The purpose of this publication is twofold. It will first explore general information on plants and their allergenic properties, and second, it will be a quick ready-reference to allergenic plants that could create a problem for you. Many people still believe that allergies are all in someone’s mind. However, many are found in our own backyards. It is important to remember that pollens cause not all allergies. Dust, molds, mildews, and animals cause many.
There are many misconceptions in the Southern Nevada area about which plants do and do not contribute to allergy problems. One must first understand allergies and how people are affected. Determining what causes an allergy may be difficult for most people, as the reactions may take some time to surface. Most people have immediate reactions that show within thirty minutes. Others can have delayed reactions, taking many hours for symptoms to appear. Some allergenic reactions to newly introduced plants may take years before showing up.
Such was the case during World War II when US farmers began growing caster beans for the war effort. It was only after a few years that the real impact of the pollen from these large plantings of caster beans began to affect the people around the areas where they were growing. It has been known for years that olives and fruitless mulberries cause allergy problems in southern Nevada. Both of these trees grow well in the southern Nevada climate and soils. However, much of the population suffers from the allergens they produce. Part of the problem is that these trees have been overplanted, much like the WWII plantings of castor beans, without taking care to select those that would have less pollen. Now they have been banned or highly discouraged in many communities.
Recently there has been an effort to find and use a pollen-free olive (Swan) but no known effort to find low-pollen producing fruitless mulberries. Male trees are often planted because people think they will require less care, as they do not produce messy fruit to clean up like the female trees. But the pollen they produce can be more of a problem for allergy sufferers. Some references suggest that trees and shrubs, such as ash, poplar, and willow, should not be planted because of the pollen the male trees produce. They overlook the fact that the female tree of the species would be just fine. With few or no males planted in the area, the fruit product is reduced or eliminated.
Part of the problem is that we keep searching and selecting what we think will be a maintenance free tree or shrub. By doing so, we often cause more problems. A dioecious tree or shrub is one that has male or female flowers on separate plants. Because the female and male flowers are found on separate trees, the males produce flowers with large quantities of pollen to insure pollination of the female plants. This factor makes our maintenance-free plants now an allergenic problem. Add this to all the other air pollution problems, and the combination becomes a serious problem in urban areas. Without good horticultural planning, city and state parks and developers can create problems that result in the suffering of many people.
The answer is not banning plants, but understanding how and why plants cause these problems, from a sound environmental horticultural perspective.
Allergy sufferers should not have to live in sterile landscapes with few if any plants. Landscapes can and should be beneficial to the total environment. When buying plants one should always buy by scientific name and check a good reference book. Sir Francis Bacon said that “Gardening is the purest of human pleasures" and so it should be, but will not be as long as one cannot go outside because of allergies.
Allergies will continue to be a problem as more of the population ages past 50. Those without allergies now will begin to develop them. This problem will continue to escalate as the population continues to age and people continue to be exposed to chemical pesticides, diesel fumes, and waste gases. Even the rubber particles that wear off auto tires contribute to the problem. It is interesting that these rubber particles can cause allergic reactions to the pollen of plants that are related to the true rubber tree in the landscape. There also seems to be a correlation between many of the desert legumes that are planted because they make their own nitrogen. They can also contribute to allergies with peanuts. To much of anything may cause problems.
Avoidance is the key to allergy relief. There still are those who say there is little we can do to change this problem, as most air-born pollen is from weeds that come in from undeveloped areas. It may seem unlikely that reducing the number of allergenic plants in a single yard would make a difference. However, a survey in San Luis Obispo, California, (by Thomas Leo Ogren) showed that the expected weeds that are blamed for allergies such as ragweed were not to be found. The allergy problems were from common landscape plants. This is true of Southern Nevada. It was found that a male pepper tree (Shinus mollie) in a yard exposed the homeowner to ten times the pollen than one in the neighbor's yard. Eliminating allergenic plants close to homes can reduce symptoms. What you plant does make a difference. Just as a new urban forest begins with a few trees planted in one yard, so does an allergenic free environment begin in one yard, and spread to an allergenic free city.
For more in-depth information, check your local library or bookstore for “Allergy-Free Gardening,” by Thomas Leo Ogren, or the internet “Allergenic Plants in landscapes.”
The following list should help in achieving an allergy-free yard. As most pollens travel only short distances just landscaping your yard with low allergen plants will help. All species of grass that produce male flowers can be allergenic, but some like Bermuda are more prone to causing allergies.
For a complete list of "low, medium and high allergenic plants" use the link below to download the PDF version of this factsheet.
Master Gardeners of Nevada
Program trains local gardeners to provide research-based horticulture information to Nevadans
Master Gardeners of Washoe County
Master Gardeners provide free, research-based horticulture information to Nevadans.
Integrated Pest Management
Integrated Pest Management program is a long-term management strategy that uses a combination of tactics to reduce pests to tolerable levels with potentially lower costs for the pest manager and minimal effect on the environment.
Robinson, M. L., 2000, Allergenic Plants in Southern Nevada (Landscaping for an allergy free yard), Extension, University of Nevada, Reno SP-00-28
An EEO/AA Institution. Copyright ©
2023, University of Nevada Cooperative Extension.
A partnership of Nevada counties; University of Nevada, Reno; and the U.S. Department of Agriculture