Residential, commercial and public landscapes-including our schools-are loaded with male-only trees and shrubs, since these are a litter-free and therefore low-maintenance choice. But propagating our urban forests with male clones is a mistake not only because males are the pollen-producers, but because the lack of female plants to absorb the pollen has sent allergenic pollen counts skyhigh nationwide. Horticulturist Thomas Leo Ogren covers this and other allergy-related topics.