Plants do not recognize averages. The ultimate low temperature is more critical, so what guidelines should we use? Microclimates might add a zone or two, but most experienced nursery professionals consider Zone 5b to be the safer designation. It has a range of minus 15 to minus 10 degrees F, which is where the mercury recently dropped in a number of locales in Utah. Of course, if your garden got colder, look for the appropriate plants.

Maps are one thing, and cold winter landscapes are another. While it is impossible to totally determine plant damage at this time of year, you might want to reconsider plant choices. My best advice is to talk to experienced plant people for good recommendations or check out local publications to determine plants that will survive our winter conditions.

This year, two factors are working in our favor to reduce winter damage. One is that temperatures did not go from unseasonably warm to bitter cold. In the last extremely cold winter, December 1990, the thermometer dropped to minus 28 F at my house in Tooele County. A few days before, springlike temperatures had deacclimated plants, and many thousands around the county died as a result.

Temperature extremes can cause severe plant damage. The wild fluctuations from relatively warm to subzero are often fatal to more tender plants. From a plant health standpoint, winters where temperatures cool down gradually and then stay cold until spring are the least damaging.

The second favorable factor is the snow. Some people consider snow to be harmful, but in reality it is helpful because it insulates and protects plants. Pansies and other flowers you put in last fall should be doing well under the snow and will look much better come spring than they would have had there been no snow.

Many people are concerned about the tulips and other flowers that were peeking out from under the soil last fall. The snow also is keeping them from the extreme cold, and they will also likely look good when they bloom this spring.

Now to fruit trees, where there are two concerns: the hardiness of the tree and the hardiness of the fruit buds. While it is impossible to assign an exact temperature to each of these, it is possible to have the temperatures get cold enough in midwinter to kill the fruit buds.

Ranking trees from least to most hardy in terms of both bud and wood hardiness is as follows: almond, peach, cherry, apricot, plum, pear and apple. Keep in mind that within these groups are great variations in the different cultivars of each type of fruit. Peaches may have suffered damage in some areas, but apples and pears should be fine. Other damage will vary according to local conditions.

Other plants that are likely to have problems include hybrid tea roses; broad leafed evergreens, such as euonymus and laurels; and less-tender evergreens, including sequoias, blue atlas and deodora cedars. Wait until spring before making any decisions about replacing plants, since many may discolor badly but recover when the temperatures rise again.

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Larry Sagers is the horticulture specialist, Utah State University Extension at Thanksgiving Point.