7 Signs Your Garden Plants Are Getting Too Much Sunlight

Sunlight is a basic requirement for most garden plants, but some gardeners overestimate (or ignore) the sun needs of their plants, resulting in what plant scientists call photodamage. Too much sunlight is one aspect of light stress (the other is not enough sun), and it's easy to confuse light stress with heat stress since the conditions have overlapping symptoms. Heat and light actually influence each other in a stress situation, and plants can suffer both conditions at once. Heat stress and light stress both affect photosynthesis, but in different ways. Photodamage occurs when too much energy from the sun disrupts the normal function of PSII, an enzyme involved in photosynthesis. The eventual result is cell death.

The intensity of the sun is also a factor in light stress. If you observe any symptoms of too much sunlight such as wilting or curling leaves, try relocating plants to a spot where they'll receive the less intense morning sunlight instead of the burning hot afternoon sun. Consider also creative ways to shade your plants from the brutally hot sun.

Too much sunlight may be why your garden plants are wilting in the summer heat. Wilting is a sign your plant lacks the vigor to execute its normal functions. It can also indicate the plant is protecting itself with a temporary, adaptive wilt that exposes less of the leaf to sunlight to reduce water loss. To check for this possibility, take a look at the same plants at night or first thing in the morning to see if they're still wilted. If so, consider providing a shade cloth.

Just like people, plants can get sunburned when receiving too much sunlight. This symptom appears as brown, yellow, or white areas on foliage. You may have a shade-loving plant in a spot with too much direct sun, especially if receiving six or more daily hours of it. You'll be itching to remove the damaged leaves, but consider leaving them to provide shade for the rest of the plant. Thankfully, it's not difficult to learn how to salvage your sunburnt plant.

In a classic case of broken photosynthesis, excessive sunlight can cause leaves to fade, looked bleached out, or turn yellow. The chlorophyll that gives leaves their green color has broken down. Moving the plant to a shadier location is the best solution. Like other symptoms of excessive sun exposure, yellowing leaves can have other causes. Because one of those causes is the fungal ailment called blight, yellow leaves should be removed if the cause it unknown or determined to be blight.

Curling or cupping leaves can be a sign of photodamage from too much sun. Leaves may also change their positioning in response to sunlight, even reversing themselves from the sun to protect themselves from the intensity of light. You can move them to a spot with less intense sunlight or provide a shade cloth. Be aware that too much sun is not the only reason leaves curl; leaf curl can be caused by insect damage and herbicide use. 

When plants drop leaves from too much sunlight, they are probably suffering extreme stress. Leaf drop is sometimes associated with sunburn and leaf scorch; sunburned leaves may drop off before the end of the growing season. It's likely that photodamaged plants don't put their energy and nutrients into repairing leaves and instead just let them drop off. Since dropping leaves indicates a high level of stress, it's a good idea to get these plants into shade right away.

Excessive sunlight can cause plants to respond by modifying their growth. The photosynthesis process that experiences damage when a plant receives excessive sunlight can trigger a plant to stunt or slow its growth. It can also result in smaller leaves and reduced production in fruiting and flowering plants. Stunted growth is also associated with deficient nutrition or poor soil, so assess your plant carefully to determine whether excessive sunlight or another cause is responsible. Move it into shade if you determine light stress to be the cause of stunted growth.

Too much sunlight affects a process called photoperiodism in some plants that cues them on when to set flowers. Short-day plants won't flower if they are exposed to more than 12 hours of sunlight daily. Though, the amount sunlight these plants get is less important than the hours of uninterrupted darkness they get; 12 hours is recommended. Photoperiodism also affects production of vegetables and crops. Soybean, for example, is a short-day plant that will want fewer sunlight hours and more hours of darkness.