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Last Spring Frosts

By Carl Wilson, Horticulturist, Denver Cooperative Extension

Last spring frost dates are important to home gardeners in order to plan when to set out frost-sensitive annuals, vegetables and even tropical container plants.

Sometimes different frost dates are quoted for our area. The difference is a statistical one in the degree of confidence in the date. This risk factor also presents a choice for home gardeners. How much of a chance are you willing to take in placing a tender plant outdoors?

For example, in Denver the last spring frost date at a 50% confidence level is May 2nd. This computes to a growing season of 157 days. If you want to be 80% confident frosts are past, it's May 12th. If you're not a risk taker and want to be 90% confident, wait until May 18th to plant. All dates are based on 47 years of data. The latest Denver frost date? June 2nd in 1951.

Frost dates are available for hundreds of Colorado cities on the CSU Atmospheric Sciences web site at:

Log on to check the information for your location and make your planting decisions based on your own risk tolerance.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010