THE TREE DOCTOR (aka The Plant Doctor)

Drought Management on Trees & Shrubs

Now that we are in the midst of a drought that rivals that of 1988, we should take some special steps to minimize the effect of drought on our trees and shrubs. Many of the turf areas are rather crispy now and many trees and shrubs are showing signs of drought. Incidently, based on my own personal observations during the drought of 1988, lawns which were irrigated infrequently, wasting precious reserves by cycling in and out of dormancy, died by the end of the season and needed replacement. Lawns which were watered infrequently and received abundant fertilizer were almost guaranteed for doom.  Those lawns which received regular irrigation and those lawns which remained dormant, survived. My own lawn received no irrigation during the drought of ‘88 and came roaring back with the rains. Regardless, don’t forget the trees and shrubs!!!  In my opinion, because I’m partial to trees and shrubs, you can let the turf go, [don’t tell the turf specialists I said this-they never read the CAT Alert anyway.] 

Recognize Drought Symptoms - Don't Overreact!

Drought will manifest itself differently in different plants. Some foliage will droop and appear wilted. Some species, especially birch and cherry, exhibit leaf yellowing and defoliation. Some white pines exhibit totally brown needles at this time. Some of these symptoms are normal during drought stress. Many individuals may mistake some of these symptoms as death in plants; regrettably, many plants may be unnecessarily removed. I strongly suspect that many of these plants will recover, even though they appear dead. Check for live cambial tissue as evidenced by green succulent tissue beneath the bark. Also check for the presence of bud set for 2002. These factors may indicate plant survival.

Fertilization NOT!!

One of the first reactions that many individuals have when plants are under stress is that the plants should be fertilized. Many fertilizers contain high salt indexes and this salt can exacerbate drought problems on plants. In fact, lawns and other plants which were scheduled to receive fertilizer applications should not receive any such treatments unless such plants are receiving sufficient moisture through irrigation.

Prioritize the Irrigation!

Because many lawns are receiving irrigation, people mistakenly believe that they are also irrigating their trees and shrubs. Often, trees and shrubs, especially during drought periods, are receiving very little of the water from lawn sprinklers. In several cases now, people have mistaken drought symptoms of trees for diseases or other maladies in landscapes where the lawns look beautiful. Established trees and shrubs will generally survive long periods of drought without too much problem, but they may become more susceptible to secondary problems such as borers. Trees and shrubs generally require “deep root” watering, which implies getting the moisture into the root zone of the tree or shrub, past the thatch in the turf. There are various methods of deep root watering ranging from “flooding” an area to water injections. Be careful when using a water injection method such as a root feeder, because you may not be getting as much water in dry compacted soils as you think. New transplants should probably receive irrigation priority over well established plants. Conversely, occasional irrigation of a large, irreplaceable, valuable tree or shrub should also be considered.

Mulch Helps!

Previous articles have discussed the benefits of well as the detrimental effects of too much mulch. Mulch can help retain soil moisture in the root zones of trees and shrubs, and is particularly beneficial to new transplants. Apply mulch to a generous area over the roots around the stem/trunk of the plant. Taper the mulch in decreasing depth near the stem (increasing depth with increased distance from the stem/trunk). A good drenching of this “bowl” design will allow retention of water for several days, even during the hottest, driest portion of the season.