While most of our garden plants need at least 6 hours of full sun to be productive, too much sun, especially when combined with too much heat, can be too much for plants to bear. Problems arise especially when temperatures are over 85 to 90 degrees F.
You can identify if your plants are getting too much sunlight by checking for signs of wilting or discoloration, such as yellowing or browning leaves. Additionally, if you notice scorched or bleached patches on the leaves, it's a clear indication of excessive sunlight.
Move a Burned Plant Into the Shade
If your shrub has been getting too much sun, it will have dried-out leaves with dark or bleached patches. So how do you revive a plant that gets too much sun? Trim the foliage, move it to a shady spot with high humidity and water it well.
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.
For example, hostas that are sufficiently shaded may still have leaf scorch symptoms if weather is incredibly hot and dry (Figure 2). Once leaf tissue is scorched, the damaged areas will not recover; however, minor damage, while unsightly, will not kill the plant.
Many full sun plants thrive under sunny skies from dawn to dusk, but others may need a bit of a break. If a plant is labeled heat or drought tolerant and full sun, it is a good bet it will tolerate even the most intense summer sun day in and day out.
Browning of dead tissue often appears without any previous yellowing, extending into the leaf between the veins. Entire leaves may curl and wither when leaf scorch is severe. Scorched leaves are usually abundant on the side of the plant most exposed to prevailing winds and strong sunlight.
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.
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.
Most plants suffer when the weather turns hot enough for a certain period of time. It causes irreversible damage by way of plant function or development. This isn't merely droopy leaves in the heat of the afternoon; it's things like stunted growth, leaf drop, leaf scald, failure to flower, or failure to produce seeds.
Wilting – perhaps the most common response to exposure from extreme heat. Yellow or yellow-green leaves or entire sections of the plant. Leaves appear to be smaller than normal. Needles on evergreens begin to brown from the tip downward.
Too much or too little water. Too much or too little sun. Poor soil condition. Wrong hardiness zone.
Full sun plants don't necessarily need all-day sunlight, but they generally need at least six hours. Afternoon sun tends to be stronger than morning sun, so if you know you can only offer a plant six hours of sun exposure, plant it in a spot that gets most of its sunlight in the afternoon.
To the gardening world it may have always been considered a fact, but science has never proved the widely held belief that watering your garden in the midday sun can lead to burnt plants.
If anything, it's wise to err on the side of less sunlight—once you're dealing with sunburned plants, there's not much you can do. Since the leaves won't heal and return to their normal color, your best option is to cut off the damaged leaves and move the plant back to a spot with no direct sun.
An area on the leaf turning papery white or tan is usually the first indication of scald on plants (fig. 1). Many of these plants were set in the field after coming straight out of the greenhouse or off the trailer. Before the rains we had a few days of very hot temperatures and intense sunlight.
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.
Although plants do not sleep in the same way that humans do, they do have more and less active times and they have circadian rhythms—internal clocks that tell them when it is night and when it is day. And like many people, plants are less active at night. When the Sun comes up, however, they awake to the day.
“Full sun” definitely means at least six hours per day, but some plants such as vegetables really need eight to ten hours per day. “Partial sun” or “partial shade” means that the plant needs 3-6 hours of direct sun per day. The terms sometimes are used interchangeably.
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.
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.