Guide

Look closerPlants

Frost cracks and frost ribs on tree trunks

November to March

Some tree trunks carry a long vertical seam or raised ridge called a frost crack or frost rib. It forms where the bark split open in a past cold snap and the tree grew new tissue over the wound.

Why this time of year

With the leaves down, check trunks on the south and southwest sides of sunny trees, where these seams most often form. A seam is a record of earlier winters, and a sharp winter temperature drop can open it again.

How to notice it

  1. Walk around a maple, ash, oak or apple tree and look at the south and southwest side of the trunk, usually about two to five feet up.
  2. Look for a straight up-and-down line, either a narrow seam or a raised ridge running along the bark.
  3. Look at the edges of the seam for a thick, rolled lip of new tissue where the tree has been healing the wound.
  4. Compare with the north side of the same trunk, then with a neighboring tree. Not every tree has one.

Try this with kids: Draw the longest straight up-and-down line you can find on a trunk. Does it have a bumpy lip along its edges?

Phrase to know: A “frost rib” is a raised ridge of healing tissue that builds up where a frost crack opened and closed again over several years.

Safety

  • Look from the ground and keep hands off loose or splitting bark. Do not paint, pry or peel a crack open; it can harm the tree.
  • Stay out from under large cracked limbs in wind or ice.

Sources

  • gov.mb.caManitoba Agriculture: successive cracking and healing over years forms frost ribs; cracks may heal in summer and reopen in winter; late winter and early spring timing.
  • bygl.osu.eduOhio State BYGL: a closing crack can leave a raised ridge or bulge; callus along edges; can reopen in later cold events or years; temperature drop after sun.
  • purdue.eduPurdue extension: cracks typically on the south side between two and five feet up; after several growing seasons most trees heal over, callus makes them look wider; may be heard on a cold late-winter morning after a warm spell; exact cause not known for sure.
  • homegarden.cahnr.uconn.eduUConn Home and Garden: frost cracks are vertical openings, most often on the south or west side exposed to sun; susceptible species include apple, ash, maple, oak, walnut.
  • montana.eduMontana State extension: frost cracks are vertical splits in trunks and bark after severe rapid winter temperature changes; south or southwest side; maple, birch, apple, ash susceptible.
  • extension.illinois.eduIllinois extension: sun warms the south and southwest trunk, then fluids freeze at dusk; cracks may not be obvious right away.

Checked against these sources on October 20, 2026.

In the guide for November, December, January, February, March

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