When is pollen worst in Indianapolis?

The late-summer ragweed run is the headline in Indianapolis: weed pollen peaks Aug–Nov, the longest and most punishing window of the year here. Tree pollen comes first (Mar–May) and grass bridges the gap (May–Oct), but it's the ragweed stretch that floors most sufferers. Currently, grass and ragweed pollen are in season.

What's in the air in Indianapolis right now?

In September, grass and ragweed pollen are in season in Indianapolis — grass peaks May–Oct and ragweed peaks Aug–Nov. On Indianapolis's warm, humid subtropical Southeast calendar the typical September level is High, led by ragweed pollen — a seasonal estimate, not a live count.

Is tree or grass pollen higher in Indianapolis in spring?

In spring, tree pollen leads in Indianapolis — trees pollinate Mar–May, ahead of grass (May–Oct). 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 Indianapolis's pollen season distinctive?

Indianapolis sits in the warm, humid subtropical Southeast zone, which means an unusually long, overlapping season — the warm climate stretches grass across much of the year and pushes ragweed deep into autumn. That shapes when symptoms hit and which allergen to watch.

How do I reduce pollen exposure in Indianapolis?

Through Indianapolis's peak windows (tree Mar–May, grass May–Oct, ragweed Aug–Nov), 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.

When does the next pollen season start in Indianapolis?

Tree pollen is next in Indianapolis: it opens around week 10 (early March), peaks around week 15, and runs about 91 days.

What is the allergy forecast in Indianapolis today?

With no live reading for Indianapolis today, its allergy forecast is the seasonal estimate above: a typical September level of High, led by ragweed pollen.

Indianapolis, Indiana Pollen Count & Allergy Forecast

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

Indianapolis, IN · Pollen season

In September, grass and ragweed pollen are in season in Indianapolis — grass peaks May–Oct and ragweed peaks Aug–Nov.

Based on the seasonal pollen calendar for this region.

Indianapolis on the WeatherStory Allergy Index

Indianapolis ranks #10 of 100 U.S. metros on the WeatherStory Allergy Index, with a modeled load index of 42 and a 274-day combined pollen season — its heaviest load is grass pollen, running 183 days.

#10of 100

Load index: 42
Combined season: 274 days
Heaviest load: Grass · 183 days

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

Typical now — Septemberseasonal estimate, not a live reading

Ragweed pollen typically leads in Indianapolis in September, at an estimated High level.

Pollen by type this season

TreeOut of seasonpeaks Mar–May
GrassIn seasonpeaks May–Oct
Weed / RagweedIn seasonpeaks Aug–Nov

What pollinates near Indianapolis

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

Trees

Oak Quercuspeaks March–April
Loblolly pine Pinus taedapeaks March–April
Pecan Carya illinoinensispeaks April–May
Sweetgum Liquidambar styracifluapeaks March–April
Mulberry Moruspeaks March–April
Elm Ulmuspeaks February–March

Grasses

Bermuda grass Cynodon dactylonpeaks May–September
Bahia grass Paspalum notatumpeaks May–September
Johnson grass Sorghum halepensepeaks June–August
Timothy Phleum pratensepeaks May–June

Weeds

Common ragweed Ambrosia artemisiifoliapeaks August–October
Giant ragweed Ambrosia trifidapeaks August–October
Pigweed Amaranthuspeaks August–September
English plantain Plantago lanceolatapeaks May–September

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

Indianapolis’s allergy year

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

JFMAMJJASOND

TreeMar–May

GrassMay–Oct

RagweedAug–Nov

How Indianapolis compares to the U.S. average

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

The calendar above is tuned to Indianapolis’s warm, humid subtropical Southeast climate, not a national average: tree pollen runs from week 10 (early March) to week 22 (late May), grass from week 18 (early May) to week 43 (late October), and ragweed from week 31 (early August) to week 48 (late November) here — a 274-day combined pollen season. Those windows are why grass and ragweed pollen are in season in Indianapolis right now.

No live count is wired up for Indianapolis today, so the seasonal calendar above is your guide to which allergen is in season.

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

Frequently asked

When is pollen worst in Indianapolis?: The late-summer ragweed run is the headline in Indianapolis: weed pollen peaks Aug–Nov, the longest and most punishing window of the year here. Tree pollen comes first (Mar–May) and grass bridges the gap (May–Oct), but it's the ragweed stretch that floors most sufferers. Currently, grass and ragweed pollen are in season.
What's in the air in Indianapolis right now?: In September, grass and ragweed pollen are in season in Indianapolis — grass peaks May–Oct and ragweed peaks Aug–Nov. On Indianapolis's warm, humid subtropical Southeast calendar the typical September level is High, led by ragweed pollen — a seasonal estimate, not a live count.
Is tree or grass pollen higher in Indianapolis in spring?: In spring, tree pollen leads in Indianapolis — trees pollinate Mar–May, ahead of grass (May–Oct). 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 Indianapolis's pollen season distinctive?: Indianapolis sits in the warm, humid subtropical Southeast zone, which means an unusually long, overlapping season — the warm climate stretches grass across much of the year and pushes ragweed deep into autumn. That shapes when symptoms hit and which allergen to watch.
How do I reduce pollen exposure in Indianapolis?: Through Indianapolis's peak windows (tree Mar–May, grass May–Oct, ragweed Aug–Nov), 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.
When does the next pollen season start in Indianapolis?: Tree pollen is next in Indianapolis: it opens around week 10 (early March), peaks around week 15, and runs about 91 days.
What is the allergy forecast in Indianapolis today?: With no live reading for Indianapolis today, its allergy forecast is the seasonal estimate above: a typical September level of High, led by ragweed pollen.