Colorado pollen and allergy seasons
Colorado has a spring tree season along the Front Range and a strong late summer weed season led by ragweed and sagebrush.
Twelve month pollen calendar
What is active in September
Cities in Colorado
No tracked cities yet for Colorado.
Today and worst today come from live readings where available. Typical shows the usual level for this month from the seasonal profile.
Pollen is only half of what's in the air. See today's air quality in Colorado for ozone, dust, and smoke readings by city.
The Colorado allergy season
Allergy levels in Colorado peak in September, when ragweed pollen runs highest. The season moves through tree pollen around March, grass in June, weed pollen such as ragweed in September. Levels start to climb around March. The lowest pollen levels of the year arrive in January.
Common questions
When does allergy season start in Colorado?
Pollen levels in Colorado usually begin climbing in March and reach their highest point in September.
What is the worst month for allergies in Colorado?
September is typically the worst month in Colorado, driven by ragweed pollen.
When does ragweed season end in Colorado?
Ragweed pollen in Colorado usually fades by the end of October, after the first hard frost in colder areas.
When is the best time for allergies in Colorado?
January usually brings the lowest pollen levels of the year in Colorado.