The pollen count in Los Angeles peaks in February–May, though allergy sufferers can experience symptoms from as early as late winter. California's Mediterranean climate produces a long pollen season from February through June.
The primary driver is Olive — olive pollen is highly allergenic and growing in concern as olive trees spread across the Southwest. On warm, dry, and windy days the pollen count in Los Angeles can spike dramatically, while rain temporarily brings it down.
Tree pollen starts in late winter and runs through spring. Grass pollen peaks during spring. Weed pollen is less of a concern in the west region.