Allergenic plants
allergenic plant
February 11, 2013
  • /ACES
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URBANA -- If you are an allergy sufferer, spring often brings sniffling, sneezing, and watery eyes, said a University of Illinois Extension horticulture educator.

“One culprit is pollen from flowers of trees, shrubs, grasses, and weeds,” explained Rhonda Ferree. “Though most of these bloom for just a short period, something is almost always blooming. In early spring, it’s the trees and shrubs. In summer the main pollen source is 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. Showy flowers attract insects such as bees, which help pollinate the flowers, but not all plants use insects. 

“Most plants that cause allergies use wind to spread their pollen,” she said. “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 orchard grass, bluegrass, timothy, Johnson grass, Bermuda grass, and redtop. 

“Late-summer and fall allergenic plants include many weeds such as ragweed, pigweed, lambs quarters, and wormwood,” Ferree explained. “Common and giant ragweeds are serious hazards to hay fever 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 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,” she said. “Admittedly, you cannot completely eliminate allergies no matter what you do because airborne 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. The greatest allergy offenders are grasses and weeds, so 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, because it’s the males that 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 the local area and lists the allergen sources. Counts are usually ranked from low (1) to high (10) and indicate to allergy sufferers the potential for symptoms of hay fever or asthma.