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Most apples are relatively cold-hardy. However, a more important factor to consider is when fruit ripens. In areas with shorter growing seasons, apples that require long growing seasons to ripen are not appropriate.
In areas with the shortest season, summer ripening apples may be the only option. Table 1 is organized in order of approximate fruit ripening dates. Refer to it to find appropriate apples for your area. Additionally, Table 2 lists frost information for many areas of Utah. It includes average length of frost free days as well as average first and last frosts. Apples tolerate some frost. Some believe that light frost additionally improves flavor. Keep in mind that apples should ripen at the same approximate time or before the average last frost in your area.
Overall cold hardiness is additionally important. It is determined by the minimum temperature that a plant can tolerate. The United States Department of Agriculture has developed a uniform system that gives information on average minimum temperatures in a defined area. These areas are designated as zones using a number system. Much of Utah's Wasatch Front is currently included in zones 5 or 6. Zone 5 minimum average winter temperatures are between -10 and -20 F°. Zone 6m is between 0 and -10 F°. Utah's colder mountain valleys are generally included in zone 4, having average minimum winter temperatures between -20 and -30 F°.
Cold hardiness is listed by zone in Table 1 for specific varieties. For more specific climate information for your location, visit the Utah Climate Center http://climate.usurf.usu.edu/.
A microclimate is a defined small area with a slightly different climate than surrounding zones. Microclimates may be warmer or colder can and impact plant survival and performance. For example, trees planted near the south and west sides of structures may bloom earlier due to increased reflected heat exposure from afternoon sun.
In certain situations, earlier blooming makes trees more susceptible to frost damage. However, increased heat realized from this sort of exposure may be more amenable to growing varieties that may not otherwise ripen fruit due to the lack of an appropriate frost free season. Conversely, trees planted in the shade of north and east sides of structures may have slightly delayed blooming and ripening due to decreased heat exposure from the sun.
Another situation to watch for is zones at slightly lower elevation where cold air may be trapped. These spots may experience earlier frost and be colder than other areas. This is not the place to grow a variety that is marginally hardy or that may not regularly ripen due to the shortness of the growing season.
For the full text of this fact sheet and the list of suitable apples for Utah, go to http://extension.usu.edu/files/publications/publication/Horticulture\_Fruit\_2012\_01pr.pdf
Written by: Taun Beddes USU Extension Cache County Horticulture Agent