Ask a Specialist: When are the last-freeze dates in Utah?

USU Media Relations occassionally provides “ask the expert” type questions. This week, the question is “Do you have information on last-freeze dates in Utah?” The answer comes from Taun Beddes, Utah State University Cooperative Extension horticulturist: Determining when to plant a garden can be somewhat confusing in Utah’s unpredictable, varied climate where last-frost dates can vary by many days within just a few miles. Many experienced gardeners have planted at one point and later lost the plants to frost. An example of how fickle Utah’s climate can be is in Cache Valley. Frost-free days vary from an average of 113 days in Lewiston and Trenton to 158 days on the USU campus. Similar examples occur across the state. Although exact last-frost dates are not available for all areas, a person can still determine when to plant. Often, the best thing to do is chat with a local farmer or experienced gardener in your area to determine what works for them. Other factors to consider include geographic characteristics of where you live. When a yard is located in a populated area or on a mountain bench, it usually has a longer growing season. Other areas located at slightly lower elevations, where cold air drains and cannot escape, have a shorter season due to the increased cold air. This is why local commercial orchards are generally located on benches. Additionally, urban and suburban areas are slightly warmer than surrounding areas due to the urban heat effect. Heat from buildings and warmth generated by sunlight reflected from roads and other surfaces increase temperatures and delay frost. In addition to knowing frost information, a wise gardener takes into account the needs of the plants. Vegetables planted locally fall into four basic categories: hardy, semi-hardy, tender and very tender. Depending on which category a plant belongs to, planting dates vary from early spring until early summer. Consider the following: * Hardy vegetables, including asparagus, broccoli, cabbage, onions, peas and spinach, can be planted as soon as the soil is workable in early spring. This usually ranges between 45 and 60 days before the average last frost. These same vegetables can be safely planted until the date of the average last frost. * Semi-hardy plants, such as beets, carrots, lettuce and potatoes, can be planted one to two weeks after the hardy group. These can be planted until the average last-frost date. * Tender vegetables, such as celery, cucumbers, corn and most beans, should be planted on the average last-frost date in your area. * Very tender plants, such as squash, beans, melons, tomatoes, eggplants and peppers, should not be planted until at least a week after the average last frost has passed. Even if frost does not occur before this time, these plants will not grow well and are more susceptible to disease until warmer weather. If you have lost plants to frost, you are not alone. It is often due to Utah’s fickle weather, and all we can do is try again. For more information on fruit and vegetable gardening, visit the USU Extension website at: http://extension.usu.edu/yardandgarden/htm/vegetables-fruits-herbs. In Logan, the last freeze day is typically May 14, with the first freeze on Sept. 25, giving the area 135 frost-free days.

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