— Nan Sterman
Have you noticed your plants wilting in the heat? It’s been so oppressively hot that droopy leaves are everywhere.
Here’s what you need to know about plants that wilt: if they look droopy at the end of the day, don’t worry. If they look droopy first thing in the morning, worry. Let me restate that: If they look droopy first thing in the morning, water. It’s all about the water
First understand what causes plants to wilt. Water normally evaporates through tiny pores in plant leaves called “stomates.” Leaves also lose water through stomates via a physiological process called “transpiration.” Transpiration is sort of analogous to human perspiration. Together, evaporation plus transpiration are referred to as “evapotranspiration.”
Like perspiration, when the weather is hot and dry, evaporation increases. We drink to replace the water we lose through perspiration (and exhalation too). Plants replace it by pulling water from soil via their roots.
When you see plants with droopy leaves, you are seeing evapotranspiration outpacing water replacement. Leaves are losing water to the air faster than roots can take it up. At night, evapotranspiration slows down, allowing roots to catch up. So, by morning, a healthy plant’s leaves will be back to normal.
If the leaves don’t look normal– if they are still droopy – that’s the signal that the soil is too dry. It’s time for deep irrigation – run the irrigation as long as necessary to saturate the soil down deep, where the roots are. By day’s end, the plant should be recovered.
Now, there is a point of no return – the point where the plant is so water deprived that it goes into permanent decline. No matter how much you irrigate, it won’t recover. This is one important reason to plant in fall, winter, and spring, when the air is cool. Plants survive transplant much better in cooler temperatures.
This is also why mulch is so crucial. Mulch serves as an insulator that slows the rate at which water evaporates from the surface of the soil. Mulch helps hold in water around those all-important roots.
So next time you see droopy leaves in the afternoon, check back the following morning. When you see droopy leaves in the morning, water.