For allergy sufferers, a lot of the focus is on weeds and garden plants that create their hay fever symptoms, but the pollen of trees is often a more serious cause. There's not much you can do about trees grown by your neighbors or planted by the city in parks and other public areas, but you may be able to reduce your hay fever symptoms by choosing trees and shrubs for your own yard that are either entirely free of allergy-causing pollen (hypoallergenic), or selecting those with pollen that is heavy and coarse, unlikely to drift around on wind currents to exacerbate your allergy symptoms.
The presence or non-presence of pollen in a tree is a matter of the tree's sexual reproduction method, a process that involves its flowers and pollen. Normally, a tree produces seeds only when the pollen from male flowers reaches female flowers, a process known as pollination. This can happen through the action of bees and other insects that transfer the pollen from flower to flower as they feed on nectar; or the pollen can drift from flower to flower on air currents.
A tree's flowers can be either male or female, and only the male flowers will produce pollen. Some trees are monoecious, meaning that individual trees produce both male and female flowers. Other trees are known as dioecious, meaning that an individual tree will have either male or female flowers, but not both.
Thus, with a dioecious tree species, it is possible to plant a female tree that produces no pollen whatsoever, since the flowers are all female. Some examples of trees where you can plant a non-pollen-producing female tree include:
- Acer rubrum 'October Glory’
- Aspen (Populus tremuloides), cottonwood, poplar, and related trees
- Boxelder (Acer negundo)
- Cedar (Cedrus spp.)
- Juniper (Juniperus virginiana)
- Maidenhair (Ginkgo biloba)
- Mulberry (Morus ssp.)
- Swamp tupelo (Nyssa sylvatica)
- White ash, green ash, etc. (Fraxinus spp.)
- Yew (Taxus spp.)
In some cases, nurseries may carry only the female trees, making your choice an easy one. With other species, though, you may need to specify that you want a female tree that produces no pollen.
But while all female dioecious trees will be pollen-free, they aren't all great landscape choices. For example, just because a female Ginkgo biloba gives off no pollen, that doesn't make it an ideal yard tree. Ginko trees shed a fruit-like product that makes them among the messiest trees that you can grow.
Some monoecious trees that produce pollen are actually fairly good choices for allergy sufferers since their pollen is heavy and coarse, unlikely to drift on the wind and cause allergy symptoms. After all, the pollen of monoecious trees needs to be transported only a short distance to a female flower on the same tree, a task that can be rather easily accomplished by insect pollination. Examples of monoecious plants with coarser pollen include:
- Crabapple (Malus spp.)
- Dogwood (Cornus spp.)
- Fir (Abies spp.)
- Flowering cherries and plums (Prunus spp.)
- Magnolia (Magnolia spp.)
- Eastern redbud (Cercis canadensis)
- Spruce (Picea spp.)
- Tulip tree (Liriodendron tulipifera)
- Ornamental pear (Pyrus calleryana )
The Bottom Line
If you are an allergy sufferer, planting either female monoecious tree species or a dioecious tree species known to have heavy, coarse pollen, may reduce your hay fever symptoms. By combining this with shrewd choices for garden plants and careful weed control, you may find that growing seasons are much more enjoyable.