When is pollen worst in Boulder?

Boulder 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, grass pollen is what's driving counts this month.

What's in the air in Boulder right now?

In June, grass pollen is in season in Boulder — 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 Boulder's high-elevation Mountain West climate.

Is tree or grass pollen higher in Boulder in spring?

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

Boulder 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 Boulder?

Through Boulder'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.

Boulder, Colorado Pollen Count

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

Boulder, CO · Pollen season

In June, grass pollen is in season in Boulder — the dominant allergen you're likely reacting to right now.

Based on the seasonal pollen calendar for this region.

Pollen by type this season

TreeOut of seasonpeaks Mar–May
GrassIn seasonpeaks May–Jul
Weed / RagweedOut of seasonpeaks Aug–Oct

Boulder pollen calendar

Typical peak months for each pollen type in this climate region. The highlighted column is the current month.

JFMAMJJASOND

TreeMar–May

GrassMay–Jul

WeedAug–Oct

How Boulder’s pollen count works

The calendar above is tuned to Boulder’s high-elevation Mountain West climate, not a national average: tree pollen peaks Mar–May, grass May–Jul, and ragweed Aug–Oct here. Those windows are why grass pollen is the one in season in Boulder right now.

No live count is wired up for Boulder 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 Boulder?: Boulder 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, grass pollen is what's driving counts this month.
What's in the air in Boulder right now?: In June, grass pollen is in season in Boulder — 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 Boulder's high-elevation Mountain West climate.
Is tree or grass pollen higher in Boulder in spring?: In spring, tree pollen leads in Boulder — 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 Boulder's pollen season distinctive?: Boulder 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 Boulder?: Through Boulder'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.

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

Pollen by type this season

Boulder pollen calendar

How Boulder’s pollen count works

Frequently asked

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