Pollen Count in Pasadena, CA

Pasadena's location in the San Gabriel Valley, with its mild Mediterranean climate, warm dry summers, and proximity to foothill chaparral, creates a long and active allergy season that often stretches nearly year-round.

Tree pollen is the earliest major trigger, typically ramping up from February through May, with oak, sycamore, mulberry, olive, ash, and the ubiquitous non-native Italian cypress producing heavy loads—olive and mulberry are particularly potent, though city ordinances have limited new plantings.

As trees taper off, grass pollen takes over from late April into July, driven largely by Bermuda grass, ryegrass, and fescue common in Southern California lawns and parks; Bermuda can continue releasing pollen well into early fall.

Weed season follows from late summer through November, dominated by ragweed, sagebrush, pigweed, Russian thistle (tumbleweed), and lamb's quarters blown in from surrounding open spaces and foothills.

Overlap between late-season grasses and early fall weeds frequently intensifies symptoms in August and September.

Beyond pollen, Pasadena residents contend with year-round dust, outdoor mold spores that spike after rain, wildfire smoke, and persistent ozone and particulate pollution trapped against the San Gabriel Mountains.

Overall, Pasadena's allergy profile is defined by prolonged exposure, diverse plant sources, and compounding air-quality stressors.