Extreme Heat Can Take A Toll on Plants - Cleveland County, Oklahoma
Tracey PaytonHorticulturalistCleveland County Cooperative Extension601 E. Robinson, Norman, Ok 73071(405)firstname.lastname@example.org Extreme Heat Can Take a Toll On Plants The metro area has had roughly 17 days peaking at or over 100 degrees. Thesetemperatures have been brutal to the lawn and garden. My lawn actually hurts to walk onit’s so brown and brittle. I also have one of the most xeric plants, a Chaste Tree or Vitexthat is wilting! I’ve gotten a lot of questions relating to heat stress on plants in the pastfew weeks. It’s not uncommon for your plants to wilt, have some browning on theleaves, or die back during these conditions. This is especially true if water is limited oryour plants are exposed to full sun all day. What can you do to help eek your plantsthrough these tough conditions? Apply 1-2 inches or water per week in one application. This amount will tend towet the top 6 inches of soil, which is sufficient for shrubs, flowers, and lawns. However,some plants may need more hydration depending on factors such as exposure, age, soiltype, and water needs of the specific plants. Whenever you water, do it infrequent yetdeeply to encourage the plant roots to move deeper into the soil and help them survivetimes of drought stress. Frequent, small amounts of water will lead to shallow rootsystems more likely to suffer in the heat. If your plants don’t perk up a few hours afterwatering, make sure you’re not watering too much. Both over watering and underwatering will tend to look the same—wilting of the leaves. If you dig a few inches downin the soil and it is very wet, cease watering until it dries out. Also, to be the most
effective and efficient, water before the heat of the day. If you have questions on how towater your plants, call a friendly Master Gardener at 405-321-4774. If you are applying water as above and your plants still look sad, it could be asurvival mechanism. Some deciduous plants (especially trees such as River Birch,Cottonwood, and Willows) will drop leaves in response to high temperatures. This isreferred to as cladoptosis. It is easier for the plant to stop photosynthesis than to try andcompete with the high temperatures and scorching sun. In addition to wilting or dropping leaves, you may see some marginal or entirebrowning of the leaves. This is not uncommon and may be referred to as scorch,however not the type caused by a pathogen. In this case, continue watering regularly andmonitor the plant. If the limbs bend and not break, your plant still has some life left in it.In early fall your plants may bounce back and send out some new growth before dying orgoing dormant for the winter. Bermudagrass lawns love heat. But in extreme temperature situations with low orno water, warm season lawns may turn brown, or go “dormant.” Bermudagrass canremain brown for several weeks before permanent damage is done. If you are watering,fertilizer can be applied monthly until late August on most warm season lawns. It isrecommended you don’t fertilize unless water can be applied immediately to preventdamage. Another option for new plants, or especially the vegetable garden, would be toadd a shade structure. This can be as simple as a tarp suspended above the area you wantto shade. This can sometimes be just enough of a break from the heat and sun to make adifference. Make sure whatever structure you use, that there is plenty of airflow for the
plants. Also, fruit set on tomatoes and other vegetables may cease until temperaturesdecrease. If, unfortunately, you do lose plants due to heat and drought, choose replacementplants that can take the heat and naturally save water. Water rationing and restrictionscould limit the amount of water we are able to apply to the landscape in the future. Thereare many trees, shrubs, annuals, perennials, groundcover, and grasses that are droughttolerant in Oklahoma. See the Oklahoma Proven plant list atoklahomaproven.okstate.edu.*************************************************************The Oklahoma Cooperative Extension Service offers its programs to all eligiblepersons regardless of race, color, national origin, religion, sex, age, disability, orstatus as a veteran, and is an equal opportunity employer.