Evaluating freeze injury

By Al Cooke, Ag Extension agent
Posted Monday, April 16, 2007

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Pittsboro, NC - I have received numerous questions about the long-term effects of the recent, abrupt change in weather – about a 60-degree change last week. Based on my observations, most of the damage is minimal and temporary. It’s not much more extensive than if the plant had been pruned. The amount of damage, however, becomes more obvious with time. For now, I am not suggesting any action other than wait and watch. Eventually dead shoots will fall off. In some cases, pruning of dead stems may be important later. And there may be more significant damage.

Most of the developing pears, apples, and blueberries will no longer be developing.
But while the damage to the fruits or flowers is permanent, the damage to the plant may be minimal. If the plant doesn’t provide energy for fruit development this year, then growth may be more extensive.

To oversimplify the matter, plants have investments that have been stored over the winter. With the arrival of warm weather, plants diversify their investments; they reinvest some of that stored energy based on the prediction of photosynthesis for more growth. Plants that are established and healthy have more reserves to invest.
Plants that were not healthy or poorly established, may not recover.

An important caveat mentioned above is the phrase “based on my observations.” There may be some serious injury that is beyond my capacity to observe: freezing of the vascular or conductive tissues beneath the bark of trees and shrubs. These vascular cells are the conduits that move water and nutrients between the roots and shoots.
When the temperature dives rapidly from very warm to sub-freezing, these tissues may be permanently injured. But we can’t see that now.

Over the next several weeks or even months, damaged tissue beneath the bark may shrivel up leaving the bark disconnected. Eventually that bark may split or peel.
Unless you’re looking for that injury, you may not see any problem. It may not be obvious until the plant’s demand for water in the summer exceeds the capacity of the damaged portion of the plant to deliver. Wilting and dieback may follow. When we experience a heat wave, it’s difficult to convince people that the problem is a result of freezing temperatures weeks or even months before. I am not aware of anything you can do either now or later to fix it.

This situation is not limited to landscape plants. It also occurs in nurseries. It is possible that you can buy a plant that looks great in April or May even though it has permanent damage from freezing. It may be difficult to explain this in July or August.

I have never been a fan of “guaranteed plants.” Living things can be guaranteed to die, but we cannot guarantee that they will live for any period of time. They require certain resources that a gardener must provide. Some nurseries will guarantee the plant to live for a given time period regardless of how you treat it.
And they just redistribute that expense in their overhead or price structure. Some nurseries will guarantee that the plant is alive when it leaves the nursery - only.

Regardless of which nursery you deal with, you may want to inquire about how they deal with such situations. Growing plants is a risk. When you purchase a plant you buy into the risk. There may be concealed injury that is not obvious.