Freeze Damage

The cold weather of the last week has caused some significant damage to new vegetative tree growth across much of the Reno, Sparks and Carson City region.  Many deciduous including oaks, ash, maples and aspen have had their new spring growth killed by the freezing temperatures. Leaves on many trees and shrubs can be damaged by the low temperatures.

What will happen to freeze-affected trees? The answers vary…

Freezing of new leaves will damage the trees slightly. It will set them back and possibly weaken them. Other effects depend on the health of the tree prior to a dramatic temperature change. Healthy trees are able to store around three years worth of energy. If the tree was vigorous and healthy last year, it will put out a new set of leaves from what are called adventitious buds. This “secondary” growth often is weaker than the primary growth put out first, so expect to find small branchlet loss in high wind storms during the summer. The secondary growth also may come out in a bushy or tuft-like pattern called “witches brooming.” The shape and form of these trees may look a little different for a couple of years. If the particular tree in question was declining prior to this temperature drop, expect to see further decline. Trees in this situation have less stored energy and may not recuperate as well as their counterparts. If a tree damaged by freeze has not re-leafed by June 15th, it probably never will.

Tree owners can’t do much to undo Mother Nature’s blow. Our crews will typically prune out dead branches during summer and we do not “baby” the trees with too much water. Overwatering in a heavy clay soil (which most of us have in abundance) will lead to oxygen starvation in the root system. The best rule of thumb for tree watering is: “deeply, less often”.

Your turf will benefit from this watering rule of thumb, too. If the tree is watered with the lawn, try to accustom the lawn to receiving water less than every three days. Resist fertilizing until midsummer, but do it before July 30. Fertilization is not a must. Most trees in lawns receive enough.

Your best bet is to let those freeze-damaged trees recover on their own.

Among those trees are colorado spruce, green ash, honeylocust, and hackberry. These three trees have leaves just beginning to emerge fro the bud, which is the prime stage for freeze damage. Other trees and shrubs that leaf out earlier, such as crab apples, lilacs, linden, silver maple and Siberian elm, are not damaged, as their leaves are “older” and more hardy. Was your tree damaged by a April freeze? If the young leaves are blackened, shriveled and dry as a bone, the answer is, yes. The answer also is yes if, during a present hot spell, leaves are dropping prematurely.

Most hardwoods are very resilient. If they are reasonably healthy, their dormant buds will become active and eventually they will reform new leaves, and by mid summer if will be most difficult to see that they were damaged. Most likely, the greatest damage will be some loss of growth and a slight reduction in health and vigor because of that lost growth. If the tree was marginal in terms of health and vigor, the damage may be more significant, and in a very few cases, cause branch dieback and in the most severe cases even tree mortality.

Some of the conifers have also been affected. Most of the pines do not appear to have suffered significant damage. However, the spruces and Douglas fir have suffered the most, with significant dieback of the newly formed shoots and needles. This loss is more significant than the loss of growth with deciduous trees because conifers have fewer dormant buds.

However, most conifers will recover and may in some cases put secondary growth later this spring.  In some cases, with young trees in particular, the needle and twig loss may be sufficient to cause mortality.  Many of the conifers are also able to survive the frost damage because different parts of the tree are at different stages of growth expansion; earlier stages are more tolerant of cold conditions than later stages.