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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - January 31, 2012

From: Austin, TX
Region: Southwest
Topic: Pollinators, Compost and Mulch, Problem Plants, Groundcovers, Grasses or Grass-like, Shrubs, Trees, Wildflowers
Title: Reducing Allergens in Yards and Gardens
Answered by: Janice Kvale

QUESTION:

What are some allergen-free native plants to Central Texas that thrive in the soil and can survive in the weather?

ANSWER:

This is a great question and you are not alone. One of every six Americans reacts to environmental allergens so it is an important topic. Unless one lives in the Arctic or Antarctic, there are plant allergens everywhere.

You don't indicate the kind of plants you have in mind (grasses, flowers, ground covers, trees), so I will list a few low allergen plants and give you references for more information. Also, you didn’t ask, but there are other actions a gardener can take to keep allergies at bay and I am including that information also.

You may not be surprised to learn that sex causes some of the problems. Pollens are produced only by male members of various species. There may be a preference for male specimens among landscapers and nurseries because home owners do not want the "mess" that female plants make with their fruits and seeds. Nervertheless, planting female trees reduces wind-blown pollen and traps much of the pollen that blows in from everyone else's trees and grasses.  Malpighia glabra (Acerola), Cornus florida (Flowering dogwood), and Magnolia virginiana (Sweetbay) are relatively low allergen trees. The ornamental shrubs that may be purchased as female specimens include Ilex vomitoria (Yaupon) and Ilex opaca (American holly). The female version of  Acer rubrum (Red maple) is a low pollinator. Note that the difference between a tree and a shrub is often whether it is pruned or allowed to grow. 

The good news is that plants with colorful, showy flowers are pollinated by insects and birds rather than by pollen blowing in the wind. The pollen that you see on some of these flowers is too heavy to blow around and not likely the pollen that is causing problems. Among the plethora of options consider Callirhoe involucrata (Winecup) and Penstemon cobaea (Wild foxglove) for starters. However, avoid those with strong aromas since some persons react allergically to scents.

There are so many beautiful native plants that are pollinated by bees, birds, butterflies, and moths that you may want to do your own search on our website. To explore plants, go to http://www.wildflower.org/plants/and click on Native Plant Database. Then select location (your state), habit (herb, shrub, tree, etc.), and duration (perennial). Check the requirements of your site: light requirement (sun, part shade, shade) and soil moisture (dry, moist, wet) and see what comes up. The plants I have listed are found in Texas; readers living elsewhere may use this method to find plants for any other North American location.

Keep any lawn areas mowed to prevent the grasses from seeding. You may not want ornamental grasses in your yard unless you can locate a supplier who carries female grasses. Ground covers may be preferable to grasses. Consider Phlox pilosa (Downy phlox) or Dichondra argentea (Silver ponyfoot). Likewise keep hedges trimmed as they can trap pollens blowing in from elsewhere.

Molds are high on the list of allergens. Molds occur in compost and mulches, such as cocoa hulls and bark mulches.

Time of day makes a difference. Peak pollen production is most active from 3 A.M. to 8 A.M. and later between 5 and 9 P.M. Weather can influence the presence of pollens. A long, gentle rain may wash away pollens. Worse are hot, dry, windy days. High humidity reduces pollen production; high temperatures increases it. This is especially true of grass pollens. That said, working outside during lowest pollen production means you balance the time of day with the weather. If you cannot avoid exposure to pollens, limit it by covering your exposed skin and hair and showering when you are done with yard work. Consider using a mask when working on windy days or mowing lawn.

The topic of plants and allergies has been addressed briefly for a few other questioners of Mr. Smarty Plants and you may with to check those also at http://www.wildflower.org/expert/search.php?start=0&keyword=allergies&pagecount=10. The following sites have basic information on allergy-free gardening: http://pss.uvm.edu/ppp/pubs/oh71allergies.htm; http://forums.gardenweb.com/forums/load/neweng/msg0812171413316.html.

Finally, a textbook reference available at  http://www.allergyfree-gardening.com/home.html or through your public library is Allergy-free gardening: the revolutionary guide to healthy landscaping by Thomas Leo Ogren. Ogren has developed a 1-10 scale for many plant species depending on their pollen production and contribution to allergic response in humans and pets. Lower numbers are less allergenic. All of the plants I have mentioned are ranked between 1 and 5 on Ogren's scale. His website also has much good information.

Here's hoping your future garden does not leave you sneezing or worse!

 

From the Image Gallery


Barbados cherry
Malpighia glabra

Flowering dogwood
Cornus florida

Sweetbay
Magnolia virginiana

Yaupon
Ilex vomitoria

American holly
Ilex opaca

Red maple
Acer rubrum

Winecup
Callirhoe involucrata

Prairie penstemon
Penstemon cobaea

Downy phlox
Phlox pilosa

Silver ponyfoot
Dichondra argentea

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