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 Allergists, landscapers and horticultural workers have few resources
to recognize and recommend plants to people with particular
allergies, so the Landscape Allergen Working Group of the American
Academy of Allergy, Asthma and Immunology (AAAI) created a guide to
help.
"We had a number of requests about what the appropriate plants are,
and there were conflicting stories online at the time," said senior
study author Dr. Warren Filley, a recently retired staff allergist
at Oklahoma Allergy and Asthma Clinic in Oklahoma City.
"Patients always want to know if what is in their yard is causing
the problem, and it can be more complicated than that," he told
Reuters Health by email.
Plants at nurseries or gardening centers aren't labeled as
allergenic, and they usually don't include mention of toxicity,
invasiveness or other hazards either, he added. The workgroup formed
to address this issue, including experts in allergy, occupational
health, aerobiology and botany from research centers across the
country and the Centers for Disease Control and Prevention.
Filley and colleagues focused on plants with a low pollen yield by
first looking at the way their pollen is dispersed. Mosses and
ferns, for instance, spread spores through the air, though typically
in small amounts over limited areas. On the other hand, conifers and
flowering plants tend to produce large quantities of pollen with
high concentrations that can travel across a region.
In particular, gymnosperms - plants that have naked seeds visible to
the eye and not enclosed in fruit - can spread a large amount of
pollen by air. Pine, spruce, fir and juniper conifers may create
allergic reactions in some patients, the workgroup writes in the
Journal of Allergy and Clinical Immunology: In Practice.
Flowering plants, or angiosperms that produce seeds in a fruit,
often require insects to disseminate pollen. These could include
coneflowers, tiger lilies, azaleas, orchids, sunflowers and more. In
general, landscaping should use plants with showy, insect-pollinated
flowers to reduce allergies in the environment, they write.
People with certain allergies should also consider possible
cross-reactions, for example those with ragweed allergy may also
react to alder, and those sensitive to juniper pollen may also react
to olive trees.
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"As always is the case with humans, there is a great variability in
what each person is allergic to and can or cannot tolerate," Filley
said. "There is no such thing as an allergy-free garden, but
individualization with the help of your allergist and a landscape
professional can help."
The guide suggests first determining whether a plant has
insect-pollinated flowers, then whether it is invasive or toxic, and
then whether it is appropriate for your location based on its
hardiness score and your climate.
In many urban environments, cities have increased allergies by
planting ornamental trees with high pollen spread, including maple,
sweetgum, pine, beech, aspen, poplar, fir, white oak and sycamore. A
low-allergenic landscape could include more dogwoods, magnolias and
tulip poplars, the group says, as well as female plants that don't
spread pollen by air and a broad diversity of plants that don't
cross-react.
Landscapers should also consider other allergens, such as grasses
that may cause reactions during mowing or rain, as well as plants
with thorns, sap, bark and leaves that cause skin reactions.
At the same time, eliminating many popular plants entirely can be
unrealistic, said Paloma Carinanos Gonzalez, a botanist at the
University of Granada in Spain who wasn't involved in the AAAI
guide. Urban environments also have low biodiversity, monocultures,
spontaneous plants and pollution interactions that can increase
allergies, she noted.
An Index of Allergenicity of Urban Green Spaces that Carinanos
Gonzalez created considers the allergic risk of a green space
according to the species that grow there. More than 350 species are
now in the index, most which are compatible with Mediterranean
climate conditions, though it is being expanded to other Spanish and
European locations.
"Knowing the plants that cause allergy can help you improve your
condition and quality of life, generating healthy landscapes and
environments with low allergen risk," she said by email.
SOURCE: https://bit.ly/2vNzVe8 Journal of Allergy and Clinical
Immunology: In Practice, online August 7, 2018.
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