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North Hills Monthly

Summer Heat Can Lead to Winter Woes

Jul 30, 2014 11:19AM ● By Denise Schreiber
Hot August nights—and I’m not talking about the Neil Diamond album from long ago. The memories of last winter’s horrors have finally faded, and now we’re starting to long for a few cooler days and evenings.Image title

Our plants are longing for those days, too. High heat, bright sunlight and a lack of water take a toll on them, and this combination can be especially deadly for them come winter. Plants that normally grow in an established hardiness zone may also be injured if winter conditions are abnormally severe or if plants have been stressed by the environment. Injury is more prevalent and more severe when low temperatures occur in early fall or late spring, when there is little or no snow cover during the winter, or when low temperatures are prolonged.

This is why it is important to deeply water your trees and shrubs on a regular basis. Trees with a two-inch caliper should receive at least 15 to 20 gallons of water a week. That sounds like a lot, but it isn’t. You can apply that amount of water at different times, too—don’t do it all at once.

Wild fluctuations in temperature can be extremely detrimental to plants throughout the fall, winter or spring. We’ve all seen an early spring thaw that makes some plants throw out their spring blooms long before they should, only to be killed by the next drop in temperature. Do not fertilize trees and shrubs after mid-July, and stop pruning in early August so that the plants have time to harden off the new growth; otherwise, plants could be winter-killed.

Sun scald is characterized by elongated, sunken, dried or cracked areas of dead bark, usually on the south or southwest side of a tree. On cold winter days, the sun can heat up bark to the point where cambial activity is stimulated. When the sun is blocked by a cloud, hill or building, bark temperature drops rapidly, killing the active tissue. Young trees, newly planted trees, and thin-barked trees (cherry, crabapple, honey locust, linden, maple) are most susceptible to sun scald.

Trees that have been pruned to raise the lower branches, or transplanted from a shady to a sunny location are also sensitive because the lower trunk is no longer shaded. Often you will see evergreens limbed up like this because some people feel that they need to look like decorations on a train set. Older trees are less subject to sun scald because the thicker bark can insulate dormant tissue from the sun’s heat, ensuring the tissue will remain dormant and cold-hardy. Sun scald can be prevented by wrapping the trunk with a commercial tree wrap, plastic tree guards or any other light-colored material. The wrap will reflect the sun and keep the bark at a more constant temperature. Put the wrap on in the fall and remove it in the spring after the last frost. Newly planted trees should be wrapped for at least two winters.

Bambi and his family will be singing the song of their people soon. The little button bucks have sprouted their first set of antlers and have the timeless urge to rub off the velvet on anything they can—which usually involves your trees and shrubs. Stiff, upright shrubs are more at risk than shrubs that bend easily. All trees are fair game, though, so protection is needed. Fencing around a tree is best to keep the deer from rubbing…and eating. The next best protection is using tree guards that you can purchase from nurseries that allow trees to breathe, but protect them from deer. They look like open mesh, but are actually a very thick plastic. They are secured with cable ties and you can leave them on indefinitely.

Mulching is also really important now. The typical homeowner applies mulch in the spring, when it is actually needed in the fall to keep moisture around plants and to moderate soil temperatures. Two to three inches is all that is needed—make sure that you keep it away from the trunk of the tree to prevent rodents from feeding.