Juniper runs April 1 to May 31. Below: every tracked species, its months, and who published them.
Juniper pollen typically runs April 1 to May 31 here. In October, the calendar has none of the tracked species in season.University of Utah research led by William Anderegg found that pollen seasons start 20 days earlier, are 10 days longer and feature 21% more pollen than they did in 1990 (source: https://science.utah.edu/news/allergy-season/, fetched 2026-08-27).
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 Utah’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.
Windows are climatological typicals for Utah as published by the sources on this page. They say when a season normally runs, not how strong any given day is.
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.
April 1 to May 31
“Rocky Mountain juniper pollinates April to May, juniper "berries" mature October to December of the second year following pollination.”
Utah State University Extension (Range Plants of Utah)
USU gives months for Rocky Mountain juniper; Utah juniper (J. osteosperma), which covers nearly one fifth of the state, is not month-dated on the companion USU page, and lower-elevation juniper can shed pollen earlier in spring.
April 15 to July 31
“As the year progresses, grasses will emerge and their pollen will cause symptoms through most of the summer - typically April to July.”
University of Colorado Anschutz Medical Campus
Regional source: Mountain West academic medical campus in Colorado stating U.S.-general timing, applied to Utah with a mid-April start for the high-elevation climate. University of Utah Health pages that state Utah months directly block automated access and could not be quoted.
August 1 to October 8 ❄ end derived from median first frost
“Flowers August to September and reproduces from seed.”
Utah State University Extension (Range Plants of Utah) · end date computed by us from NOAA 1991 to 2020 frost normals, not published by the source
Sourced flowering window is August to September; cold fall weather ends the season, so the end is computed from first frost. Sagebrush stands in for ragweed as the dominant fall aeroallergen in the Great Basin.
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.
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.
This page derives the end date from that rule: Utah's median first fall frost is October 8 (NOAA 1991 to 2020 normals, the same number our first frost pages publish), and that is the derived end date on the ragweed bar above. It is a median: about half of years frost earlier, half later, and EPA's indicator work shows fall frosts arriving later than they used to across the northern states, which is exactly why ragweed seasons have been getting longer.
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 Utah’s tree pollen season is ahead of or behind schedule this year.
The live grid currently holds the finished spring of 2026, shown as history. Tree windows above are not shifted by it; readings for the coming spring start filling in from late January.
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.
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.
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.
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.
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: “Artemisia tridentata (common sagebrush)” by James St. John, CC BY 2.0