Sunscald and Sunburn in Plants

By on June 10, 2015

Sunscald in tomatoes

We all know it’s important to apply sunscreen before heading outside, especially on a sunny summer day.  But did you know that plants can get sunburn too?  While you can’t protect them with your sunscreen lotion, there are other ways you can prevent sun damage in your garden.

Identifying Sun Damage

There are two main kinds of sun damage in the plant world:  sunburn (also called leaf scorch), which affects the foliage, and sunscald, which affects the bark.

Sunburn occurs in plants for like it does in people – too much light and heat, with increased risk when dehydrated. But unlike us, the sunburned plants don’t immediately turn pink. The damage can take longer to become apparent, and results in yellow or brown foliage.  If the damage progresses, the leaves die off starting in the areas between the leaf veins. 
sunscald on ash
Sunscald occurs for the same reasons, however in this type of damage the bark becomes cracked and scarred. Sunscald makes the wood more susceptible to infestations of wood-boring insects and fungal infections. In the worst cases, the bark can become girdled with cankers, which restricts the flow of nutrients through the inner bark and is fatal to the plant. Sunscald can also occur on fruits, causing damage to the skin, and makes the fruit more susceptible to attacks by pests and diseases.

Sunblock for Plants

When preparing to plant any new landscaping in sunny areas, prevent sun damage by selecting native plants and plants that are adapted to the light conditions where you will be growing them. If you will be transplanting established plants, avoid moving them into significantly more sun than they are used to.

Mulching around plants can help conserve water, reduce reflective light around plants, and reduce the soil temperature to ease heat stress. Apply a 3 to 6 inch layer of wood chips, straw, cocoa hulls, or other biodegradable material around the root zone of the plants. Leave a few inches space from the plant stem or tree trunk to discourage pests and prevent diseases such as crown rot.

Put up some shade fabric over shorter plants, or wrap the trunk of at-risk trees, when they are getting too much sunlight. Different types of plants need different amounts of shade. Don’t overdo it or you’ll end up with pale foliage and spindly shoots from inadequate sunlight!

For your trees, you can apply a coat of white indoor latex paint diluted with equal parts water to any areas that are not receiving enough shade from the tree’s canopy. Young trees and trees with thin bark such as sugar maples are at the most risk of sunscald and would benefit from a yearly coat of paint until their canopy develops. Proper pruning also helps in sunscald prevention: never prune more than 20% of the canopy in one year to maintain sufficient shade for the bark.

Tree wraps provide an easy alternative to paint for young trees. Simply wrap the over-exposed bark in Jobe’s Tree Wrap or in Spiral Tree Guards to provide shade to those areas. Tree wraps also provide additional protection against some insect and rodent damage. 

As the mercury rises and the days get longer, it’s time to protect your plants and yourself from the sun!

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