Pine Tree

A pine in your mix of trees is going to thrive on summertime neglect and suffer potential root rot when watered as you would some other trees.

Tim Smith, WSU Master Gardener

Tim Smith

WSU Master Gardener

Keeping a lawn, trees and garden green and growing in a rain-shadow desert isn’t always easy. If you live in central Washington, and I assume most of you do, maintaining your lawn, ornamental flowers, shrubs and trees is a delicate balance and difficult, and a bit of an art.

An avid gardener often finds the way. Most of us muddle along, irrigating the lawn when it starts to look dry. Many trees don’t respond well to the way we water the lawn that may surround them.

Look at the valleys, hills and mountains around here. Lawn grass is adapted to places like Kentucky, where it is wet all seasons, and we need to mimic that weather by irrigating in order to keep it growing through the hot, dry weather. This frequent irrigation is not what some trees need.

Trees need irrigation to grow at their best, but some prefer periodic drought, as long as they have some supplemental water in the spring and late fall.

What do you see growing naturally as the lowest elevation native tree species? Pines, mostly Ponderosa, or sometimes Lodgepole. These trees need just a little more yearly water than the grass and shrubs that dominate lower, dryer sites. Pines do well at lower elevations if watered in the fall and spring but left dry during the heat of summer.

A pine in your mix of trees is going to thrive on summertime neglect and suffer potential root rot when watered as you would for aspen, birches, willows or poplars. All these species will stand up well, sometimes too well, because they are adapted to wet summer conditions. These trees are often found near open water and commonly grow with their roots immersed in running water. Not so for pines.

If you look around in the woods, you often see pines clinging to life while rooted in the crevice of a rocky hillside, a testament to their toughness. And yet we plant them in our yards next to blue spruce, or sub-alpine fir. We end up with species adapted to three radically different climatic conditions, none of them similar to ours.

Evergreen trees are often brought to the WSU Master Gardener clinic for diagnosis of problems. These problems may result following years of decline, culminating in the eventual poor condition or death of the tree.

There is rarely a cure for the trees in trouble. The current symptoms on the tree may be the result of some problem in the distant past. Root-rot organisms that do not attack the tree while the soil is warm and dry may overwhelm the defenses when the soil is warm and wet. Pines also resent covering of roots by fill or cutting of their roots by nearby construction. Root problems lead to a weaker tree that gets targeted by bark-boring beetles which determine which trees to attack by sensing that the weak tree is slightly warmer than the healthy trees near-by.

Is the culprit the bark beetles or the original cause of the trees’ weakness? Can you stop the bark beetles by spraying? No, that’s impractical.

Evergreens are not unique in their sensitivity to natural growing condition. It helps if you organize your yard and manipulate irrigation to best match water needs.

Note: Another plant that doesn’t like to be over-watered is the watermelon. This plant is native to the deserts of southern Africa and grows best-quality melons if watered infrequently.

A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Tim Smith is one of four columnists featured.