Pollen grains are tiny particles that flowering plants produce by the millions. The grains contain genetic material necessary for the fertilization and survival of plant species. On its own, pollen is a relatively harmless substance. However, when it's inhaled or reaches the eyes of many humans, a reaction is triggered - the sneezing and watery eyes begin.
There are two main types of pollen. Each corresponds to the plant's method of pollination.
Wind-borne pollinating plants produce pollen that is light and practically invisible. Easily inhaled, this is the type that causes the allergic reactions. Although "wind-borne" and often carried very far away, most of it stays close to the source. Wind-borne pollen can collect on anything and it sometimes gives other plants a bad rap.
Most ornamental shrubs, annuals and perennials are safe. Oddly enough, the clouds and layers of pollen we see from pine trees is usually not allergy-provoking. Fruit trees are pollinated by insects and are also safe. Plants with strong fragrances can also prompt allergic reactions that are not necessarily related to pollen.
Insect-pollinated plants produce grains that are larger, heavier and sticky. These types in general are not irritants. Carried by insects and animals from plant to plant, these pollens are readily visible.
Pollen of both types range in size and protein makeup; therefore they also range in levels of allergic aggravation.
Tree pollen is number one on the list. The major suppliers of wind-borne pollens are oak, birch, most maples, ash and alder. Lesser tree allergen contributors include acacia, hickory, mesquite and sycamore. These trees bloom before they produce leaves — one of the keys to wind-borne pollen. The season begins in late winter and carries over into spring.
Weed and grass pollens are next. The most notorious pollen-producing weeds are from the ragweed family. Chrysanthemums, daisies and marigolds are members of this group. Most common turfgrasses do not produce pollen and will not if kept mowed at their proper height. Late spring into summer and fall are the season for these plants.