Use this planting calendar to find the best times of the year to grow fruits, vegetables, herbs, flowers, and other popular plants in Thornton, CO, based on the USDA Hardiness Zone 5b.
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Thornton, CO Frost Dates & Growing Season
Last Spring Frost Date for Thornton, CO
The average last frost date in spring for Thornton is May 7th. For gardeners planting sensitive crops like tomatoes, peppers, and basil, it is generally recommended to wait until May 21st before moving plants outdoors. Waiting these extra few weeks significantly reduces the risk of a late freeze damaging young transplants.
First Fall Frost Date for Thornton, CO
The average first frost date in fall for Thornton is October 4th. This date marks the approximate end of the growing season for tender plants. Gardeners should plan to harvest frost-sensitive vegetables or provide heavy protection (such as row covers) before this date to avoid crop loss.
Growing Season Length in Thornton, CO
Based on historical frost data, the estimated growing season length in Thornton is approximately 150 days. This duration determines which vegetable varieties have enough time to reach maturity before the winter cold sets in. Short-season varieties are recommended for crops that require a longer warm period.
Please note: These dates are climatological averages. Actual weather conditions vary by year. Always check the local 10-day forecast before planting.
Thornton, CO Planting Calendar
This weekly planting calendar displays the ideal windows for starting seeds, transplanting, and harvesting your plants.
Thornton, CO Monthly Planting Recommendations
February
In February, recommended activities include starting Petunia seeds indoors (from February 26th to March 12th), starting Pansy seeds indoors (from February 26th to March 12th), and starting Begonia seeds indoors (from February 26th to March 12th).
March
In March, recommended activities include starting Tomato seeds indoors (from March 12th to March 26th), starting Black Eyed Susan seeds indoors (from March 12th to March 26th), and starting Cauliflower seeds indoors (from March 12th to March 26th).
April
In April, recommended activities include direct sowing Mustard (from April 9th to April 23rd), direct sowing Poppy (from April 9th to April 23rd), and direct sowing Hyssop (from April 23rd to May 7th).
May
In May, recommended activities include direct sowing Lemon Balm (from May 7th to May 21st), direct sowing Chia (from May 21st to June 4th), and direct sowing Cucumber (from May 14th to May 28th).