The Allergy-Fighting Garden

Early in his book, Thomas Leo Ogren points out that allergies in the United States have greatly increased over the last sixty years and are increasing at a rate of 2 to 3 percent each year. Less than 5 percent of the U.S. population had allergies in the 1950s, while 38 percent had allergies by 1999. Ogren draws an association between these figures and changes in commercial horticulture that began in the 1940s when the USDA recommended growing male plants from cuttings, grafts, and other forms of vegetative reproduction in order to reduce the litter of seeds and fruit falling on public sidewalks. According to Ogren, in the 60s and 70s, when Dutch elm disease wiped out American elms in many cities and towns, the replacement of these iconic street trees was done using male clones on a massive scale. And the trend continues today. The unintended consequence of planting so many male trees is an overabundance of pollen with few female trees to absorb it from the environment. Many other changes have taken place in the environment over the last 60 years, and while the association posited by Ogren is compelling, it is difficult to draw a direct cause and effect from such data. The good news is that the solutions he suggests are neither particularly difficult nor expensive, and do not seem to cause any increased risk of allergies or other unintended health or environmental risks.

Ogren begins by providing background information on OPALS (Ogren Plant Allergy Scale), a system he devised for classifying plants by their potential to create allergies. He explains in lay terms how pollen causes allergies, why the dose of an allergen and the cumulative effects of multiple allergens are important to consider, and how to limit wind-borne pollen and mold spores by planting hedges to block and filter particulates out of the air. Ogren also points out the additional benefits of using plants that are weak allergens—like the seeds and fruit of female plants that attract beneficial birds and pollinators to our gardens.

A short chapter addresses combatting allergies in our neighborhoods and cities. Ogren includes examples of poorly planned plantings around schools and other public places and encourages readers to contact newspapers, landscapers, and nursery owners, and join garden clubs and Master Gardener programs to spread the word about reducing allergens in gardens and public spaces.

The second section, representing the majority of the book, contains a list of allergy fighting plants and the many positive and negative factors taken into account in order to determine each plant’s OPALS score. These scores range from 1, a low-allergen plant, to 10, indicating a plant that causes severe allergies and should probably not be used in most landscapes. Plants are listed in alphabetical order by Latin name, with common names, descriptions, and allergen comments. Although Ogren gardens on the central coast of California, the plant listing covers plants in most USDA climate zones and includes houseplants for those interested in indoor air quality. Good color photographs accompany a few of the ranked plants.

The last pages include a calendar showing the pollen season for dozens of the most common allergenic trees, shrubs, and grasses, a short glossary of botanical terms used in the book, and a reproduction of the USDA plant hardiness zone map.

The Allergy-Fighting Garden is an easy-to-understand, useful guide for those interested in decreasing environmental allergens in their environment. Although he comes off as self-promotional at times, Ogren gives readers the tools to choose plants that will decrease pollen in their own garden and in their community, while decreasing reliance on chemicals and increasing the biodiversity of our cultivated areas.

Josh Schechtel, physician and PHS board member, San Francisco, California