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Alaska Pollen Calendar: Season by Species

Birch runs April 20 to June 30. Below: every tracked species, its months, and who published them.

Birch pollen typically runs April 20 to June 30 here. In October, the calendar has none of the tracked species in season.
Birch season
Apr 20 to Jun 30
In season this October
0
Sourced windows
4

Where the Alaska pollen year stands

Climatological windows, resolved against today
quiet
groups in season, mid October
no tracked species in window
Apr 20 to Jun 30
birch season
per State of Alaska Epidemiology Bulletin No. 10 (2017), Dept. of Health and Social Services
September 5
median first frost
the date that ends ragweed season here (derived)

The State of Alaska Epidemiology Bulletin states that in Alaska pollen season typically occurs during May through August, and that Anchorage and Fairbanks reported some of the highest tree pollen counts in the world in 2014 and 2016.

The calendar

What pollinates when in Alaska

Every bar is a sourced season window; the institution and sentence behind each one are printed in the species cards below. Bars marked ❄ end at Alaska’s median first frost, a date we compute from NOAA normals rather than copy from a source, because frost is what physically stops frost-tender weeds like ragweed.

BirchTreeApril 20 to June 30
AlderTreeApril 20 to June 30
GrassesGrassMay 20 to July 31
Weeds (mixed)WeedJune 1 to August 31
trees grasses weeds today❄ end derived from median first frost

Windows are climatological typicals for Alaska as published by the sources on this page. They say when a season normally runs, not how strong any given day is.

Orchard grass flower heads with pink anthers spread for wind pollination
The species that leads a state’s calendar decides when its worst weeks land, which is why every state page opens with different months. “Dactylis glomerata - Pink with pollen” by Bob Harvey, CC BY-SA 2.0
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Species by species

The windows, with their sources

Each card shows the months, the institution that published them, and the verbatim sentence the window came from. Where a date is computed by us rather than published, the card says so in as many words.

BirchTree

Betula spp.

April 20 to June 30

The source puts the peak around May 15.

“In 2015, birch, alder, cottonwood, spruce, and willow pollen counts were highest in late April-June; grass pollen counts were highest from late May-July; weed pollen counts were highest during June-August; and outdoor mold spore counts were highest during late July-September.”

State of Alaska Epidemiology Bulletin No. 10 (2017), Dept. of Health and Social Services

Peak sourced from University of Alaska Fairbanks Geophysical Institute, which states verbatim: birch trees typically shed large amounts of pollen May 10th through the 20th. The bulletin notes Anchorage and Fairbanks reported some of the highest tree pollen counts in the world in 2014 and 2016.

What the allergy bodies say, in their words. AAAAI: “Seasonal allergic rhinitis is often caused by tree pollen in the early spring. During the late spring and early summer, grass pollen often cause symptoms. Late summer and fall hay fever is caused by weed pollen.” ACAAI: “Tree pollination begins earliest in the year followed by grass pollination later in the spring and summer and ragweed in the late summer and fall.” For anything about symptoms or treatment, see a clinician.

The frost connection

Why ragweed season in Alaska ends on a frost date

Ragweed is a short-day annual: it starts shedding pollen as days shorten in late summer and keeps going until cold kills it. The US EPA’s technical documentation for its ragweed pollen indicator puts it plainly: the season “ends in response to cold weather in the fall (i.e., first frost)”, and ragweed “will not continue flowering once temperatures dip below freezing.” EPA’s own analysis truncates every station’s ragweed season at the first fall frost.

Alaska's calendar above carries no frost-derived weed bar: its sources either publish the weed season's own dates or do not make ragweed the state's fall story. The state's median first frost, September 5, still marks where any frost-tender weed season would close.

Common ragweed flower spike held upright against a clear blue sky
Common ragweed in flower. Each spike sheds wind-borne pollen from late summer until the plant is killed by freezing temperatures, which is why the end of its season is a frost statistic rather than a botany fact. “Ambrosia artemisiifolia flowerhead7” by Harry Rose, CC BY 2.0
Live proxy · USA-NPN

Is tree season running early or late in Alaska?

USA-NPN’s Extended Spring Indices measure how early or late spring leaf-out and bloom are running against the 1991 to 2020 normal. The index knows nothing about pollen; it tracks cloned lilacs and honeysuckles. But wind-pollinated trees flower in the same early-spring window it measures, so it is a usable, clearly labelled proxy for whether Alaska’s tree pollen season is ahead of or behind schedule this year.

No Spring Index reading for Alaska. USA-NPN’s Extended Spring Indices anomaly grids cover the conterminous United States only, so there is no early-or-late measurement to show here. The sourced calendar above is unaffected.

Pine branch with yellow pollen cones releasing a visible cloud of pollen into the wind
A pine shedding pollen into the wind. Wind-pollinated trees release enormous quantities because almost none of it lands on another flower, which is also why it lands on everything else. “Pine releasing pollen into the wind in Tuntorp 1” by W.carter, CC BY-SA 4.0
How this page is built

A calendar, not a count

Sourced windows

Every season window names the extension service, agency or university that published it, with the sentence quoted on the card. Where nobody publishes a window, the page says so instead of inventing one.

Derived ragweed ends

Weed bars marked with the frost symbol end on the state’s median first frost, computed from NOAA 1991 to 2020 normals and labelled as derived, on the strength of EPA’s ragweed indicator documentation.

A labelled proxy, not a forecast

The Spring Index anomaly is a measurement of the spring that has already run. It shifts nothing except spring tree windows, and only while the year’s spring is actually in progress.

No counts, by design

Daily counts belong to the certified counting stations of the National Allergy Bureau, and search engines already print them. This site publishes the part nobody prints: the calendar.

Common questions

Alaska pollen season FAQ

Orchard grass flower heads with pink anthers spread for wind pollination
Orchard grass in flower, anthers out. Grass pollen is the midsummer act of the calendar almost everywhere, and a lawn kept mowed never reaches this stage, which is the whole connection to the mowing schedule. “Dactylis glomerata - Pink with pollen” by Bob Harvey, CC BY-SA 2.0
The rest of the Alaska calendar

Plan around the Alaska seasons

Alaska frost datesThe median first frost is the date that ends ragweed season here. Same number, two pages.Spring bloom timingThe same Spring Index that flags an early tree pollen year also moves the wildflower calendar.Alaska lawn calendarGrass pollen comes from grass allowed to flower. The mowing calendar is the other half of that story.

More West pollen calendars

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Season windows are climatological typicals, each attributed on its card to the institution that published it, with the supporting sentence quoted. Frost-derived weed season ends are computed by us from NOAA 1991 to 2020 median first frost dates and labelled as derived wherever they appear; the frost link is documented by the US EPA’s ragweed pollen indicator technical documentation. Spring Index anomalies are read live in your browser from the USA National Phenology Network (www.usanpn.org, CC BY 4.0) and shown as a labelled proxy for spring tree pollen timing. National picture: every state’s pollen calendar →
Hero image: “Dactylis glomerata - Pink with pollen” by Bob Harvey, CC BY-SA 2.0