What Is the Pollen Count?


A sure sign of spring (or summer or fall) in many regions of the United States is news media reports of pollen counts. These counts are of interest to some 35 million Americans who get hay fever because they are allergic to pollen.

The pollen count tells us how many grains of plant pollen were in a certain amount of air often one cubic meter during a set period of time, usually 24 hours. Pollen is a very fine powder released by trees, weeds and grasses. It is carried to another plant of the same kind, to pollinate the indication of new seeds. This is called pollination.

Bees and other insects carry the pollen of some plants from plant to plant. These plants usually have brightly colored flowers and sweet scents to attract insects. They seldom cause allergic reactions. Other plants rely on the wind to carry pollen from plant to plant. These plants have small, drab flowers and little scent. These are the plants that cause most allergic reactions, or hay fever.

When circumstances are right, a plant starts to pollinate. Weather affects how much pollen is carried in the air each year, but it has less effect on when pollination occurs. As a rule, weeds pollinate in late summer and fall. The weed that causes 75 percent of all hay fever is ragweed, which has numerous species. One ragweed plant is estimated to produce up to 1 billion pollen grains. Other weeds that cause hypersensitive reactions are cocklebur, lamb's quarters, plantain, pigweed, tumbleweed or Russian thistle and sagebrush.