Last Frost Date: When Is It Time To Plant A Garden In Boulder?

BOULDER, CO — Inflation, the rising cost of food and the nutritional benefits of homegrown produce have cultivated a new crop of home gardeners in Boulder.

Whether you’re a first-time or experienced gardener, one of the most important dates you need to know as you think about your garden this spring is the last frost.

The danger of frost in Boulder passes on May 9, according to The Old Farmer’s Almanac, which offers a ZIP code tool to help gardeners figure out when to plant what.

The growing season is 144 days long in Boulder. Looking ahead to fall, the first frost usually occurs around Oct. 1.

According to the publication, there’s a 30 percent probability of a frost occurring after May 9, as the date is determined using National Oceanic and Atmospheric historical data from 1981-2010, and is not “set in stone,” The Old Farmer’s Almanac said.

May 9 represents the average date of the final “light freeze,” which occurs when the temperature dips between 29 and 32 degrees Fahrenheit. At that temperature, tender plants can be killed.

A “moderate freeze,” between 25 and 28 degrees, is destructive to most plants; and a “severe freeze,” at anything under 24 degrees, can do heavy damage to most garden plants, according to the almanac.

As the pandemic’s third gardening season gets underway in Boulder, The Old Farmer's Almanac has another tool to help gardeners decide when to plant which crops.

In Boulder, it’s usually best to start seeds outdoors for corn on May 9, potatoes on May 2 and spinach on March 28.

Here’s a look at other crops, and when the Old Farmer’s Almanac says to begin planting them in Boulder.

• Basil, May 9
• Bell Peppers, May 16
• Cabbage, April 11
• Celery, May 16
• Lettuce, April 25
• Sweet Potatoes, May 23
• Tomatoes, May 16
• Zucchini, May 23

Even before the pandemic, mental health experts pointed to gardening as a way to deal with stress.

Gardening provides physical exercise and promotes healthier eating, but it can also reduce worry among people who consider themselves perfectionists, psychologist Seth Gillihan said.

“Given the lack of control we have, gardening can be a good antidote for perfectionism,” Gillihan wrote in a 2019 Psychology Today blog. “No matter how carefully you plan and execute your garden, there are countless factors you can't predict — invasions by bugs, inclement weather, hungry rodents.”

With so many things out of their control, perfectionism is a waste of time, he said, so gardeners may ask themselves “why bother” trying to be perfect.