Credit: Alex Manders / Getty ImagesKey PointsSeasonal allergies are primarily caused by trees and grasses, whose tiny pollen particles travel on the wind.Low-allergen flowering shrubs can add low-maintenance color and interest to gardens.Plants with colorful or fragrant blooms attract insects for pollination, and are less likely to affect allergies.Summer flowers add a welcome pop of color to your garden, but this time of year can also bring on …