Summer heat and drought can cause serious trouble for trees

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Tree Talk with Joanna Angle

Most of S.C. remains in a moderate to severe drought. The effects of drought on trees can be either short term or long term. Short dry periods might cause wilting, leaf scorch (edges turned brown) and possibly defoliation in hardwoods or dropping of yellowed needles in pines. Generally, healthy trees have built-in mechanisms to cope with short term lack of water.

While defoliation is a drought survival response to lessen moisture loss, the danger it presents is reduced photosynthesis. The tree simply cannot produce adequate amounts of food for present and future needs. Drought-stressed trees are also more vulnerable to pests and are less able to compartmentalize small wounds, making them more susceptible to disease.

Drought threatens trees by killing the fine feeder roots that collect water and nutrients. In most trees these are only 12- to 18-inches below the ground’s surface. As the topsoil dries out the feeder roots begin to die, putting the root system out of balance with the tree’s foliage. Worse, the tree is rendered unable to take full advantage of available moisture when rain returns. This results in branch die-back, especially in the tree’s crown.

Drought persisting over several years can result in permanent damage or even death. It is sometimes hard to determine if a tree has died from drought stress or has just become dormant. When in doubt, allow the tree to stand for another year to see if it revives.

Homeowners should consider watering favorite or especially valuable trees to reduce the stress from drought and heat. Retired Extension Service Horticulturist Marty Baker recommended using soaker hoses “…in a donut-shaped pattern starting about five feet from the base of medium to large trees to about five feet beyond the tree’s dripline.” Allow the water to flow for several hours once every week to 10 days when there is no rainfall, preferably watering in the evening or early morning. Applying a two- to four-inch layer of organic mulch will help conserve this moisture.

Joanna Angle is a 30-year resident of Chester County and a Master Tree Farmer. She has previously directed the Olde English District Tourism Commission, produced and hosted “Palmetto Places” for SCETV and helped establish the Chester campus of York Technical College.