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Grass Pollen Count

Summer Season, Symptoms & High-Count Areas

What Is the Grass Pollen Count?

Grass pollen count peaks in late spring and early summer across the US, affecting over 40 million people. The Willamette Valley in Oregon is one of the highest grass pollen regions in the world.

Peak season: May through August, peaking late May to July

Most affected regions: Pacific Northwest, Midwest, Southeast

Common symptoms: Sneezing, runny nose, itchy eyes, asthma flares.

Tips for High Grass Pollen Count Days
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Mow Less During Season
Mowing sends grass pollen airborne. If possible, have someone else mow during peak season, or wear a mask.
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Avoid Grass After Mowing
Freshly cut grass releases pollen at high concentrations. Wait at least an hour after mowing before going outside.
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Keep Indoor Air Clean
Close windows on high-count days. HEPA air purifiers help reduce indoor grass pollen significantly.
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Rain Helps Temporarily
Rain washes grass pollen from the air, but moist conditions after rain can also elevate mold spores.
Check Grass Pollen Count by City
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Frequently Asked Questions

What is a high grass pollen count?

Grass pollen counts above 20 grains per cubic meter are considered high for sensitive individuals. Oregon's Willamette Valley regularly sees counts above 500 during peak season.

When is grass pollen season?

Grass pollen season runs May through August in most of the US, peaking in late May and June. In warm southern states, grass can pollinate from March through September.

Which grasses cause allergies?

Timothy, Bermuda, Kentucky bluegrass, orchard grass, and ryegrass are the most allergenic grasses in the US. Bermuda is especially problematic in the South due to its long growing season.