Apply mulch, preferably a reflective mulch such as dry grass clippings. The first line of defense against hot weather and the windy conditions that can dry surface soil is to apply a liberal layer of mulch around the plants. This protects the soil from direct sun exposure, keeping it moist at the surface.
Most plants shut down during extreme heat, so if it is over 100 degrees, it may be best to wait to water even if your plant is stressed. Throw a damp sheet over it, or mist it lightly to bring the temperature down. Mist leaves with a spray nozzle to cool down plant and reduce transpiration.
During really hot weather, water your vegetables at least two to three times a week. Watering the garden deeply is critical. The water must go down, down, down to encourage deep roots and get away from the hot soil surface.
If your plants are in pots, move them indoors or to an area with shade. Place temporary shading, such as shade cloth, over plants to keep them cool and block out the sun's rays. Deep water plants first thing in the morning, if possible. Do not fertilize during times of heat stress.
Some plants died and others were fried by the record-breaking temperatures. Even some that look extremely bad, like rhododendrons and hydrangeas, can bounce back. Burned leaves don't necessarily equal a dead plant, so patience and observation is needed.
Most plants can recover when removed from the heat as long as they are generally healthy and given plenty of water and shade to help them recover.
And most importantly, plants absorb water more readily when they're not under heat stress—a condition that's more likely to occur when the sun is at its peak. So while it's perfectly okay to water plants while they're in full mid-day sun, it's not the most efficient way to go about it.
So, how hot IS too hot for plants? The general answer is around 90 degrees F, with some exceptions to the rule. This means that when temps rise above 90 and remain there for a lengthy spell: Leaves wilt.
Be Consistent
You should check the moisture level around the base of your plants. Determine the watering schedule you need to keep in order to maintain the right level of moisture. Watering every day or every two days doesn't matter nearly as much as consistent watering. Make a schedule and stick to it.
There is a high likelihood that plants are experiencing heat stress if they wilt during the day's hottest period and then revive in the evening or morning. Dried Leaf Margins. Some types of crops dry off the leaf's outer edges to ensure survival.
As the weather heats up and plants reach full size, you may need to water containers (and especially hanging baskets) twice a day.
If you forget or are too busy to water your plants on some summer mornings, you can water them at night. However, this should not be your ordinary watering time. Morning is the proper time for watering plants, though you should keep in mind that not all plants need daily watering.
There are a number of ways to create shade in the garden: by draping bed sheets or specialized shade cloth over hoops, stakes, or other supports, using large patio or beach umbrellas, or even erecting large shade canopies over an entire garden area rather than individual beds or plants.
Cover Plants – Protect plants from all but the hardest freeze (28°F for five hours) by covering them with sheets, towels, blankets, cardboard or a tarp. You can also invert baskets, coolers or any container with a solid bottom over plants.
During periods of extreme heat, leaves curl and plants wilt when roots are unable to supply sufficient moisture to the stems and leaves. This occurs because moisture is evaporating from the leaves faster than the roots can supply it. Wilting for short periods of time does not harm plants.
Most plants grow best in temperatures ranging from 59°–86°F. When temperatures above 90°F are sustained for long periods, plant growth is slowed, and some plants begin to show signs of stress.
Too much or too little water. Too much or too little sun. Poor soil condition. Wrong hardiness zone.
Water your plants in the morning as early as possible. This allows the soil and your plants to absorb more water because in the heat of the day there is more evaporation occurring at the soil surface. Drip irrigation is ideal because it deposits water directly at the soil surface and can be targeted.
The heat from the sun evaporates a significant amount of the water you apply to the plants, which makes it an inefficient time to do it. The ideal time to water is first thing in the morning before it's too hot and the plants have time to dry out.
The best time to water outdoor plants is in the morning when temperatures are usually cooler. This gives the plants time to absorb the water so they can get through a long, hot day. The second-best time is late in the afternoon or early in the evening. Try not to water at night.
It can take anywhere from a couple of days to a couple of months for stressed plants to recover. Recovery time depends on the amount of damage that the heat caused to the plant. If a stressed plant is completely neglected during a heatwave, it can take several months or even be impossible to revive it.