2 Signs of Winter Tree Damage You Won’t Notice Until Spring – and How to Fix Them

Deciduous trees in winter have a different kind of beauty. Their green canopies are gone, leaving only trunks and branches silhouetted against the sky. They seem to be safely sleeping through winter’s worst, but that’s not always the case. Extreme winter weather can damage tree bark in more ways than one.

Winter tree problems often begin with damage to the bark, which is often the result of common tree care mistakes people make without realizing it. Bark is the tree’s protective covering, and when it’s injured, the tree’s vascular system can be put at risk. You can protect your tree trunks from winter weather – and we’re here to show you how. Understanding how to prevent and address winter tree damage will help you keep your landscape trees healthy and vigorous.

Tree Trunk Problems

Nature didn’t create tree trunks just to add vertical interest to your landscape. Think of the trunk as the body of the tree. It’s covered in bark, which protects the tree’s vascular system – the internal pipeline that transports water and nutrients from the roots to the branches.

Both sunscald and frost damage can injure tree bark in winter. The damage isn’t always obvious at first, but you may be in for an unpleasant surprise come spring. Warm sunshine and icy frost – together and separately – can harm bark tissue, and the effects can show up in a variety of ways.

What Is Sunscald?

Extreme winter weather can damage tree bark. How does that happen? Much of the harm is caused by sunscald, and the trees most at risk are younger ones with smooth bark. Mature trees with thick bark are rarely affected.

Sunscald in trees is a bit like sunburn in humans. It typically occurs in late winter, when the sun grows stronger but nighttime temperatures remain below freezing. The south or southwest side of the trunk warms in direct sun – sometimes reaching as high as 77°F (25°C) – then cools rapidly after sunset. Covering vulnerable trees can help protect them from frost cracks, especially young trees growing in exposed sites.

Recognizing Sunscald Damage

Here’s how sunscald works: the sun warms the south or southwest side of the tree trunk. This warmth causes cells that went dormant during winter to become active again. As they reactivate, they lose their cold hardiness, making them more susceptible to freezing injury. When nighttime temperatures fall, the previously warmed tissue can be damaged.

Sunscald injury can produce visible symptoms on the bark, including discoloration and surface cracking. Affected areas may fail to grow properly, creating sunken patches, or the bark may slough off entirely, revealing dead tissue beneath. This leaves the tree vulnerable to pests, diseases, and additional stress.

Preventing Sunscald Injury

While you can’t control the sun or winter temperatures, you can take steps to protect your young deciduous trees from sunscald. This process should begin in late fall.

Purchase light-colored tree wrap from your local garden center, or use a breathable protective wrap designed specifically for young trees. Identify trees with southern or southwestern exposure, and wrap their trunks before winter sets in. The wrap helps shield the bark from extreme temperature fluctuations.

Tree Protection Picks

What Is Frost Damage?

The other primary cause of winter tree damage is frost. This type of injury is easy to spot: deep, vertical cracks in the trunk. It won’t surprise you to learn that this condition is called a frost crack.

While sunscald can sometimes split the outer bark, a frost crack is a far deeper injury, extending into the wood of the trunk.

What Causes Frost Cracks?

The same temperature swings that trigger sunscald can also lead to frost cracks. This typically occurs during repeated, dramatic swings in temperature. As inner wood and bark tissues expand during the day and contract at night, stress builds within the trunk. Over time, that stress can produce a vertical crack that extends deep into the stem. If pathogens enter through the crack, the tree can decline, or even die.

Preventing Frost Cracks

Covering vulnerable trees can help protect them from frost cracks, especially young trees growing in exposed sites. You’ll need breathable burlap screens or frost blankets. Install them when sudden temperature drops or hard freezes are forecast.

Trees have a remarkable ability to heal their own wounds, gradually sealing damaged areas with protective tissue and producing new wood over time. So even if your tree develops a frost crack, it will likely recover.

What to Do if Your Tree Has Winter Bark Damage

If you notice sunscald injury or frost cracks on your tree, don’t panic. In many cases, trees are able to heal the damage naturally over time.

Avoid cutting away damaged bark unless it is loose or clearly dead. Healthy trees will gradually form protective tissue around the wound and seal the damaged area. Keeping the tree healthy through proper watering, mulching, and fertilization will help it recover.

If the crack is severe or continues to widen, it’s best to consult a certified arborist. Large trunk injuries can sometimes weaken the structure of the tree and make it more vulnerable to pests or disease.

Proactive Winter Tree Care

Here are some proactive steps you can take – well before winter – to help prevent issues like sunscald, and frost cracks.

• Keep your trees properly irrigated. Well-hydrated trees are less susceptible to winter injury than drought-stressed ones. Continue to deep water throughout fall and into early winter, stopping once the ground freezes. A tree watering bag, like this Greenscapes product, can help deliver slow, deep irrigation to young trees before winter arrives.
• Mulch helps protect tree roots from drying out and from extreme cold. Apply a generous layer of organic mulch in autumn, keeping it a few inches away from the trunk, or use a mulch ring, like these from Amazon, to help retain moisture and regulate soil temperature.
• Purchase tree guards and keep them on hand. You don’t need to keep trees wrapped all winter, but install guards when needed to protect bark from direct sunlight.
• If you can shade the south and southwest sides of a tree, you can reduce the risk of sunscald. Consider planting shrubs or small trees nearby to provide that protection.