Advice for Keeping Trees and Shrubs Healthy in Drought and Heat

The summer of 2012 has proven to be a tough one when it comes to weather. Most of the country has been abnormally dry, according to the U.S. Drought Monitor. The NOAA National Climatic Data Center also reports that 55% of the country is in at least a moderate short-term drought, with 39% of the country in a severe to extreme drought. It also turns out that this summer is the third hottest on record since record-keeping began in 1895. You can see that it has been a hard season without even mentioning hurricane Isaac and the Derecho storm that left a 700 mile path of destruction across the Midwest and Mid-Atlantic.
Leaf showing response to drought.

Detecting Drought Damage To Limit Stress

We often easily see the damage caused to trees, shrubs, and other plants after a storm. But the damage caused by drought and heat can be just as damaging as storm damage, and often, the damage is already done before symptoms can appear.

Damages from drought and heat go hand in hand; when paired together, the combination can cause even more intense injury. Newly planted trees (less than three years) are most susceptible to drought and heat damage, but even established trees can succumb to their effects.

It is important to catch symptoms early to limit the damage done by these stresses. It is also important to return trees to good health ASAP and prepare appropriately to avoid winter damage in areas where that is a concern.

That is why this year, Extension Agents and Master Gardeners here in West Virginia were on the lookout for trees and shrubs suffering from drought stress, something most homeowners don’t often associate with their trees’ poor health.  An early dry period in March, coupled with summer heat and drought, set the stage for a multitude of concerned homeowners.

Looking for Symptoms of Heat and Drought Stress

As we helped people limit the damage to trees and shrubs by drought stress this summer, we encouraged them to look for:

  • Wilt: The earliest symptom of stress in plants is leaf wilting due to the loss of turgor pressure.
  • Shorter than normal twig growth: Shorter than normal twig growth, small leaves, and overall poor growth can result from drought and heat stress.
  • Plants that shed leaves early: Plants will shed leaves early to reduce surface area to reduce areas that can lose water. Some trees, such as yellow poplar and sycamore, respond to drought through abscission, where leaves change color then fall during the summer. In severe or rapid-onset droughts, leaves may fall while still green. Other trees, such as dogwood, will cope with a process called senescence in which leaves wilt, die, and then fall.

Unfortunately, severe and prolonged drought or heat can cause long term damage or even death in trees in plants. Even moderate stress can reduce growth and make plants more susceptible to pests and diseases. That is why it is important to identify the symptoms and treat them appropriately – because sometimes just adding water to a drought-stressed tree is the best medicine.

Advising what to do (or not do) for drought-stressed plants

We cannot control the amount of water that falls from the sky, so we often offer the following advice:

1) Be on the lookout for early symptoms of drought stress, such as those mentioned above.

2) If damage is light to moderate, simply watering your trees and shrubs can bring them back to health. If drought has been prolonged, a longer watering regimen may be required. However, recovery may be slow, even when sufficient water is restored. Large trees may take an especially long time to recover, as water will need to make it from the roots to the tips of the branches and all the spaces in between.

3) If heat stress is also an issue, we advise people not to fertilize trees until stress is alleviated. Processing nitrogen requires the plants’ use of stored food energy, which is problematic when respiration is abnormally high and nutrient transport is low. Salt-based fertilizers can also cause root damage when soil moisture is limited.

4) Consider drought-tolerant trees when making your next landscape selection.  We shared this drought tolerant tree list from the University of Tennessee with people who were hoping to make their next landscape selection.

So tell us….

Have you experienced drought or excessive heat this year or in the past few years? If so, how did you deal with drought and heat in your garden?

If you’re an Extension Agent or Master Gardener, tell us what kind of advice or resources you used to help people cope with drought in their landscape?

by John Porter
WVU Extension Service Agriculture Extension Agent
Charleston, WV