It usually shows up in February or March, on a tree that looked fine at Christmas: a long, vertical crack or a dry, sunken patch of bark low on the trunk, always on the side facing southwest. Homeowners in Melissa, McKinney, and across Collin County often assume a mower hit it, or that the tree is dying from the roots up. More often it is sunscald, a winter injury that has nothing to do with summer heat, and it mostly hits young trees in their first few winters in the ground.
Why the southwest side, and why winter
On a clear, cold winter afternoon, the low sun warms the southwest side of a bare trunk well above air temperature. The cells just under the bark wake up and lose some cold hardiness. Then the sun drops, North Texas temperatures fall fast, and those warmed cells freeze and die. Repeat that cycle over a few weeks and the bark over the dead tissue dries, sinks, and splits lengthwise.
Young trees are vulnerable for two reasons. Their bark is still thin and smooth, so it offers little insulation, and a nursery-grown tree spent its early life shaded by neighboring trees, then gets planted in an open yard with full afternoon sun on the trunk. Dry clay soil adds stress: a tree going into winter short on water has less reserve to wall off the injury in spring.
Which North Texas trees are at risk
Thin, smooth bark is the common thread. Red maples and Freeman maple hybrids are the classic cases here, along with fruit trees, young Shumard and Texas red oaks, Chinese pistache, lacebark elm, and redbuds in their first years. Newly planted shade trees of almost any species can scald in the first two or three winters, before the bark thickens and the lower canopy starts shading the trunk.
Mature trees rarely scald. Thick, furrowed bark insulates, and a full crown shades its own trunk. If you see a long southwest crack on an older oak, check our guide to bark peeling on Texas trees — on a mature tree the same-looking split can point to hypoxylon or lightning instead. Any pruning of damaged oak wood still needs to respect the oak wilt window covered in our trimming and pruning service guidance.
How to tell sunscald from other bark damage
Location and shape do most of the work. Sunscald is one patch, low on the trunk, facing southwest, running vertically, with bark that looks dry, discolored, then papery and loose. A mower leaves a ragged wound at ground level, often on more than one side. Borers leave small holes and sawdust. Peeling at the base, black fungal mats, or mushrooms at the root flare point to disease or root trouble, not sun.
Check how much of the trunk is involved. A patch covering a quarter of the circumference or less, on a vigorous tree, usually calluses over. A split wrapping halfway around a small trunk, paired with dieback the following summer, is more serious and may need a closer look before you decide between nursing it along and planning a removal and replacement.
How to protect a young trunk
Prevention is cheap and it works. Put a light-colored trunk guard or breathable wrap on in late fall, from just above the root flare to the lowest branches, and take it off in early spring. Light color reflects the afternoon sun and keeps bark temperature steady. Leave it loose, and check under it over winter for moisture and insects.
Do the basics around it, too. Keep 2 to 4 inches of mulch over the root zone, pulled back from the trunk, and water deeply before a hard freeze when the soil is dry. When you plant in fall, set the tree so its root flare sits at grade in the clay, not buried. Homeowners in McKinney and other new-build areas see this often, because builder trees go in young, in full sun, with little canopy of their own.
What to do if the bark is already cracked
Do not paint it, fill it, or cut loose bark back to a tidy shape. Leave the wound alone except for bark already completely loose, and let the tree roll callus over the edges. Keep up deep watering through the next summer and keep mulch in place. Most young trees with a modest patch recover, though the trunk may carry a visible seam for years.
Watch it the next season. Full leaves, normal growth, and callus edges creeping inward are good signs. Expanding dead area, oozing, or dieback on the same side are not. If you are not sure which way it is headed, get an on-site assessment rather than guessing — a failing young tree is far easier to replace in fall than in July heat.
Common Questions
What does sunscald look like on a young tree?
Look on the southwest side of the trunk for a vertical patch of bark that is discolored, sunken, dry, or split lengthwise. On thin-barked trees the damaged area may peel away from the wood in late winter or spring. The rest of the trunk usually looks normal, which is why the one-sided pattern is the key clue.
Which trees get sunscald in North Texas?
Young, thin-barked trees are hit most often: red maples and their hybrids, fruit trees, young red oaks, Chinese pistache, and newly planted shade trees of almost any species in their first few winters. Mature trees with thick, furrowed bark and a full canopy shading the trunk are rarely affected.
Should I wrap a young tree trunk for winter?
For a young thin-barked tree, yes, for its first two or three winters. Use a light-colored, breathable trunk guard or wrap from just above the root flare to the lowest branches from late fall through early spring, then remove it. Check it as the trunk grows so it never binds, traps moisture, or hides insects.