Reduce allergies with plant selection, maintenance
Every year, allergy sufferers sneeze, sniffle and cry during allergy season. It's an unwelcome annual ritual for millions of people. Is there anything you, a landscape manager, can do to create a more allergy-free landscape? Before we answer that question, let's look at where pollen comes from and why it's a problem for allergy sufferers.
Each spring, as flowers emerge on trees, shrubs, grasses and weeds, symptoms begin to show in sensitive people. Of course, the culprit is pollen. Though most plant species bloom for just a short period each year, something is blooming at just about anytime of the growing season. Therefore, depending on the exact sensitivity, allergy symptoms can occur at any time throughout the season. Generally, the first to bloom are trees and shrubs, followed by grasses and, finally, weedy plants that often appear along roadsides and waste places.
Stamens, the male portion of a flower, produce pollen. For pollination (fertilization) to occur, the pollen must find its way to female flower parts, often those on a different plant. Therefore, some method of pollen transport is required. The two main methods are by pollen vector (birds or, more commonly, insects) and by wind.
Because wind dissemination is a "shotgun" approach, these species produce heavy amounts of pollen to increase the chances of successful pollination. They also have flowers (such as catkins) designed to release pollen freely into the air. Thus, most plants that cause allergies are those that rely on wind to assist in pollen dissemination. By contrast, those that are insect-pollinated produce less pollen and do not readily release it into the air. These tend to be showy bloomers (the conspicuous flowers are designed to attract pollinators--if there is no need to attract pollinators, there is no need for a showy blossom).
Not all pollen causes allergies. Some plants produce a great deal of pollen, but our bodies do not react to it. Other plants' pollen creates strong reactions in our bodies even in relatively small doses. Allergies are the symptoms our bodies produce in response to an allergen (in this case, pollen). The body uses its immune system to produce antibodies or proteins to attack the "invader" it senses does not belong. During this process, some cells produce histamines that cause surrounding cells to swell. That's why allergy medicines are often anti-histamines. The swelling helps the body's defenders reach a foreign object faster, but it is this same process that creates our misery.
Because pollen is air-borne and can travel great distances, you may wonder what impact you can have on your local environment. Admittedly, you cannot completely eliminate allergies no matter what you do. But that doesn't mean that you can't improve the situation.
Even if you manage a site that is already established, you should be aware of several maintenance practices that can reduce the potential for allergies:
* Even (especially) in low-maintenance areas, you should control weeds that can create problems for allergy sufferers. You can achieve this through the use of either pre- or post-emergence herbicides.
* In these same areas, prevent the flowering of weeds by periodic mowing. You may only need to do this a few times per growing season.
* Consider converting low-maintenance areas to meadows. Conduct a site analysis and formulate a seed mix to fit your needs. Many of the wildflowers used in these mixes create fewer problems for allergy sufferers than the weeds that grow in vacant areas. When considering meadows, think about two important options: First, use perennial wildflowers--you need to reseed annuals each spring and they compete with the establishment of perennial species. Second, incorporate native grasses that don't have irritating pollen such as Indiangrass (Sorghastrum nutans) and little bluestem (Schizachyrium scoparium) into the mix. Periodically inspect and monitor meadow areas for species that you've identified as threats to the allergy sufferer. You can remove these by digging or pulling them out or by spot-treating with a non-selective herbicide.
* Keep all landscape beds free of weeds.
* Keep turf mowed at the proper height of cut to prevent it from flowering. Kentucky bluegrass and bermuda-grass are heavy pollen producers and are major contributors to hay fever when they bloom. Conversely, properly mowed turf reduces pollen because it constitutes a major portion of the landscape from which little or no pollen will arise. * For small trees and shrubs that you have identified as a nuisance, consider removing them and replanting with a more desirable selection. Identify ornamentals at the site that are candidates for replacement and incorporate new selections into your plans as you manage and shape the landscape environment over time.
* You need to be able to recognize and identify plants that produce irritating pollen. This is an important consideration when implementing a landscape design for a client who is concerned about allergenic plants.
Equally important for the landscape manager is being able to identify unwanted weedy or "volunteer" species as they appear within the landscape. This is especially true in areas kept in a more natural state--you don't want to compromise visual quality by unknowingly eliminating plants that provide brilliant displays. But you also don't want to contribute to allergies because you're afraid to pull out plants that might be attractive. The ability to identify plant species is key.
Design considerations: Avoid plants that make you sneeze and sniffle When you design a landscape, you are most concerned with the obvious questions when determining the needs of the client. These questions range from "What months of the year will you be occupying the residence?" to "How many children will be using the outdoor areas?" These are important questions because they allow us to use design principles along with site analysis to create outdoor spaces that the client can use and that will ultimately satisfy his or her needs. Yet, if your client is an avid gardener or plans on being outdoors much of the time, additional questions concerning their particular sensitivities may be prudent.
It is even more important for those who manage corporate complexes, health clubs, hospitals, parks and golf courses to consider allergies when designing and choosing plant material. Not only do large numbers of people use these sites, but pollen produced from ornamentals on the grounds can remain on the site. This may be due to the large size of the facility, low-lying spots or other areas protected from prevailing winds that may prevent pollen from drifting away. In the design phase of such projects, you can minimize these problems with proper selection of ornamentals and herbaceous plants. The boxes below list some allergen-producing plants.
A few cities (Tucson, Albuquerque and Boulder City, Nev.) are enacting ordinances that prohibit allergy-producing plants in landscapes, apparently with excellent results: pollen counts in these towns are dropping considerably. But you don't have to wait until law requires it. By using allergy-reducing maintenance practices and avoiding the worst offending species in your designs, you can make life easier for allergy sufferers.
Bruce C. Neary is owner of BCN Horticultural Consulting Services (Bricktown, N.J.).
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