Portland pollen forecast — Lan Su Chinese Garden neighborhood
Pollen Today
Today (20 September) pollen in Lan Su Chinese Garden, Portland is high; ragweed is high; grass is moderate; mugwort is low.
Pollen Tomorrow
Tomorrow (21 September 2026) grass declining, ragweed declining, mugwort no longer expected.
7-Day Trend
Over the next week mugwort and ragweed will increase; grass will decrease.
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Pollen Risk
Today - 20 September
| Pollen species | Level | Value |
|---|---|---|
| Alder (Alnus) | None | 0/100 |
| Birch (Betula) | None | 0/100 |
| Hazel (Corylus) | None | 0/100 |
| Cypress (Cupressaceae) | None | 0/100 |
| Grass (Poaceae) | Moderate | 35/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | Low | 15/100 |
| Ragweed (Ambrosia) | High | 59/100 |
Tomorrow - 21 September
| Pollen species | Level | Value | 7-Day Trend |
|---|---|---|---|
| Alder (Alnus) | None | 0/100 | — |
| Birch (Betula) | None | 0/100 | — |
| Hazel (Corylus) | None | 0/100 | — |
| Cypress (Cupressaceae) | None | 0/100 | — |
| Grass (Poaceae) | Low | 19/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | None | 0/100 | |
| Ragweed (Ambrosia) | Moderate | 43/100 |
Local Environmental Conditions
Lan Su Chinese Garden is a pacific Northwest city with Douglas fir, bigleaf maple, and hazels. Hazel and alder bloom in February — one of the earliest spring pollen triggers in the US. Tree season runs through May; grass follows through July.
Lan Su Chinese Garden, a landmark in Portland, opens its pollen season with alder and birch from February then maple builds through March and April. Peak grass pollen arrives in May and June, and plantain and nettle stretch the season into September. The damp, mild regional climate keeps pollen counts lower than in drier parts of the country, though spring rain events can trigger brief spikes, a defining feature of the local season.
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Frequently Asked Questions About Pollen in Oregon
Is pollen high in Portland right now?
On 20 September 2026, overall pollen levels in Portland are high. Ambrosia is the main contributor to airborne pollen, while grass and artemisia remain at lower levels
Will pollen levels change in Portland tomorrow?
On 21 September 2026, pollen conditions in Portland will be different from today, with ambrosia, grass continuing to decline
Is pollen expected to decrease in Portland this week?
According to the five-day outlook, grass pollen levels are expected to gradually decrease, while ambrosia and artemisia pollen will increase, suggesting mixed conditions later in the week.
Which pollen types are currently active in Portland?
On 20 September 2026, Ambrosia is the dominant pollen source in Portland. grass and artemisia are also present but at lower levels.
When is pollen season in Portland?
How often is the Portland pollen forecast updated?
The Portland pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Portland come from nearby or far away?
Studies show that most pollen exposure (often 70–90%) comes from nearby sources, such as local trees and vegetation. A good pollen forecast therefore depends on accurately representing local vegetation. Pollen can travel long distances, but this usually matters only early in the season or during specific wind events.
Are pollen levels in Portland based on measurements or forecasts?
Pollen data is often misunderstood. Most "pollen levels" are not real-time measurements, but forecasts.
Direct pollen measurements are typically delayed by 1-2 days because they require manual analysis. To show current conditions in Portland, modern forecasts combine recent measurements, weather data, and information about local vegetation.
This allows us to estimate pollen levels for today and the coming days, not just report the past.
Airmine’s atmospheric monitoring platform was developed with support from the European Space Agency (ESA)’s Business Applications and Space Solutions (BASS) team, using satellite and Earth observation technologies to improve emissions monitoring.
Understanding the Scale
The 0–100 scores represent risk levels, not direct measurements of pollen or air pollutant concentrations. Higher scores indicate higher risk. Pollen and air quality use different thresholds.
Pollen
| None | 0 | No or negligible risk of exposure. Pollen/mold exposure is expected to be minimal. |
| Low | 0-25 | Low risk of exposure. Small amounts of pollen or mold spores may be present. |
| Moderate | 25-50 | Moderate risk of exposure. Pollen/mold exposure is expected to be noticeable. |
| High | 50-75 | High risk of exposure. Elevated pollen/mold exposure is expected. |
| Very High | 75-100 | Very high risk of exposure. Pollen/mold exposure is expected to be at or near its highest levels. |
Get More in the Airmine Pollen app
Get 15-day pollen forecasts with morning, afternoon and evening detail, plus 5-day air quality forecasts. Explore interactive pollen risk maps, estimated pollen season start, route profiles and a symptoms diary.
Features and forecast availability vary by region. Currently covering Europe, the contiguous US, southern Canada, South Africa, Australia, Indonesia (Java & Bali), Brazil, Paraguay, Uruguay and the Buenos Aires area.
Developed with support from the European Space Agency (ESA) Business Applications and Space Solutions (BASS).
