The pollen count in Las Vegas peaks in March–October, though allergy sufferers can experience symptoms from as early as late winter. Despite low humidity, the Southwest sees heavy pollen from mulberry, olive, and native desert plants.
The primary driver is Mulberry — mulberry trees are prolific pollinators and a major trigger of allergies in warm, dry climates. On warm, dry, and windy days the pollen count in Las Vegas 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.