During excessively hot summer days it's not only humans that can suffer from heat stress. Your plants can suffer from heat stress as well, especially when there is an abrupt spike in the heat. Excessive heat and sun radiation can result in scorched twigs and leaves, inhibit plant growth, reduce germination potential of the seeds, and discolor fruit and leaves. Excessive heat can also potentially lead to thermal death of a plant.
There are a few basic steps you can take to help reduce the potential for heat stress in your plants. When it's really hot, we perspire to cool down our body temperature. The equivalent in plants is transpiration. Plant transpiration increases in hot weather. So it's important to keep yourself and your plants hydrated in hot weather. Ideally, plants should be given a good watering prior to a predicted sudden heat spike to reduce the potential for heat stress.
Adding several inches of mulch around trees and plants will help the soil maintain moisture. It also helps cool tree and plant roots. Plus, there's the added benefit of weed suppression.
Suspending shade cloth or some other fabric above the plants to provide them with shade during extreme heat will help keep the plants cooler and protect tender new growth. And remember to try to stay in the shade if you must do a limited amount of yard work during extreme heat.
A good general rule of thumb is during extreme heat, take precautions to protect both yourself and your plants from heat stress!