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Over the Garden Fence

Frost Cracks

Every season brings new surprises to homeowners. Spring is no exception to this. Finding out the 300 spring bulbs you planted last fall are actually white, not the yellow the plant label said they were. Less enjoyable surprises would be finding out the young trees you planted to replace the Ash destroyed by the Emerald Ash borer have been damaged from the winter weather.

One of the most common kinds of damage is called "Frost Crack".   Frost cracks may not be readily obvious right away, the damage occurs on the south and southwest sides of tree trunks.

Some of our favorite kinds of ornamental and shade trees are most often targets for this kind of winter weather damage. Good examples are young flowering crabapples, fruit trees and some of our maples with smooth bark (at least when young), lindens and really any other thin barked tree is a potential for damage.

While our favorite trees are being professionally grown for us, this frost crack damage is something that occurs once planted in the home landscape. As trees are grown in the nursery, those plants are naturally oriented to rising and setting of sun as well as their northern and southern exposures. As a result of this orientation, the thickness of the bark will vary as you move around the trunk.

That slightly thinner bark will be on the north and east sides and this then becomes the problem later on. When a gardener plants the tree at home, that orientation becomes an unknown. Gardeners can do everything right to ensure transplant success, yet that orientation is out of our control.

So what is causing the actual crack is 'Ol Sol' The sun will warm the trunk on those south and southwestern sides during the day even on a very cold day. The fluids later in the day at dusk will freeze and expand, causing the tissues just below the bark to burst. Damage will usually be from the ground up from anywhere from just a few inches to three to four feet in length.

To prevent this sun crack damage, it is important to wrap the trunks that first winter. By the second winter, the tree will have re-oriented itself and build up that thicker bark on what is now the southern and western exposures.

This summer be on the lookout for splitting bark, a good sign of damage. That splitting bark will be dead and should be cut away to living tissue to aid in the healing process. Callous tissue grows at about ½ inch a year, so depending on how wide the damage is, it will take a few years to heal over. Gardeners can, if they want, continue to wrap the damaged area late in the fall each year, preventing any new tissue from being damaged again until the wound callouses over or a thicker bark develops over the wounded area.

Now back to the 300 white flowering spring blooms. Consider them as cut flowers for the home, office, the local nursing home or hospital.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.