Fort Collins, CO Frost Dates
Published: February 1, 2026 · Updated: April 23, 2026
USDA Zone 6a
Last Spring Frost
March 30
Safe to transplant after this date
First Fall Frost
November 1
Protect tender plants before this date
Frost-Free Season
216 days
Late March to Mid-November
303 days until last frost in Fort Collins — March 30
Fort Collins’s zone 6a climate provides a generous 216-day frost-free window — long enough for a wide variety of vegetables and excellent conditions for both cool-season and warm-season lawn grasses.
Complete Planting Calendar for Fort Collins
Lawn Care Timing for Fort Collins
Based on Fort Collins's USDA zone 6a frost dates: The last frost of March 30 marks when warm-season grasses begin recovering. Apply spring fertilizer in Late March when soil reaches 55°F. The first fall frost of November 1 sets your deadlines — complete overseeding by September 1–October 1 and apply winterizer by Mid-November.
USDA Zone 6a Summary
Seven months frost-free. Transition zone between cool-season and warm-season grasses. Mid-Atlantic states.
Frequently Asked Questions
What is the last frost date in Fort Collins, CO?
The average last spring frost in Fort Collins is March 30. This is based on USDA zone 6a historical averages. Plan transplanting and spring lawn care around this date — wait 2 weeks after for frost-sensitive plantings.
When is the first fall frost in Fort Collins?
Fort Collins’s average first fall frost is November 1. This sets deadlines for fall overseeding (must be done 6 weeks before) and winterizer application (by Mid-November).
When should I plant tomatoes in Fort Collins?
Transplant tomato seedlings outdoors after March 30. Start seeds indoors Late January. Direct sow warm-season crops after april 7.
When should I overseed my lawn in Fort Collins?
The prime overseeding window in Fort Collins is September 1–October 1. This ensures warm soil for germination before the first fall frost on November 1.
When should I apply winterizer in Fort Collins?
Apply winterizer fertilizer in Fort Collins by Mid-November. This high-potassium application hardens grass cell walls before freeze damage. Your first fall frost of November 1 is the hard deadline.