Gardening in Utah

Hardiness zones in Utah

USDA hardiness zones measure one thing: the average coldest temperature your area reaches in a typical winter. They do not describe summer heat, rainfall, or soil type. Utah spans a wide range, from zone 4a up to zone 8b. That is one of the broadest spreads of any state, built from data at 137 weather stations across Utah. A lower zone number means colder winters and a shorter list of plants that survive outdoors year round. Zone 4a areas see winter lows far colder than zone 8b areas. Between those two ends, Utah also includes zones 5a, 5b, 6a, 6b, 7a, 7b, and 8a. Each jump of one zone number, like 5a to 5b, marks a 5 °F (2.8 °C) step in typical winter lows. Check your own zone before you choose perennials, shrubs, or trees meant to stay in the ground through winter. A plant rated for zone 7 may not survive a zone 5 winter in northern or high-elevation parts of the state.

• Zone 4a
• Zone 5a
• Zone 5b
• Zone 6a
• Zone 6b
• Zone 7a
• Zone 7b
• Zone 8a
• Zone 8b

Frost dates

Your last frost date marks the point in spring when the cold is statistically done for the season. Across Utah, that date ranges from as early as March 14 in the mildest spots to as late as June 21 in the coldest ones. The fall side works the same way in reverse. The first frost of autumn can arrive as early as September 1 or hold off until November 10, depending on where you garden in the state. That spread of nearly three months on each end comes from real differences in elevation and location across Utah's 137 weather stations. A garden near Utah's warmest valleys plants and harvests on a very different calendar than one at high elevation. Treat these dates as averages, not guarantees. A frost can still strike a week or two on either side of the typical date in any given year. Use your own local frost dates, not a single statewide date, to decide when to plant tender vegetables or move houseplants outdoors for summer. Gardeners near the early end of the range get a much longer stretch between frosts than those near the late end.

Climate

Utah's climate is not one climate. The state's hardiness zones run from 4a to 8b, a spread of nine steps that covers nearly the full range the USDA chart uses. That alone tells you winter cold varies enormously from one part of Utah to another. The growing season length shows the same pattern. Data from 137 weather stations across the state shows typical frost-free seasons as short as 51 days in some locations and as long as 239 days in others. A 51-day season barely fits a single fast crop between frosts. A 239-day season supports multiple plantings and many slower-growing crops in the same year. These numbers come from averages at each station, not from a single statewide figure, which is why the range is so wide. Zone numbers and frost dates describe winter cold and the length of the frost-free period only. They say nothing about summer heat, rainfall, humidity, or soil. A full zone 7 reading in one part of Utah does not guarantee the same summer conditions as a zone 7 reading elsewhere. Look up the figures for your own station, or the nearest one to you, rather than relying on a single number for the whole state. That local figure is the one that matches what happens in your own yard.

Season length

Growing season length counts the days between your last spring frost and your first fall frost. In Utah, that count ranges from 51 days up to 239 days, depending on where in the state a garden sits. A short, 51-day season favors fast crops like radishes, lettuce, and other quick greens over anything that needs a long stretch of warm weather. A long, 239-day season leaves room for crops that take all summer to mature, plus a second round of a faster one. Check the season length for your own area rather than assuming the statewide range applies to your yard. Your local frost dates, not the state's extremes, set the real start and end of your season.