As stated above, there are a lot of factors that come into a plant's recovery from heat stress. It can be from a few days to a few months, depending on the severity of the stress and some may not recover at all.
Keep them in a shady spot to give them a chance to recover: even plants that look terminally crispy can often revive and re-sprout with this treatment. Larger pots should be heavily watered, then allowed to drain – one deep watering is better than daily sprinkles.
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.
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.
Some signs of heat related stress on plants include: leaf scorch, leaf rolling, wilting, blossom/fruit drop, sunscald, blossom end rot, and other variable conditions that could be brought on by secondary pathogens. Heat stress adversely affects plant metabolism, disrupting their vital biochemical processes.
If you are dealing with a very hot day, misting in the morning and again in the afternoon is a great way to help control the temperature of your plants and keep them safe and looking great.
Watering plants in 100-degree heat must be done daily, especially if the soil has no ground cover.
If the damage is isolated to a portion of the plant, it can be revived and recover. The focus is on minimizing the damage.
Sun sensitive plants need immediate shade after overexposure to the sun. If the plants are potted, then move them to a covered porch or indoors. If the plants are in the ground, then cover them with a fabric sun screen that is rated for landscaping. Watch the plants over the next few days to see how well they respond.
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.
Extra water now could pull them out of dormancy. These stressed plants may then expend a lot of energy growing a new set of leaves only to be faced with the likelihood of more heat and no natural rainfall. If they do not emerge from dormancy, they will be susceptible to fungal pathogens that grow in moist, hot soil.
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.
What Does Deep Watering Mean? Generally, deep watering means that the soil is saturated to about an 8-inch depth. Healthy plants usually grow their roots down deep. In fact, some plants grow roots that are nearly two feet long for optimal nutrient and moisture uptake.
Adding a layer of mulch around ground covers, shrubs, and trees will keep the soil a couple of degrees cooler while stopping it from drying out. Apply your mulch about three inches thick around the plants, spreading it near the drip line or water source. Ensure to keep it about six inches away from tree trunks.
Cacti, succulents, fiddle leaf fig (Ficus Lyrata), and other plants that prefer dry environments are among them. Although they prefer humidity, watering fuzzy-leaved plants like African violets and piggyback plants (Tolmiea menziesii) is not recommended since the water droplets will mark the surface of the leaves.
Provide shade or use shade cloth during peak sun hours. Consider using drought-tolerant or heat-resistant plant varieties. Improve soil quality by adding organic matter to enhance water retention and nutrient availability. Use water-conserving techniques like drip irrigation to reduce water wastage.
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.
Remove affected leaves to allow the plant to redirect energy to healthy areas. Mulch around your plants to protect the root system, ensuring hydration and shielding from the sun. Avoid piling mulch around the tree's trunk. If your plant is in a container, relocate it to shade during the hottest afternoon hours.