When is pollen worst in Denver?

Denver 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 Denver right now?

In August, ragweed pollen is in season in Denver — 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 Denver's high-elevation Mountain West climate.

Is tree or grass pollen higher in Denver in spring?

In spring, tree pollen leads in Denver — 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 Denver's pollen season distinctive?

Denver 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 Denver?

Through Denver'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 Denver today?

The allergy forecast is the airborne-pollen outlook that drives hay fever — exactly what this page tracks. Today's pollen level for Denver 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.

Denver, Colorado Pollen Count & Allergy Forecast

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

Denver, CO · Pollen season

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

Based on the seasonal pollen calendar for this region.

Denver on the WeatherStory Allergy Index

Denver ranks #95 of 100 U.S. metros on the WeatherStory Allergy Index, with a modeled load index of 27 and a 244-day combined pollen season — its heaviest load is tree pollen, running 91 days.

#95of 100

Load index: 27
Combined season: 244 days
Heaviest load: Tree · 91 days

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 Denver 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 Denver

The tree, grass, and weed species that drive Denver’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.

Denver’s allergy year

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

JFMAMJJASOND

TreeMar–May

GrassMay–Jul

RagweedAug–Oct

How Denver compares to the U.S. average

Each colored bar is Denver’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 Denver’s pollen count works

The calendar above is tuned to Denver’s high-elevation Mountain West climate, not a national average: tree pollen runs from week 10 (early March) to week 18 (early May), grass from week 18 (early May) to week 27 (early July), 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 Denver right now.

No live count is wired up for Denver 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 Denver?: Denver 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 Denver right now?: In August, ragweed pollen is in season in Denver — 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 Denver's high-elevation Mountain West climate.
Is tree or grass pollen higher in Denver in spring?: In spring, tree pollen leads in Denver — 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 Denver's pollen season distinctive?: Denver 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 Denver?: Through Denver'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 Denver today?: The allergy forecast is the airborne-pollen outlook that drives hay fever — exactly what this page tracks. Today's pollen level for Denver 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 Denver’s pollen seasons — how counts are measured, when each type peaks, and what the numbers mean — see the pollen & allergy guides.

More for Denver

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