Of course, we expect summer to be hot. Still, extreme temperatures over prolonged periods can really stress plants in our landscapes. Be mindful of the effects of extreme heat on various tasks in your garden and take care to avoid overheating yourself. Some activities will need to wait until temperatures are a bit more moderate.
Like us, plants tend to slow down when it gets too hot outside. Temperatures higher than 90 degrees can impede the chemical processes in plants and put a hold on regular growth. The first defense against stress damage is for the plant to shut down and try to maintain its status. Plants might quit blooming or abort fruits and blossoms.
During extreme heat, avoid activities in the garden that accompany plant growth such as applying fertilizers, pruning, or planting new plants. Also, avoid applying chemicals when it is sweltering outside. For instance, some labels will indicate not to apply the product when it is more than 80 degrees. Ignoring temperature warnings when using pesticides can cause more damage to your plants than whatever pest you are trying to control. Avoid applying herbicides that can readily volatilize. Some herbicide applications will be ineffective if the weed is not actively growing enough to take up the product as it is intended.
Various heat stress symptoms might become apparent in your garden this week. The most familiar and obvious sign is wilting. The lack of water pressure in the plant causes it to droop. The longer a plant remains wilted, the more difficult it will be to recover. Fruits and vegetables might experience sunscald. The surface of the fruit might appear bleached, discolored, sunken, or hardened due to sun exposure. Sunscald can also affect the surface of leaves, turning them papery-white or tan. Large-leafed plants might experience a dried-out or burnt appearance on the leaf margins.
Combat heat stress with water, mulch and shade. Water deeply in the mornings and as needed to combat wilting. Use mulch to keep moisture from evaporating from the root zone and to insulate the soil from temperature extremes. If possible, move containerized plants out of full sun locations to give them a break in the shade. It’s weather like this that really makes me appreciate drought and heat-tolerant plants!
A course and exam for those needing their initial private pesticide applicators license will be June 22 in our office. Pre-registration is required. A free webinar titled Make Your Apps Count will be noon to 1:30 p.m. July 20. Visit the online calendar here to register for these and other upcoming extension events and classes: calendar.clemson.edu.