Sunscald: The Hidden Threat to Your Trees

Oftentimes, a crack in a tree's bark is an overlooked issue in gardens or parks. One of the most common causes is extreme temperature shifts. This damage is especially severe in young or thin-barked trees, leaving them vulnerable to long-term health problems. Understanding how and why sunscald occurs is the first step in protecting your trees from this silent but serious threat.

What Causes Sunscald?

Sunscald usually occurs in the winter months. After a cold night, sudden and intense sunlight can cause the outer bark to heat up rapidly, leading to cracks, discoloration, and weakened defenses against disease. The damage isn’t always obvious right away, and it can take years to show as the bark eventually splits open. These weakened areas create an entry point for pests like flatheaded borers, as well as fungal and bacterial infections.

Damage primarily occurs in young, weak, thin-barked trees such as Shumard oak, Chinquapin oak, Live oak, Chinese pistachio, Elm, and Maple.

Does It Kill a Tree?

While sunscald itself typically doesn’t kill a tree, it can significantly weaken it. In severe cases, sunscald can cause branches to die, especially if it spreads into the canopy or covers more than 50% of the trunk. This leads to a noticeable decline in canopy volume and can make the trunk unstable.

The tree will likely attempt to heal over the wound, but if sunscald damage covers more than half of the trunk or causes internal wood to crack and dry out, the tree may not survive. This severe damage can prevent the tree from properly healing, as conducting tissues responsible for repair are destroyed.

Differences Between Sunscald and Sunburn

Direct, intense sunlight can heat unadapted tissues and cause cell death. While both sunscald and sunburn result from excessive sun exposure, they affect plants differently:

• Sunscald: Prevalent on trees, especially after sudden temperature changes from night to day, causing bark to crack or peel. It weakens the tree, making it vulnerable to pests and disease.

  

• Sunburn: Affects leaves and fruits, leading to bleached, scorched, or necrotic spots. It results from prolonged, intense sunlight, usually in dry and hot summer conditions.

  

Symptoms and Identification

Sunscald damage is most noticeable on the west and southwest sides of tree trunks. Common signs include:

• Fissures or splits in the bark – Over time, cracks may split and extend vertically, revealing damaged tissue underneath.
• Bark discoloration – Affected areas often appear lighter than surrounding bark.
• Weak, brittle branches – Weaker and poorly shaded horizontal branches are more susceptible.
• Delayed leafing or dieback – Trees may struggle to produce new growth.

In many cases, symptoms only become noticeable three to four years after planting, when the bark starts to crack and weaken. By the time symptoms appear, the damage is already done, making prevention crucial.

If you look closely at an affected tree, you may notice hollow areas or shallow tunnels in the wood. These are often signs of tree borers, which act as "secondary invaders." At that point, intervention might be necessary.

How to Prevent Sunscald

Since sunscald affects not only the visual appearance of trees but also their long-term health, prevention is key. Here are a few effective strategies:

1. Mulching

Applying a layer of biodegradable mulch around the root zone helps regulate soil moisture and temperature. It protects roots from extreme heat and cold while retaining moisture.

2. Proper Pruning

While trimming trees is essential for health and shape, excessive pruning can expose sensitive bark to intense sunlight, increasing the risk of sunscald. It’s important to prune carefully to maintain natural shading, especially in formative years.

3. White-Washing

Painting trunks with light-colored, water-based indoor paint reflects sunlight, minimizing temperature extremes and reducing sunscald risk. This method is common in some households and also helps repel insect pests.

4. Wrapping the Trunk

Using tree wraps during winter insulates the bark and reduces temperature fluctuations. Be sure to remove the wrap in spring to prevent moisture buildup and fungal growth. This is especially crucial for thin-barked trees.

Young Trees: The Easiest Way to Protect Them

One of the simplest and most effective ways to prevent sunscald is wrapping the trunk with burlap from the ground up to the lowest branches immediately after planting. This barrier helps regulate temperature changes, allows airflow, and provides shade. The burlap cover should remain in place for 18–36 months to ensure the tree develops strong, resilient bark.

Conclusion

Sunscald is a silent threat—easy to neglect until the damage is done. The best time to protect your trees is from day one. A little effort now—like wrapping trunks, providing shade, and smart pruning—can prevent major problems in the future. Think of it as giving your tree a strong start in life. It’s not just about keeping them looking good; it’s about building resilience from the ground up.