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.
Even your plants that love to soak up the sun need some form of shade to protect them. Make sure you place plants in an area where they'll get at least some shade throughout the day. This will prevent scalding or over-drying, and will help you conserve water as well.
Sun-scorched plants can be cut back and fertilized and should recover with time (planting in the ground would be even better!). However, root rot is usually fatal. It is a delicate balance to keep plants well hydrated, but allow the roots to dry out enough to function properly.
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.
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.
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.
Browning of leaf margins and/or yellowing or darkening of the areas between the main leaf veins are symptoms of leaf scorch. Due to environmental causes, leaves may dry, turn brown, and become brittle. Look for damage to trees and shrubs on the upper portion on the sunny, southern side and on the windy side.
A: I assume your question is about the commonly held notion that full sun on droplets of water will burn the plant. The answer is no, to that question and to yours. (See The Myth of Hot-Weather Watering.) Even so, the best plan is to have plants well hydrated before the heat hits.
Your containers need to be watered every day, especially when temperatures are so high. Sometimes you might even have to water in the morning and the late afternoon like we do in our Garden Center.
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.
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.
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.
Signs Your Plants Are Too Hot
The leaves dry out. Excessively hot plants will dry out faster. The leaves turn yellow. One of the causes of yellow leaves is excessive heat, so this is one thing to consider!
Leaves with scorched margins may look unappealing, but they still help the plant with photosynthesis, creating food for new, undamaged leaves to emerge. Resist the urge to remove scorched leaves.
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.
The best time to water plants is in the morning or evening.
More importantly, watering at these times actually helps the plant retain water. If you water in the afternoon, especially during summer, the heat and sun are at their peak and the plant's water will evaporate instead of absorbing into the soil and roots.
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.
Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants.
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.
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.
Keep in mind that morning sun, which is cooler and less intense, is easier on shade loving plants then the hot afternoon sun. Plants that receive too much intense light will scorch if pushed into too much hot sun.