“How many must die?”
This was the subject of a recent e-mail message from Cass Turnbull, founder and leader of Plant Amnesty – an organization devoted to educating the public on proper care of our landscapes.
It reminded us that the lack of water will kill some of our beloved plants, shrubs and trees. The recent record-setting temperatures and the dry summer has caused some to die while others are approaching critical condition.
The following information will help homeowners decide whether or not to water their landscapes.
How deep do roots grow?
Generally root systems are quite shallow. It depends upon the soil conditions, size of plant and species.
Roots usually grow within the top 18 to 24 inches of the soil. Most of the uptake of moisture and nutrients occurs in the tiny root hairs at the outer edges of a root system. These small roots are often in the upper 12 inches of the soil while the larger anchoring roots closer to the trunk may grow to depths of a few feet.
How far out do root systems grow?
Generally conifer trees that have needles develop root systems that may extend to or slightly beyond the “drip line” or the outer edge of a tree’s crown.
Deciduous trees may have root systems that extend several feet beyond a tree’s drip line. Consequently, a root system can spread dozens of feet beyond the edge of a tree’s crown. I once discovered an exposed root following a flood that measured more than 100 feet long from the trunk of a large cottonwood tree.
Should I water
my dead lawn?
Many yards have entered a dormant stage and turned brown, but will recover during the fall rains. Therefore, watering the “dead” lawn will not cause it to green up. However, landscape plants and trees in the lawn have not gone dormant.
Test the dirt around a shrub or tree located in the lawn with a trowel. If the soil is dry for 6 inches or more, a good soaking is in order. Run a sprinkler or soaker hose for an hour or more to allow the water to soak in enough to reach the critical absorbing roots. Placing a sprinkler near the drip line is a good compromise in guessing where the roots are located around deciduous trees.
Some of my trees are dropping leaves
or needles. Are they dying?
Many conifers such as western red cedars, pines and fir trees naturally shed interior needles during the summer and fall. These are needles that are no longer functional. The shedding may be more prevalent during dry summers as the trees attempt to reduce transpiration to preserve moisture.
If the newest or outer growth is dying, then some other problem may be involved. For example, I recently observed a few fir trees that appear as if they have been scorched on one side. This likely occurred during the very warm temperatures of two weeks ago when moisture loss happened faster than the tree could respond to and some needles and small twigs died. Such damage may be covered by new growth next year.
Deciduous trees may also lose leaves earlier than normal as they attempt to reduce moisture loss as they become more stressed. Sometimes such loss can be accelerated if there has been a severe infestation of aphids or spider mites. Such trees generally have normal growth the following year.
Why do certain trees appear to be dying?
The causes may be difficult to determine. However, trees may take several years to react to dry conditions. If their natural defenses against insects have been compromised, bark beetles will attack such weakened trees. These insects are usually the last nail in the coffin and are impossible to treat with insecticides.
How do I protect my trees and
shrubs for the remainder of the summer?
If possible, give them a good soaking once a week for the next month or so until the fall rains return. A high water bill may be inexpensive compared to replacing landscape trees and shrubs.
Dennis Tompkins is a certified arborist, certified hazard tree risk assessor, Master Gardener and urban forester from the Bonney Lake-Sumner area. He provides small tree pruning, pest diagnosis, hazardous tree evaluations, tree appraisals and other services for homeowners and businesses. Contact him at 253 863-7469 or email at email@example.com. Website: evergreenarborist.com.