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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog
Silver maple flowers in the spring.

Allergenic Plants


If you are an allergy sufferer, spring often brings sniffling, sneezing, and watery eyes. One culprit is pollen from flowers of trees, shrubs, grasses, and weeds. Though most of these bloom for just a short period each year, something is almost always blooming. In early spring, the trees and shrubs are blooming. In summer the main pollen source is from flowering grasses. In late summer and fall, weedy plants from roadsides are the problem.

Pollen is an important part of plant reproduction and must be moved around from flower to flower. We all know that showy flowers attract insects such as bees, which help pollinate the flowers. Not all plants use insects to spread their pollen. Most plants that cause allergies use wind to spread their pollen. Therefore, these plants typically have abundant pollen and not very noticeable flowers.

Fortunately, not all pollen causes allergies. Ample research has been done in this area to determine which plants are the culprits. Allergenic trees are usually a problem from March through May and include the following (in flowering order): Maple, Willow, Poplar, Elm, Birch, Mulberry, Ash, Hickory, Oak, and Walnut.

Grasses are more powerful allergens than trees and bloom from May through summer. A few allergenic grasses include orchardgrass, bluegrass, timothy, johnsongrass, bermudagrass, and redtop.

Late summer and fall allergenic plants include many weeds such as ragweed, pigweed, lambsquarters, and wormwood. Common and giant ragweeds are serious hazards to hayfever sufferers. Both types of ragweed are included on the Illinois noxious weed list for municipalities. It is illegal to allow ragweed to grow on ground you own or work on within any municipality in Illinois.

The best way for you to manage these pollen producers in the landscape is through proper identification. You need to be able to recognize and identify plants that produce irritating pollen. Admittedly, you cannot completely eliminate allergies no matter what you do since air-borne pollen travels great distances; but you can improve the immediate area where you live.

Existing tree pollen is hard to manage, but if you are an allergy sufferer choose non-allergenic trees when planting your next tree. Since the greatest allergy offenders are grasses and weeds, try to keep them from blooming through mowing and weed management programs. For some dioecious plants, you can plant the female instead of the male plants, since the males produce pollen (but remember that female plants produce all those seeds).

Pollen (and mold) counts are routinely provided through the nightly news or on the Internet. Each provides counts for our area and includes the source of allergens. Counts are usually ranked from low (one) to high (ten) and indicate to allergy sufferers who are allergic to these pollens or mold, the potential for symptoms of hay fever or asthma.



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