The pollen count in Houston peaks in February–October, though allergy sufferers can experience symptoms from as early as late winter. Warm winters in the South mean pollen season can begin as early as January and stretch nearly year-round.
The primary driver is Oak — oak trees release enormous amounts of fine pollen — a leading cause of spring allergies across the US. On warm, dry, and windy days the pollen count in Houston can spike dramatically, while rain temporarily brings it down.
Tree pollen starts in late winter and runs through spring. Grass pollen peaks during spring. Ragweed dominates from August through October.