune dormant deciduous trees, including fruit trees – you can see what you’re doing, and there is less biomass to haul. Dead branches on any tree, such as after a wind-storm, should be removed promptly.

If you’ve had a wind-storm, and you’re concerned your tree may be ready to fall, here are some warning signs to look for:

– the tip of the tree (not the trunk) is suddenly leaning

– there is loose ground at the base of the tree where the trunk meets the ground – as if it’s been shaken loose.

And if the ground isn’t frozen, you can plant new containerized or bare-root trees now.

Some of Rick’s favorites for Seattle are classics and natives: Douglas Firs (who he says love our wet winter/dry summer combo – but don’t plant them in an irrigated lawn), Bigleaf Maples, Red Oaks, and Western Red Cedars. For smaller trees, he recommends Styrax, Stewartia, Paperleaf Birch and Japanese Maples.