Drought takes toll on valley’s trees, expert says

TWIN FALLS, Idaho – Imagine a landscape without anything to shade you from a sun that can send temperatures above 90 degrees for months on end. Now, remove anything that might block the endless, hot, dry wind.

If you think you’re on Mars, think again. This fictitious terrain offers a glimpse of what the Magic Valley looked like before irrigation, before trees.

Truth may be stranger than fiction unless residents tend to existing trees stressed because of drought that has plagued the area for nearly six years, said Dave Kiesig, horticulture instructor at the College of Southern Idaho and certified arborist.

“These trees are speaking to us – very loudly,” Kiesig said recently while on a stroll around the CSI campus.

“Trees move in super slow motion,” he said. “When they get sick or die, they’ve been suffering for at least a year before they show symptoms. Even a newly planted tree can take up to two years to die.”

If a tree can take up to two years to die, how can its caregiver spot signs of stress before it’s too late?

As he walked from the Evergreen Building at CSI toward the Eldon Evans Expo Center, Kiesig noted how drought affects different trees in unique ways. He pointed to several bare branches on a Norway maple, to heavily coned branches of Colorado spruce and to discolored leaves of a Catalpa. In its own way, each tree told a story – the same story of suffering.

“Trees are like people – they all have their own personalities,” Kiesig said. “Trees, like people, have different needs.”

Besides obvious signs of leaf and needle loss, drought-stricken trees produce more fruit and seeds. The lack of sufficient water triggers a survival mechanism in trees, Kiesig said, propelling them to reproduce. Trees infected with insects could also be suffering from a lack of water. “Insects and pathogens will not bother healthy trees,” Kiesig said. “Those are symptoms of a larger problem.”

The stress of inadequate water on trees makes them more susceptible to insect and pathogen infestations, Kiesig said. These trees require extra care – not only to rid the plant of insects, but also to restore its defense mechanisms by ensuring the tree receives sufficient water.

“It’s a long process,” Kiesig said. “There’s no quick fix.”

Kiesig recommended several steps to tree health: deep watering trees, aerating and either composting or fertilizing lawns.

“The root system is the most important part of the tree,” Kiesig said. “Ninety percent of trees’ roots are found in the top two inches of soil.”

The feeder roots of a tree are the thinner, almost hair-like, roots located relatively close to the surface. Feeder roots absorb water and nutrients. These roots spread out across an amazingly wide area.

For example, if a tree’s crown has a diameter of one foot, its feeder roots fan out four to five feet in every direction. If you live in town, Kiesig said, your tree’s roots often aren’t even in your own yard. A neighbor installing a new driveway or sidewalk could affect a tree in your yard, he said.

Because feeder roots grow at a depth below that of grass roots, deep watering is essential to reach those roots.

What is deep watering? Put down the shovels, and turn on those soakers.

“You water until the ground won’t hold any more, until you get runoff,” Kiesig said. “Do it slowly. Let it trickle for eight to 24 hours. The water has to run off. It has to move. At that point, the soil is saturated.”

However, Kiesig warned, it is possible to drown plants. Trees, like humans, require oxygen and take it from the soil. “That’s why we only do it once in awhile instead of on a regular basis,” he said.

In addition to deep watering, people should try to have their lawns aerated in the spring and fall. After aerating the soil, residents should consider either using a compost or fertilizer. Compost actually restores organic matter to the soil and is less expensive, Kiesig said.

Tree fertilizers normally include nitrogen, phosphorus and potassium as well as micro-nutrients. Pay attention to the amounts of sulfur, as well, Kiesig said. “It’s hard to give plants too much sulfur,” he said.

Sulfur breaks up some nutrients in the soil and enables feeder roots to absorb those nutrients. Aerating opens the ground up for faster and easier absorption of fertilizers or composts.

The loss of a large tree affects much more than a yard’s aesthetics, Kiesig said. Tree shade can lower temperatures by 15 degrees. Certain types of turf don’t fare well in direct sun. Other plants growing in the yard may also be harmed by depleted shade. The homeowner may need to increase not only the frequency but also the volume of watering.

“If trees are lost, the impact is going to be huge,” Kiesig said. “Even though they’re a renewable resource, I preach that they’re the most important organism on the planet.”