August: Dealing with the Late Summer Heat

The unrelenting heat of late summer is here and nowhere do we notice it more than in our gardens. The soil can dry out and crack alarmingly fast. Even with consistent watering, plants can become wilted in the intense sunlight. 2016 was the eighth highest August recorded, and although this year’s August is predicted to be more precipitous and to have slightly lower temperatures than usual, the spouts of extreme heat can affect the plants in your garden. Some plants may wilt and others (leafy greens and lettuces) may bolt, but all in all, there are ways to manage the heat with a few preventative measures.

But first, let’s say your plants are already showing signs of wilting: leaves curling in and drooping to reduce the surface area exposed to the harsh sun. How can I effectively revive my plant? You may ask. Honestly, it is as simple as watering immediately and then watering again at night when temperatures have cooled. If the plant re-erects itself, it should be fine. However, if the plant remains wilted after a full night to cool, your plant may be beyond the point of no return. Mostly likely your plant will die entirely or most of it.

(Figure 1) Basil plants showing signs of wilting

An effective way to prevent such drastic wilting is to try to control the soil temperature and moisture—three to six inches of mulch is an ideal method for holding moisture in and keeping soil temperatures from becoming unbearable for the plant. Exposed soil under intense sun rays can become dry and brittle in a matter of hours, and even with continued watering, the evaporation rate may be too quick for the plant to soak up enough water. Laying down a mulch layer of straw or other compost, chopped leaves, wood chips, or grass clippings now (at the beginning of August) can insulate and protect soil “from drying and hard baking effects caused by the evaporation of water from soil exposed to hot sun and winds”(Texas A & M AgriLife Extentsion). With more moisture contained in the soil, your plants will have a chance to “drink up” more of the water and to tolerate the intense heat.

(Figure 2) Three types of possible mulches

Some garden plants react differently to the late-summer scorch. Leafy green vegetables such as Lettuce, and Spinach will bolt very quickly in the heat—bolting is when the plant begins to produce flowers, going to seed and abandoning leaf growth due to soil temperatures reaching above a certain level. The plant is essentially going into survival mode; thinking that it will perish due to the heat, it goes to seed as quickly as possible. Kale, Chard, Broccoli, and Cabbage will also bolt but not as immediately as spinach and lettuce (note: these make ideal cool-season season crops).

Providing shade for these plants will help prevent bolting from happening. Like the mulch method, shading helps preserve water in the soil and keeps the plant strong enough to tolerate the battering heat. Shade cloths are available in different opacities, letting a certain amount of light to break through its fabric. For higher temperatures, use a shade cloth with more coverage, and for lower temperatures, use a shade cloth a higher light transmission. Remember that a shade cloth SHOULD NEVER BLOCK OUT THE SUNLIGHT ENTIRELY. Creating a low canopy over your plants using garden stakes should do the trick!

(Figure 3) Example of using a shade cloth to protect Swiss Chard

Keep in mind, it is always good to be aware of how late summer is expected to play out in your area and to take preventative measures that way. If your plants are growing healthily and not showing any signs of wilting, and if the foreseeable weather seems rather temperate, you may not need to lay down mulch. Bottom line: take preventative measures when they seem necessary—keep a close eye and all should pan out well. Just because it is August does not mean that wilting is a guaranteed occurrence. It just means this is the time of year when plants suffer from it the most.

Folks also become discouraged this time of year because of the stresses of the final stretch of the warm-season, but we always suggest to focus on your successes and wait patiently for harvest to come and to look forward to cool-season gardening that is right around the corner!