What is heat stress?
Heat stress occurs when temperatures are sustained over a sufficient period of time as to cause irreversible damage to a plant’s functions and growth. Plants can be damaged by high day temperatures as well as high nighttime temperatures and by high air temperatures as well as high soil temperatures. A plants’ temperature typically runs just above air temperature, the risk of heat stress for plants increases substantially at temperatures above 85 degrees.
High daytime temperatures above 85 degrees can cause direct damage to plant tissues, or indirectly by creating deficit in the plant/water ratio throwing off a plant’s transpiration rate. Transpiration is comparable to sweat in humans, it’s the way a plant stays cool. When temperature climb a plant may utilize more water than is available when this happens the plant is not able to sustain its cooling mechanisms and foliar collapse (wilting) is the first major symptom, followed by browning and defoliation. If left unnoticed heat stress will escalate to a decrease in photosynthesis, increased respiration (utilization of plant sugars), a slowdown of transpiration and ultimate starvation as the plant tries to compensate for lack of food reserves. Adding hot wind hastens the process of the plant’s demise. Heat stress also increases a plant’s vulnerability to pests, disease and other environmental stressors.
Cool water…
This past week the temperatures have been in the high 90’s and I’ve had to revive my wilted Sweet Potato Vine more than once. A bit of water quickly revives a wilted plant within minutes allowing it to resume its normal rate of transpiration, but if left unnoticed heat stress can do irreversible damage to tissues. Wilting is the first sign that plants are overheating- take heed, it is at this point that plants can still be saved.
What can I do to help my plants handle the heat?
- Plant using drought tolerant/Native plants.
- Mulch around plants and trees, mulch lowers soil temperatures and helps to keep temperatures more even.
- Mulch decreases evaporation of moisture from soil
- Water should be applied to thoroughly moisten the root zone, the amount will vary by the size and species of plant.
- Carefully check the root zone to determine the moisture level of the root zone before applying water.
- Well established plants will need less water during warm summer months than newly established plants.
- Mixing humus into soil that is sandy or clay heavy will aid in retention of water.
- Partially shading with arbors or trellises and utilizing ground covers (to help absorb heat) are also good ways to help your plants cope with the heat.