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...