Is it allergy season in Idaho?

Idaho's diverse geography produces one of the West's more complex multi-wave allergy seasons. The Treasure Valley around Boise sees juniper and mountain cedar begin in late February to March, followed by cottonwood along the rivers in April. The Snake River Plain's agricultural flatlands drive heavy grass pollen from May through August — similar in intensity to Oregon's Willamette Valley but covering the vast Eastern Idaho plain. The fall season is defined by sagebrush (Artemisia) — the state's dominant weed pollen — which peaks August through October across the high desert. Eastern Idaho cities like Idaho Falls and Pocatello have shorter spring seasons but longer, more intense sagebrush falls.

The Treasure Valley around Boise has the longest and most diverse allergy season in the state. Eastern Idaho's high-elevation plain has a compressed spring but intense sagebrush fall. The Northern Panhandle shares Pacific Northwest weather patterns with Washington and has a birch-influenced spring. Mountain valleys get a delayed, compressed season from elevation.

Treasure Valley / Boise

The state's most populated allergy corridor

Boise, Nampa, and Meridian sit in the Snake River Plain where juniper begins in late February. Cottonwood follows along the Boise River in April. The valley's warm, dry summer drives intense grass pollen. Sagebrush peaks August–October as winds sweep in from the surrounding high desert.

Juniper · Feb–AprGrass · May–AugSagebrush · Aug–Oct

Eastern Idaho / Idaho Falls

High plain — intense sagebrush and grass season

Idaho Falls and Pocatello sit at higher elevation than Boise. The spring tree season is shorter and starts 3–4 weeks later. But the surrounding Snake River Plain agriculture produces heavy grass pollen in June and July. The sagebrush fall season is particularly pronounced due to the vast surrounding high desert.

Grass · Jun–AugSagebrush · Aug–Oct (intense)Compressed spring

Northern Panhandle / Coeur d'Alene

Pacific Northwest influence — birch and cedar

North Idaho shares climate patterns with eastern Washington. Birch becomes more prominent in the spring pollen mix here than anywhere else in Idaho. Grass is significant in summer, and ragweed makes a small appearance in fall — more than in southern Idaho. Rainfall moderates counts compared to the drier south.

Birch · Apr–MayGrass · Jun–AugSome ragweed in fall

Mountain Valleys / Sun Valley

Elevation compresses and delays the season

High-elevation mountain communities like Sun Valley and Stanley have a compressed, delayed allergy season. Tree pollen starts in May or June, grass peaks briefly in July, and sagebrush begins in August. Total season length is 4–5 months rather than the 7–8 months seen in the Treasure Valley.

Compressed May–Sep seasonGrass · JulSagebrush · Aug–Sep

Each row shows a full year of pollen for one region — trees in blue, grasses in green, weeds in amber. Look for where all three rows go quiet at the same time — that's your window.

Oral Allergy Syndrome (also called pollen-food allergy syndrome) causes tingling or mild itching in the mouth when you eat certain raw foods during the relevant pollen season. The proteins in the food are similar enough to the pollen protein that your immune system cross-reacts. Cooking usually deactivates the offending protein, so the same food cooked may cause no reaction.

Cottonwood & elm pollen

Stone fruits & apples

Apples, pears, peaches, cherries, plums, almonds, hazelnuts, carrots, celery

Peak risk April–May in the Treasure Valley. Cottonwood along the Boise River is one of the most visible spring events — the fluffy white seeds are seeds, not pollen, but the invisible pollen triggers reactions weeks before the seed release.

Grass pollen (orchard, timothy)

Tomatoes, potatoes & melons

Tomatoes, potatoes, kiwi, watermelon, cantaloupe, oranges (in some cases)

Peak risk May–August across the Snake River Plain. The agricultural core of Idaho produces some of the highest grass pollen counts in the Intermountain West. Seed crop grass fields in the Twin Falls area are particularly productive.

Sagebrush (Artemisia) pollen

Celery, carrots & spices

Celery, carrots, parsley, coriander, fennel, black pepper, sunflower seeds, honey

Peak risk August–October statewide. Sagebrush (Artemisia tridentata) is Idaho's dominant fall allergen and covers millions of acres of the state. The fall season can be intense across the entire southern plain.

Not medical advice. If you suspect OAS, speak with an allergist — it can sometimes progress, and symptoms that extend beyond the mouth should be evaluated.