In the past, many of our streets were lined with trees such as our native elms, which shed very little pollen. We've replaced many of these trees with trees that have both male and female flowers ("monoecious") or with male plants (the source of pollen) because they're "litter-free" i.e. they don't produce seeds or seedpods. (Female plants produce no pollen.) Norway maples and London plane trees are two of the common monoecious culprits.

Another problem is that there is so little diversity in the trees we plant that people are constantly exposed to just a few kinds of pollen--a recipe for creating allergies.

Some of the trees and shrubs recommended for planting instead include a diversity of trees and shrubs including these natives: tulip poplar (Liriodendron tulipifera), hawthorn (Craetaegus), mountain ash (Sorbus americana), and serviceberry (Amelanchier).

And we could plant more female trees of these varieties: junipers (Juniperus virginiana), yews (Taxus canadensis), red maple (Acer rubrum), tupulo (Nyssa sylvatica), and sassafras (Sassafras albidum).