BY Sarah Busdon
When a person is exposed to too much sun and heat, they can end up with a sunburn, feeling wiped out or worse. This can happen to trees and plants as well. Heat stress is caused when temperatures are hot enough for a period of time to cause irreversible damage to plant function or development. Plants can be damaged by either high daytime or nighttime temperatures and by either high air or soil temperatures.
Very high temperatures cause photosynthesis (process of capturing light energy and converting it to sugar energy), transpiration (evaporation of water from plant leaves) and respiration (process of metabolizing sugars to yield energy for growth) to increase.
Here are a few signs of plant heat stress and things you can do to help your plants:
1. In high temperatures (90-plus degrees F.) some plants will begin to wilt regardless of how much moisture is in the soil. Avoid overwatering! Too much water can lead to fungal diseases. Instead, be sure to provide enough water to maintain the proper soil moisture level. Refresh or add mulch to plants. A 3-inch layer of mulch over a root zone will insulate the roots against the heat and minimize moisture loss through evaporation.
2. Plants will drop a significant number of leaves when they are heat stressed. If this happens, check the water situation and water as needed. Sometimes leaf drop happens as a response to intense heat when the plant can’t uptake the existing water fast enough to support the entire canopy. Some plants may stop flowering in hot weather. They may not flower at all until it cools or they will drop their flowers without developing fruit altogether.
3. Cool-weather crops will “bolt” in hot weather. Bolting is the heat signaling the end of the plant’s life span, which culminates in flowering and seed production. Not much can be done once a plant bolts. Once this happens, you should harvest and use these plants before the flavor is ruined by the bolting process.
4 Tomatoes, peppers, squash and cucumbers may exhibit black spots on their bottoms in hot weather. Blossom end rot is caused by calcium deficiency. The calcium deficiency is usually a result of inconsistent soil moisture. The best solution is to water deeply and mulch well.
5. Plants and fruits can get sunburned. This happens when newly installed plants get shocked by either sudden sun exposure or heat that is more intense than it experienced in its nursery location. You can reduce the chances of plant sunburn by properly hardening off plants before planting them. If the heat is really intense, you can provide temporary shade over the plant as an extra layer of protection.
Gardening in extreme heat should revolve around minimizing heat stress for both you and your plants. Stick to watering and mulching as needed, or do it early or late in the day in order to stay cool.
Sarah Busdon in an administrative assistant with University of Idaho’s Blaine County Extension office. For more information, visit extension.uidaho.edu/blaine or call 208-788-5585.