When is pollen worst in Fort Collins?

Fort Collins runs the classic three-wave calendar: tree pollen Mar–May, grass May–Jul, then ragweed Aug–Oct. The two worst stretches are the spring tree peak and the late-summer ragweed peak. Currently, ragweed pollen is what's driving counts this month.

What's in the air in Fort Collins right now?

In August, ragweed pollen is in season in Fort Collins — the dominant allergen you're likely reacting to right now. A live count, when available, confirms the day's actual reading; this reflects the typical peak windows for Fort Collins's high-elevation Mountain West climate.

Is tree or grass pollen higher in Fort Collins in spring?

In spring, tree pollen leads in Fort Collins — trees pollinate Mar–May, ahead of grass (May–Jul). The handoff is the tail of the tree window: tree counts taper as grass climbs, so an early-spring flare is more likely tree pollen and a late-spring one more likely grass.

What makes Fort Collins's pollen season distinctive?

Fort Collins sits in the high-elevation Mountain West zone, which means short, sharp seasons set late by elevation, with sagebrush adding to the late-summer weed load. That shapes when symptoms hit and which allergen to watch.

How do I reduce pollen exposure in Fort Collins?

Through Fort Collins's peak windows (tree Mar–May, grass May–Jul, ragweed Aug–Oct), keep windows shut and run AC on recirculate; counts run highest on dry, warm, windy mornings, so push outdoor activity to late afternoon or just after rain, which clears pollen from the air. A HEPA purifier indoors, a saline rinse after being outside, showering before bed, and starting antihistamines a week or two before your worst local window all measurably cut symptoms.

What pollen index counts as high?

Pollen is reported on a categorical scale — None, Low, Moderate, High, and Very High. "High" and above means most allergy sufferers notice symptoms even with brief outdoor exposure, and sensitized people should limit time outside and pre-medicate. "Low" to "Moderate" usually only affects highly sensitive individuals.

What is the allergy forecast in Fort Collins today?

The allergy forecast is the airborne-pollen outlook that drives hay fever — exactly what this page tracks. Today's pollen level for Fort Collins is shown above, broken into the tree, grass, and ragweed pollen behind most seasonal allergies. When the reading is High or Very High, plan for symptoms and pre-medicate; the seasonal calendar below shows which allergen leads in each part of the year.

Fort Collins, Colorado Pollen Count & Allergy Forecast

Fort Collins pollen count and allergy forecast — tree, grass, and ragweed seasons and what’s pollinating now

Fort Collins, CO · Pollen season

In August, ragweed pollen is in season in Fort Collins — the dominant allergen you're likely reacting to right now.

Based on the seasonal pollen calendar for this region.

Fort Collins on the WeatherStory Allergy Index

Fort Collins isn't one of the 100 metros on the WeatherStory Allergy Index, but the nearest ranked metro — Denver, CO, about 55 miles away — sits at #95 with a 244-day combined pollen season.

#95of 100nearest ranked metro

Load index: 27
Combined season: 244 days
Heaviest load: Tree · 91 days
Nearest ranked metro: Denver, CO · ~55 mi

See the full 100 worst U.S. cities for pollen — a modeled seasonal load ranking (see methodology).

Typical now — Augustseasonal estimate, not a live reading

Ragweed pollen typically leads in Fort Collins this time of year, at an estimated Moderate level. No live count is wired up; this reflects the seasonal calendar.

Pollen by type this season

TreeOut of seasonpeaks Mar–May
GrassOut of seasonpeaks May–Jul
Weed / RagweedIn seasonpeaks Aug–Oct

What pollinates near Fort Collins

The tree, grass, and weed species that drive Fort Collins’s pollen seasons, with each plant’s typical peak.

Trees

Juniper Juniperuspeaks March–April
Cottonwood Populuspeaks March–April
Aspen Populus tremuloidespeaks April–May
Ponderosa pine Pinus ponderosapeaks May–June
Box elder Acer negundopeaks March–April

Grasses

Kentucky bluegrass Poa pratensispeaks May–July
Smooth brome Bromus inermispeaks May–July
Timothy Phleum pratensepeaks June–July
Orchard grass Dactylis glomeratapeaks June–July

Weeds

Sagebrush Artemisia tridentatapeaks August–September
Common ragweed Ambrosia artemisiifoliapeaks August–September
Russian thistle Salsola traguspeaks August–September
Kochia Bassia scopariapeaks August–September

Species are the region’s common wind-pollinated plants; peak months are a seasonal estimate, not a measured count — see methodology.

Fort Collins’s allergy year

Typical month-by-month pollen intensity for Fort Collins, tuned to its latitude and climate region — darker means higher typical counts. The highlighted column is the current month.

JFMAMJJASOND

TreeMar–Jun

GrassMay–Aug

RagweedAug–Oct

How Fort Collins compares to the U.S. average

Each colored bar is Fort Collins’s typical season against the national-average window (grey). The offset is the per-city timing shift.

Treeabout average

Grassabout average

Ragweedabout average

“U.S. average” is the textbook tree Mar–May, grass May–Jul, ragweed Aug–Oct calendar. The shift is a phenology estimate (Hopkins’ bioclimatic law), not a measured count — see methodology.

How Fort Collins’s pollen count works

The calendar above is tuned to Fort Collins’s high-elevation Mountain West climate, not a national average: tree pollen runs from week 10 (early March) to week 23 (early June), grass from week 18 (early May) to week 31 (early August), and ragweed from week 31 (early August) to week 40 (early October) here — a 244-day combined pollen season. Those windows are why ragweed pollen is the one in season in Fort Collins right now.

No live count is wired up for Fort Collins today, so the seasonal calendar above is your guide to which allergen is in season. Counts run highest on warm, dry, windy mornings and drop after rain, which washes pollen out of the air — reported on the None / Low / Moderate / High / Very High scale.

Frequently asked

When is pollen worst in Fort Collins?: Fort Collins runs the classic three-wave calendar: tree pollen Mar–May, grass May–Jul, then ragweed Aug–Oct. The two worst stretches are the spring tree peak and the late-summer ragweed peak. Currently, ragweed pollen is what's driving counts this month.
What's in the air in Fort Collins right now?: In August, ragweed pollen is in season in Fort Collins — the dominant allergen you're likely reacting to right now. A live count, when available, confirms the day's actual reading; this reflects the typical peak windows for Fort Collins's high-elevation Mountain West climate.
Is tree or grass pollen higher in Fort Collins in spring?: In spring, tree pollen leads in Fort Collins — trees pollinate Mar–May, ahead of grass (May–Jul). The handoff is the tail of the tree window: tree counts taper as grass climbs, so an early-spring flare is more likely tree pollen and a late-spring one more likely grass.
What makes Fort Collins's pollen season distinctive?: Fort Collins sits in the high-elevation Mountain West zone, which means short, sharp seasons set late by elevation, with sagebrush adding to the late-summer weed load. That shapes when symptoms hit and which allergen to watch.
How do I reduce pollen exposure in Fort Collins?: Through Fort Collins's peak windows (tree Mar–May, grass May–Jul, ragweed Aug–Oct), keep windows shut and run AC on recirculate; counts run highest on dry, warm, windy mornings, so push outdoor activity to late afternoon or just after rain, which clears pollen from the air. A HEPA purifier indoors, a saline rinse after being outside, showering before bed, and starting antihistamines a week or two before your worst local window all measurably cut symptoms.
What pollen index counts as high?: Pollen is reported on a categorical scale — None, Low, Moderate, High, and Very High. "High" and above means most allergy sufferers notice symptoms even with brief outdoor exposure, and sensitized people should limit time outside and pre-medicate. "Low" to "Moderate" usually only affects highly sensitive individuals.
What is the allergy forecast in Fort Collins today?: The allergy forecast is the airborne-pollen outlook that drives hay fever — exactly what this page tracks. Today's pollen level for Fort Collins is shown above, broken into the tree, grass, and ragweed pollen behind most seasonal allergies. When the reading is High or Very High, plan for symptoms and pre-medicate; the seasonal calendar below shows which allergen leads in each part of the year.

Pollen & allergy guides

For the science behind Fort Collins’s pollen seasons — how counts are measured, when each type peaks, and what the numbers mean — see the pollen & allergy guides.

More for Fort Collins

See the full Fort Collins, CO weather forecast — hour-by-hour outlook, NOAA radar, satellite, and air quality.