Are Your Plants Sunburned? How to Heal Them

As temperatures peak in mid-to-late summer and moisture fluctuates, many of us in hot climates may notice our plants responding beyond the temporary afternoon wilt. Like us, plants are susceptible to damage from UV rays, resulting in sunburned tissues.

Even plants adapted to high heat and dry spells can experience sunburn and heat extremes (if the Saguaro cactus in the Arizona desert can show stress, any hardy specimen is at risk in changing conditions). Particularly sensitive are young trees, especially in winter, with direct UV exposure to their bark, and Solanaceae family members like tomatoes, peppers, eggplants, potatoes, petunias, and many more.

If your ornamentals or vegetables show signs of sunburn, there are a few measures to heal and restore them to proper health. With minor damage, they’ll rebound to show fresh growth with care and as the weather moderates.

What is Sunburn in Plants?

Sunburn occurs with leaf and fruit exposure to intense, burning rays, resulting in sunscald. With sunscald, bleached, whitish patches appear on the surface of the leaves and skins of the fruits. The blisters become dry and papery as the tissues in the affected area die. Minor cases occur at lower temperatures and present as yellowish or brownish, crispy spots on the leaves. Edges and between veins are likely to show the damage on foliage.

Leaf scorch is another heat-related symptom that occurs in plants at high temperatures. Leaf scorch can happen in bright sunlight but also in shadier zones; it’s related to hot, drying winds and a lack of moisture. Even in shade, plants may experience leaf scorch due to dry heat. With leaf scorch, the leaves lose moisture more quickly than they can uptake it, and edges become brown and crisp.

With both sunscald and leaf scorch, continued damage makes tissues susceptible to other problems like pests and diseases. Pathogens use the weakened and wounded areas as points of entry to infect produce, foliage, and stems. If you notice signs of sunburn, keep an eye out for secondary issues.

Signs of Stress 

In addition to sunburned patches, the garden may show signs of heat stress prior to or during scald and scorch. Thankfully, sunburned plants can heal. Some plants respond to excessive heat and high temperatures with temporary afternoon heat wilt, when transpiration and water loss cause moisture in leaves and stems to withdraw in conservation mode.

On a peak summer afternoon, hydrangeas, cucurbits, nightshades, and other sensitive, moisture-loving selections will show regular wilting. Normally, they rebound with regular moisture and as temperatures cool in the evening.

Heat stress often occurs in temperatures above 90-95°F (32-35°C) for prolonged periods, but can present at lower temperatures depending on climate and factors like arid heat and wind. When there’s little relief as the sun goes down during heat waves, stress increases. Drying winds play as much of a role in heat stress as direct sun exposure.

Preventing Sunburn

Fortunately, there are a few ways to prevent or minimize sunburn damage. The strongest and most feasible is to provide the best cultural conditions. Make sure the plant is in the right spot for its optimal sun exposure to begin with. A partial shade grower, for example, may be pushing its limits with too much sun in summer conditions.

Climate factors like southern latitudes with hot afternoon rays may be too much for many perennials and crops. Plenty of morning sun (like an east-facing exposure) is best for those who rely on ample sunlight but show sunburn from afternoon intensities.

Cultural Strategies

Other cultural measures set the best foundation for resiliency to sunburn. Providing extra water during summer extremes, as evaporation increases (avoiding oversaturated soils for most crops). Regular moisture creates water-filled stems and leaves and also serves to cool the roots.

Soil preferences are essential for strong roots, as many of our gardens rely on well-draining compositions to avoid soggy situations. Rely on a layer of mulch to retain soil moisture and to regulate soil temperatures.

Build the right nutrient base with a soil test and correct fertilizing. Nutrition maintains vigorous leafy growth, which can protect underlying fruits and new, tender growth. But, avoid overfertilizing, which creates an excess of nitrogen and quick, weak growth susceptible to sunburn and defoliation, as well as pests and diseases.

Fertilizing in hot weather, too, causes problems. Balancing the best soil health for the bed or pot and proper fertilizer protocols for the variety is the best platform for resilience.

Offer wind protection or a sheltered spot for those that show leaf scorch in known breezy zones. Lastly, avoid pruning during peak heat or on sunny days to maintain a leafy canopy. Upper leaves shield lower fruits and shoots from the harsh sun.

Healing Sunburned Plants

Plants can heal from sunburn with the proper care and protection. Other than being unsightly, it rarely kills them, unless a secondary problem takes hold.

Keep Leaves Intact

The first step is a little counterintuitive: let the burned leaves stay in place as long as they show some green. The healthy tissues continue to photosynthesize to support the rest of the plant as it recovers. They also continue to shield the younger leaves and fruits, and clipping them off exposes others to the rays and heat. If the leaves show signs of disease, like dark spots or a powdery coating, clip them off to minimize infection.

For produce, go ahead and remove damaged fruits. This allows energy to go into roots, leafy growth, and further flowering and fruiting rather than continuing to develop the affected yield. Since sunburned fruits are susceptible to fungal and bacterial pathogens, it also helps minimize the spread of disease.

Protect and Cover

One of the easiest ways to heal plants with sunburn is to use a shade cover to protect them during prime conditions. Shade protection is multipurpose. It shields leaves from the sun and cools the roots. It also reduces water loss and internal temperatures.

Shade cloth is one of the easiest ways to screen single shrubs, small trees, beds, and pots. The lightweight fabric screens UV rays while allowing natural light, moisture, and air flow. Use shade cloth as a floating row cover on hoops or stakes, or draped over stems. Cover fruits, especially those that are unripe and developing. Thin bedsheets sub for shade cloth if you have them handy.