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Hartford, Connecticut sits in the Connecticut River Valley, where a humid continental climate, mixed hardwood forests, and ample rainfall create a long and intense allergy season spanning roughly March through October.
Tree pollen kicks things off in early spring, with oak, birch, maple, ash, hickory, and Eastern red cedar driving symptoms from late March through May; oak and birch typically produce the most severe peaks in April.
As tree pollen wanes, grass pollen takes over from mid-May through July, dominated by timothy, Kentucky bluegrass, orchard grass, and rye, with counts often highest in June.
Late summer and fall bring weed pollen, led by common and giant ragweed beginning in mid-August and persisting until the first hard frost in October; pigweed, lamb's quarters, and plantain add to the load.
Transitional periods—late May (trees and grasses) and late August (grasses and ragweed)—can amplify symptoms as allergens overlap.
Beyond pollen, the region's humidity fuels outdoor mold spores, especially from decaying leaves in fall, while indoor dust mites thrive in sealed winter homes. Urban traffic corridors along I-84 and I-91 can worsen reactions through particulate pollution.
Overall, Hartford's profile is defined by a prolonged, multi-phase season with significant tree and ragweed burdens intensified by valley humidity.