You look and see that the leaves on your plants are starting to curl.  You see this when temperatures begin to soar.  Luckily, plants have a natural defense mechanism to survive during a heat wave.  To defend itself and conserve energy, plants will start to fold upon itself.  Hence you see the leaves curling.  Then you see the loss of the plant’s “greenness.” The plant’s color starts to drain.  Then comes the drooping.  BUT, after that, well, there really is no “after that,” because the drooping, caused by an absence of water, means the plant is on its way out.

What Can You DO?

  1. Watering: When a heat wave is predicted, deeply water every plant 24-48 hours before the onset. During a dry spell, water your garden either in the evening or first thing in the morning.  It is important not to water the garden in the middle of the day as this teaches the plants to expect moisture during the hottest point of the day.  This, in turn, could cause them to flop.  You also have the additional problem of a high evaporation rate during a heat wave.  Water is best utilized by plants in the early morning, before the sun and heat ramp up.  Watering in the early morning instead of the evening also allows time for foliage to dry, reduces loss to evaporation, and reduces the chance of fungal infections.
  2. Mulch: Putting a layer of bark or compost mulch down throughout your borders will provide a damp layer of insulation that will lock in well-needed moisture. It is particularly important to cover any surface roots to stop them from burning. So, top off mulch around root zones to three inches, especially around new plants or transplants.  Remember: If plants and soil are dry going into the heat wave, they’ll have little chance of surviving.
  3. Observe: Every day of the heat wave, watch for signs of stress. The first will be leaves curling as the plant begins to conserve water; next, the plant will start losing its green color as photosynthesis declines; then, the plant will begin to droop, as it has exhausted its energy reserves and is able to take up less and less water through its roots. The time between these phases will depend on the type of plant, the intensity of the daytime heat and how cool nights are.
  4. Check the moisture in the soil every day:   Put your fingers into the area around the roots (you can also use a soil moisture meter for this).  If the soil feels wet the entire length of your finger, there’s no need to water.  If it’s damp or less, water right away.  Never let the soil dry out completely. Even with careful deep watering, the soil may be dry again the next day, because plants will use a remarkable amount of water just to survive 24 hours. You’re basically providing life support for the plants until the next significant rainfall or until the heat wave breaks.

Should I fertilize my plants to help them during a Heat Wave?

NO!  Never ever fertilize plants during a heat wave.  The lack of nutrients isn’t the pplant’s problem.  Your plants can’t absorb the fertilizer so the fertilizer either runs off or collects in the soil, which may burn the plant when it resumes its normal functions.