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.
As long as there is some green foliage or even if only parts of some leaves are green, your plant should eventually make a complete recovery. It is not a good idea to detach dead leaves from a burned plant because those leaves may be shading healthy foliage that could also burn when suddenly exposed to all-day sun.
For heat-stressed plants, the road to recovery could take anywhere from a few days to a few months. The time needed to recover from stress is proportional to the severity of the damage.
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. Water evaporates into the atmosphere more quickly in high heat, draining a plant's reserves.
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.
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.
Overly dry soil is a sure sign that plants will develop heat stress. Water is essential for plants to live. During a heat wave, correct watering is even more important. Early-morning or early-evening watering is the best time to provide moisture to all your plants in the garden or landscape.
Once leaf tissue is scorched, the damaged areas will not recover; however, minor damage, while unsightly, will not kill the plant.
I've been watering! Potted plants that are completely dried out and crispy could either just have gotten fried by the sun's intensity or have potentially been overwatered. Sun-scorched plants can be cut back and fertilized and should recover with time (planting in the ground would be even better!).
In general, a heat-stressed plant will have leaves that are yellowed or exhibiting some brown spotting. This is usually accompanied by wilting. They may look burned in some places, particularly if they are also receiving too much light.
In times of extreme heat, 1-2 times each week may be necessary. Know your plants though! Some plants prefer almost zero water during summer (manzanita, Ceanothus, madrone and cistus) and others wilt even when they have ample water (hydrangea, rhododendron). So adjust watering accordingly.
Unfortunately, there's no aloe vera to put on your plant's sunburn, and it won't eventually fade into a tan. “If you find your plant has been burnt, it is best to cut off the damaged leaves or trim them if you can,” says Steinkopf. “They will not heal or turn green again.”
Scorch symptoms may differ between plant species, but it typically appears in July and August as a yellowing between leaf veins and along leaf margins, and a browning on the tips of leaves. Since these leaf parts are the last to be supplied with water from the roots, they are usually the first to be affected.
While you cannot control the weather and there is no “cure” once the damage has been done, there are steps that can minimize the effects of leaf scorch. Good cultural practices that improve general tree health and promote good root growth will reduce the risk and severity of leaf scorch.
To revive the plant, you can soak it in water and then adopt a predictable watering schedule that uses the same amount of water each time. Remove dead leaves: Improper care may cause most leaves on the plant to die, and it's usually best to remove leaves that have become entirely brown.
In hot weather you need to water in the mornings when it is cooler. This will allow more water to reach the root system before it evaporates in the heat. There may be times when you cannot schedule watering in the morning. In this case, water the plants in the late evening before bed.
During extremely hot weather (daytime temperatures above 90F and nighttime temperatures above 70F), try to water daily or every other day. In a 10x10-foot garden, this would mean giving your plants 8 to 9 gallons of water each day.
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.
Focus on plants that love the heat.
These include: tomatoes, eggplant, melons, peppers, malabar spinach, cowpeas, and lima beans. Sweet potatoes, okra, and southern peas can handle the most heat.
The best time to water your garden in summer is from 6 am to 10 am—before the heat of the day sets in, giving your plants plenty of time to drink up and any moisture on the leaves to dry off before nightfall. What is this? If watering in the morning isn't possible, the next best time is from 4 pm to 7 pm.
On a hot, dry day (or after several days with no rain or watering), transpiration causes more water to be lost than is coming in, and the water balance within the plant can get thrown off. The dehydrated collapsing cells in the leaves and stems can no longer remain erect, and the plant begins to wilt.