|Generally, the pollen season can be subdivided into three distinct seasons, each of which can affect different people. Early spring is when trees pollinate. Grasses pollinate during the summer, and weeds pollinate late summer into the fall. In Colorado, trees generally begin pollinating in February and continue through June. Grass pollen season runs from early May through August, and weed pollen is in the air in August and September.
Pollen counts can vary widely from day to day depending on weather conditions. Generally, pollen levels increase on warm, sunny days. Windy days also commonly have higher pollen levels. Rain washes pollen out of the air, reducing pollen counts. Cool, damp weather also tends to keep pollen levels low. Yearlong allergens include our pets, indoor and outdoor molds.