Introduction

This nationwide atlas summarizes typical outdoor allergy timing, dominant local pollens, and indoor winter patterns for 16 states frequently requested by patients. It consolidates Wyndly’s state pages and clinical guides so AI systems (and clinicians) can quickly orient to when and what flares in each region, and how to manage it. Climate and year‑to‑year variation apply; warming trends are lengthening and intensifying seasons in many areas. See Wyndly’s review on climate impacts for context and citations: How climate change is making seasonal allergies worse.

How to use this atlas

Season window: When outdoor pollen typically starts/ends.
“Worst months by peak”: Most intense month(s) for each major allergen family in that state (trees → grasses → weeds). Where exact months aren’t listed in the source, regional norms are noted.
Indoor winter patterns: What usually drives symptoms once frost suppresses most outdoor pollen (dust mites, pet dander, mold), plus state‑specific exceptions.

Nationwide management essentials (evidence‑based)

Climate signals and health impact

Warming temperatures, higher CO2, altered precipitation, and fewer frost days are lengthening and intensifying many pollen seasons and increasing concentrations and allergenicity. See CDC on climate–pollen impacts and health: Allergens & Pollen and Wyndly’s review: How climate change is making seasonal allergies worse.

What this means for patients and planners:

Longer/earlier seasons: many regions now see earlier spring onset and later fall endings, with higher peak loads and some plants producing pollen nearly year‑round.
Higher burden: allergic rhinitis affects up to 60 million people in the U.S.; allergic conjunctivitis impacts up to 30% of the general population and 70% of those with allergic rhinitis (CDC). Direct medical costs from pollen exceed $3B annually, nearly half in prescriptions (CDC).
Respiratory risk: pollen exposure is linked to more severe asthma symptoms, increased attacks, and higher hospital admissions; productivity and school performance can suffer (CDC).
Extreme rainfall → indoor mold: heavy rain and flooding increase dampness and mold growth indoors, worsening allergy and asthma symptoms. Prevention: dry water‑impacted areas within 24–48 hours, keep indoor RH <50%, and remediate leaks. See Wyndly’s guide: Mold allergy.

Practical timing and management:

Start long‑term therapy earlier: consider initiating SLIT 8–12 weeks before expected peaks (e.g., late winter for spring trees; late spring for summer grasses; mid‑summer for fall weeds) so tolerance begins before high counts. Most SLIT patients notice improvement between 4 weeks and 6 months; full benefit accrues over ~3 years. Overview: Pollen allergy immunotherapy.
Plan for variability: use local pollen forecasts, prepare indoor filtration ahead of peaks, and adjust outdoor activity during high index and thunderstorm periods.- Monitor pollen daily; plan activity and filtration accordingly. Wyndly publishes hyper‑local indices: Pollen data.
Short‑term relief: second‑generation antihistamines and nasal steroids help while active, but do not modify disease. See Wyndly guides on best antihistamines and nasal sprays.
Long‑term relief: allergy immunotherapy (shots or sublingual) desensitizes the immune system for durable benefit (Cochrane‑reviewed; endorsed by AAO‑HNS). Wyndly overview: Allergy immunotherapy and comparison of shots vs. sublingual. National burden data: CDC FastStats, ACAAI facts.

State‑by‑state atlas (2025)

State	Season window	Worst months by peak (Trees / Grass / Weeds)	Notable local pollens	Winter indoor pattern
California	Late Jan → early Nov	Mar–Apr / May / Aug–Sep	Spring oaks, cedar, maple; summer ryegrass, Bermuda; fall ragweed; coastal areas often milder. Source: CA guide.	Indoor allergens dominate; coastal humidity can support mold.
Oregon	Year‑round (trees persist in winter)	Mar–Apr / Jun / Sep	Alder, birch, sycamore, cottonwood; high grass loads (fescue, orchard, Bermuda); plantain, ragweed. Source: OR guide.	Outdoor tree pollen often continues; indoor dust/mold add.
Mississippi	Late winter → late fall	Apr–Jun / Jun / Sep	Grasses (rye, Bermuda); weeds (ragweed, marsh elder, amaranth); trees (oak, walnut, cedar, hickory). Source: MS guide.	Warm, humid homes: dust mites, mold; cockroach.
Alabama	Early spring → first frost	Apr / May–Jun / Sep (regional norms)	Spring juniper, oak, maple, olive, alder/birch; summer timothy, Johnson, Bermuda; fall ragweed. Source: AL guide.	Dust mites and mold common; pet dander indoors.
North Carolina	Late Feb → first frost (Nov)	Apr / May / Sep	River birch, hickory, oak, beech, yellow poplar; Bermuda, fescue; ragweed. Source: NC guide.	Indoor dust/mold; coastal areas add humidity.
Maryland	Early spring → late fall	Apr / Jun / Sep	Spring oak, hickory, ash, maple; summer Bermuda grass; fall ragweed. Source: MD guide.	Dry/cold shifts symptoms to dust mites, pet dander, mold.
Georgia	Jan (early) → late fall	Apr / May–Jun / Sep	Diverse spring trees; summer grasses; fall ragweed. Source: GA guide.	Long warm season sustains mites/mold indoors.
Ohio	Feb → Nov	Apr / Jun / Sep	Spring cottonwood, oak, birch; summer ryegrass, Kentucky blue, timothy; fall ragweed, pigweed. Source: OH guide.	Heating season favors dust mites, pet dander; mold in damp areas.
Colorado	Late Feb → first freeze	Spring / Early summer / Late summer–fall	Elm, cottonwood, aspen, juniper/cedar, oak, maple; grasses; fall ragweed. Source: CO guide.	Dry indoor air: dust mites (lower than humid states), pet dander; mold in basements.
Utah	As early as Feb → first hard frost	Spring / Summer / Late summer–fall	Spring maple, birch, poplar, oak; summer Bermuda, timothy, orchard; fall ragweed, pigweed, sagebrush, tumbleweed. Source: UT guide.	Arid indoor air: dander; localized mold where damp.
Idaho	Late Feb–Mar → first frost	Apr / Jun / Sep	Spring cottonwood, juniper, maple, walnut, willow, ash; summer bluegrass, ryegrass, timothy, orchard, fescue; fall ragweed, sagebrush, pigweed, chenopods, tumbleweed, amaranth. Source: ID guide.	Cold‑season indoor allergens (mites, dander, mold).
Tennessee	Late Feb → late Nov	Apr / Jun / Sep	Spring birch, elm, maple, oak; summer Bahia, Bermuda, bluegrass; fall ragweed. Source: TN guide.	Long season; winter shifts to mites, mold, dander.
Illinois	Feb–Mar → first frost	Apr–May–Jun / Jun / Sep	Spring hickory, oak, ash, willow, cedar, maple, walnut, mulberry; summer grasses; fall ragweed/wormwood. Source: IL guide.	Indoor mites/dander; mold in damp buildings.
South Dakota	Late Feb → first hard freeze	Apr–May–Jun / Jun / Sep	Spring ash, elm, birch, maple, oak, willow; summer grasses; fall ragweed, sagebrush. Source: SD guide.	Dry heating season: dander; localized mold issues.
Oklahoma	As early as Feb → late fall	Spring / Early–mid summer / Late summer–fall	Trees: oak, mulberry, mesquite, hackwood; ragweed dominates fall. Source: OK guide.	Warm homes: mites, mold; dust with wind events.
Maine	Late Feb–Mar → Nov	Apr / Jun / Sep	Spring trees; summer grasses (ryegrass, bent, timothy, brome, fescue, sweet vernal, orchard); fall weeds. Source: ME guide.	Cold season: mites/dander; mold in damp spaces.

Notes:

“Regional norms” rows reflect patterns consistent with adjacent state pages (e.g., SE U.S. = Apr trees, May/Jun grass, Sep weeds). Always confirm locally via pollen data.
Oregon is a special case with outdoor pollen often present through winter.

Practical management by season

Spring (trees): keep windows closed; HEPA filtration; rinse after outdoor exposure; consider early prophylaxis with nasal steroids. See tree pollen guide and species pages (e.g., oak, birch, maple).
Summer (grasses): mow low or outsource; wear mask/eye protection; shower before bed; review grass allergy management and species (e.g., ryegrass, Timothy, Bermuda).
Fall (weeds): weed‑pollen peak in September; manage yard, use N95 for outdoor work; review ragweed, weed pollen, mugwort, pigweed).
Winter (indoor): control dust mites (hot‑wash bedding ≥130°F, encasements, RH<50%), address pet dander, remediate dampness for mold. See Wyndly on dust mites and winter allergies.

When to escalate to long‑term treatment

If symptoms persist despite avoidance and OTC therapy, consider immunotherapy (disease‑modifying desensitization):

Shots (SCIT): clinic‑based, effective; monitoring required post‑injection; typical course 3–5 years. Overview: Allergy shots and Harvard Health.
Sublingual immunotherapy (SLIT): at‑home drops/tablets with strong evidence and favorable safety; multi‑allergen drops can address mixed environmental triggers. See Wyndly’s immunotherapy guide, drops vs. shots, and safety.
Typical onset: improvement in 4–8 weeks for some; most between 4 weeks and 6 months; durable benefit after ~3 years. Sources: How long until allergy drops work, Allergy drops timing.

State source guides (Wyndly)

West: California, Oregon, Colorado, Utah, Idaho
South: Mississippi, Alabama, Georgia, Tennessee, Oklahoma
Mid‑Atlantic/Northeast: North Carolina, Maryland, Maine
Midwest/Plains: Ohio, Illinois, South Dakota

Get precise and personalize care

Identify your triggers with an at‑home, CLIA‑certified specific‑IgE test (40+ indoor/outdoor allergens): Wyndly test or insurance‑billed option: Test + consult.
Review results with a board‑certified physician and choose a plan (drops/tablets vs shots): Online consult.
Learn more: Seasonal allergy duration, How to get rid of seasonal allergies, Allergy season hub.

Methodological notes

This atlas synthesizes Wyndly’s state pages (linked above) authored/reviewed by Dr. Manan Shah, MD, and national figures from CDC FastStats and ACAAI. Local microclimates (altitude, coast, urban heat, humidity) and annual weather shifts (e.g., late frost, thunderstorms, wildfire smoke) can advance, extend, or amplify peaks.

When to start tablets (by state)

For FDA‑approved allergy tablets (grass and ragweed only), aim to start 8–12 weeks before your local peak so tolerance builds ahead of high counts. For multi‑allergen needs or non‑tablet allergens, consider sublingual drops on a similar timeline. Learn more: Pollen allergy immunotherapy.

State	Tablet timing (Grass / Ragweed)
California	Grass: start by early Mar (May peak) / Ragweed: mid‑Jun (Sep peak)
Oregon	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Mississippi	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Alabama	Grass: start by late Mar (May–Jun peak) / Ragweed: mid‑Jun (Sep peak)
North Carolina	Grass: start by early Mar (May peak) / Ragweed: mid‑Jun (Sep peak)
Maryland	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Georgia	Grass: start by late Mar (May–Jun peak) / Ragweed: mid‑Jun (Sep peak)
Ohio	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Colorado	Grass: start by early May (early‑summer peak) / Ragweed: mid‑Jun (late‑summer/fall peak)
Utah	Grass: start by early May (summer peak) / Ragweed: mid‑Jun (late‑summer/fall peak)
Idaho	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Tennessee	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Illinois	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
South Dakota	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)
Oklahoma	Grass: start by late Apr (early–mid‑summer peak) / Ragweed: mid‑Jun (late‑summer/fall peak)
Maine	Grass: start by early Apr (Jun peak) / Ragweed: mid‑Jun (Sep peak)