Marianne Ophardt

Trees' decline may be from inadequate watering

Kennewick, Wash. -- Wow! After such a cool spring, this hot weather has come as a shock to us and our plants.

A number of local residents have been dismayed to find their landscape trees suddenly dying. It's likely that many of these trees showed signs of decline in the past, but the stress from the sudden onset of summer has been a tipping point.

There are two main categories of trees biting the dust: newly planted trees in the ground for less than three years and trees in place for longer.

Today, let's talk about the young or newly planted trees. In the past, I've talked at length about the correct way to plant trees. Rather than repeat myself, you can obtain a free copy of a Washington State University Extension publication "FS047E Planting Trees and Shrubs in the Landscape " at

Let's discuss how to investigate why young trees are dying. First, check the root system to find if it has grown out of the original root ball. According to tree expert Dr. Gary Watson of the Morton Arboretum, "under favorable conditions, roots can be expected to grow approximately 18 inches per year."

So if you planted a tree correctly last spring, this year you should be able to find roots growing at least a foot or more away from the original root ball, even more if it's been in the ground longer. Carefully dig down to find if the roots have indeed grown out. Use a trowel and a hose to carefully excavate, starting at the perimeter of the original root ball.

How are the young trees being watered? Many conscientious gardeners wanting to conserve water have shifted their trees and shrubs, particularly those in landscape beds, to drip irrigation. When a new tree or shrub is planted, the drip is often positioned at the base of the plant. This may seem logical, but depending on the type of soil and the emitter used, the water may be simply pooling at the base of the tree and not moistening the entire root ball and the area beyond. This results in a poorly developed root system and a drought stressed plant.

Again, use a trowel to check the moisture in the root ball and in the soil just beyond where the roots are growing. It's crucial to have roots growing into the surrounding soil as the top of the tree grows bigger. Those roots are responsible for absorbing water and nutrients to support tree growth. If that doesn't happen, the tree can't grow into a healthy older tree.

Don't place drip emitters right at the base of a young plant, position them several inches or more away from the trunk. Keep in mind that as the tree roots grow outwards the moisture needs to be applied in the area of the outward edge of the roots and just beyond. That's where the fine roots that take up the water and nutrients are located, not at the trunk. You should adjust your system to be moistening the soil to a depth of 18 to 24 inches in the root zone, not at the base of the trunk. This may require using more emitters, sprinkler-type emitters or a soaker hose.

For young trees in lawn areas, don't rely on lawn sprinklers to provide adequate moisture. It's likely you will need to apply additional water to newly planted trees using a soaker hose or individual sprinkler, especially during the first several years after planting.

* Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.