In the Garden:
Aloe flowers are pollinated by creatures and rank as a low-allergen plant according to the OPALS system.
Xeriscape Part III: Plant Selection: Low-Allergen Gardening
Xeriscape design includes a set of seven principles to guide you in the creation and long-term maintenance of a colorful, earth-friendly landscape that suits your unique needs. Previous reports covered design, site analysis, whether to install turf, and plant selection basics. Because there are so many terrific desert plants available, my next few reports will cover some selection criteria to consider as you hone your preferred plant list.
Remember when people suffering with respiratory issues came to the Southwest for relief? That cure is long gone, with frequent bad air quality days in many of our urban areas. According to the Centers for Disease Control and Prevention, National Center for Health Statistics, in 2010, 25 million adults and children were diagnosed with hay fever, a common name for pollen allergies. Many of us have or know a child with asthma, a respiratory condition that is made worse by airborne pollen. If you or your family members don't suffer from these problems now, that doesn't mean you are safe indefinitely. It is fairly common to develop an allergy over time as exposure to pollen increases. The following strategies can help you create a low-allergen garden and reduce exposure, at least from your own yard.
Choose plants that are pollinated by creatures rather than the wind. How can you tell? Typically, brightly colored or fragrant blossoms attract bees, birds, bats, moths and other insect pollinators. Such flowers produce sticky or bumpy pollen grains that attach to the mobile pollinator, who transfers it to the next flower it visits. Sticky pollen is less likely to become airborne and inhaled.
In comparison, wind-pollinated plants have drab flowers, usually white or pale greenish-yellow, hanging in thin clusters an inch or two long. Wind-pollination is less precise than a foraging pollinator, so these plants increase their reproductive chances by generating enormous quantities of pollen. The grains are small, lightweight and nonsticky, allowing them to remain aloft in the Southwest's windy climate. These characteristics also enable this type of pollen to be easily inhaled.
Choose well-adapted plants for your area and maintain them properly. Stressed plants produce far more than their normal pollen count, because they are trying to reproduce before they die.
Add many different plant species to your landscape, rather than repeating the same species in quantity. This reduces repeated exposure to a particular pollen.
Some plant species have male-only plants with male (pollen bearing) flowers and female-only plants with female (fruit bearing) flowers. A desire by homeowners and municipalities to avoid cleaning up so-called messy fruit drop of female plants led to the propagation and transplanting of male-only plants in large numbers. The health costs of increased quantities of pollen were not factored into the equation decades ago.
The following common desert landscape plants are considered high-allergen producers according to author Thomas Ogren, in Allergy-Free Gardening: The Revolutionary Guide to Healthy Landscaping (Ten Speed Press, 2000):
Arizona ash (male) (Fraxinus velutina)
Arizona cypress (Cupressus arizonica)
Canyon ragweed or giant bursage (Ambrosia ambrosioides)
Common or improved Bermuda grass. (Sterile vegetative hybrid Bermuda does not produce flowers or pollen.)
Fruitless mulberry (male) (Morus alba)
Hop bush (Dodonaea viscosa)
Italian cypress (Cupressus sempervirens)
Juniper (male) (Juniperus sp.)
Mesquite (Prosopis sp.)
Fruiting olive (Olea europaea) (Pollenless named varieties are available, such as 'Swan Hill' olive.)
Saltbush (Atriplex sp.)
Sumac (Rhus sp.)
Triangleleaf bursage (Ambrosia deltoidea)
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