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Planting the Seeds for Allergy Free Landscaping

Posted on Mar 29, 2022 in:
  • Built Green

Selecting low-allergy, female species of plants for your garden can help mitigate allergies exasperated by increased pollen counts from climate change.

Young man blowing his nose outdoors

Spring is upon us in the Pacific Northwest and for many it also marks the beginning of allergy season, which affects up to 30% of the US population and 40% of US children. The CDC expects that climate change will lead to both higher pollen concentrations and longer pollen seasons. However, climate change is not the only contributing factor to the increase in pollen counts, it is only exasperating a situation caused by generations of selective breeding and prejudicial landscaping decisions.

All plants contain male sex organs called stamens and female sex organs called pistils. Pollen is dispersed from male stamens and captured by the female pistil to create seeds for germination. While most plant species are monoecious and include both male and female reproductive organs, many plant species are dioecious with individuals that make only pollen or only seeds. In fact, most of the tree species used for street trees in urban settings are male dioecious trees.   

The Allergy-Fighting Garden by Thomas Leo Ogren

Tom Ogren, author of The Allergy-Free Garden, blames most of the allergy inducing problems on selectively only landscaping with male plants. He explains that male species of shrubs, trees, and flowers produce pollen and other air particles. “It all has to do with sex and the need to plant female plants.” Female trees were thought to produce unattractive and unwelcome litter in the form of fruit, seeds, flowers, cones, pods, and cotton. Since the 1970’s, city planners and landscaping crews began planting male trees to reduce cleanup costs and efforts. Ogren states, "I was able to trace it to the fact that many street trees that were planted years ago have finally reached maturity. And those trees are all male and now overloading the air with pollen." With this increased demand for male trees, horticulturalists began selectively breeding and cloning more and more dioecious male plant species, moving beyond trees into shrubs and flowers. Increasing more and more pollen-only producing varieties and species to fill the landscapes that surround us.

Ironically, if city planners and landscapers had prioritized female trees and plants, in the same way as male plants, neither pollen nor unwanted seeds or fruit would cause issues. Female plants do not produce fruits or seeds if there are no males of the same species within 20 to 30 feet from its roots. He goes on to explain that allergy-reducing landscaping includes not just understanding the importance of plant sex, but also encouraging pollinators and eliminating mold growth that can occur in hedges and compost piles.

From his observations Ogren now believes that the reason so many butterflies are disappearing is because the [female] nectar-producing trees were a major food source. "And they are disappearing because they are being replaced by the [male] pollen-producing trees," said Ogren. Planting native species of plants supports native pollinators with the foods they are accustomed to. Furthermore, non-native plants may become stressed since they are not used to the climate, and therefore, may produce more pollen. To guide cities to plant less allergenic trees, Ogren developed the Ogren Plant Allergy Scale (OPALS). The scale rates plants from 1–10 based on their allergy potential.

Grass is a major pollen producer, thus, to reduce allergy triggering pollen, the Asthma Society recommends mowing grasses regularly before it flowers. Better Home and Gardens recommends planting species that are pollinated by bees; the pollen of these species is heavier and sticky and therefore stays on the bees rather than floating around in the air. In addition, mold growth in hedges and compost can also affect allergies. To discourage mold spores Ogren recommends keeping hedges trimmed regularly to increase air flow between the branches, keeping compost bins covered, and turning compost piles about every 2 to 4 weeks.

Local pollen counts can be tracked and monitored through the US Air Quality Index. The University of Illinois Extension recommends reducing exposure to plants that flare up allergens through wearing long sleeved shirts, long pants, gloves, hat, and even a mask while gardening.

Seattle Area Pollen Seasons

Increases in carbon emissions and climatic changes in weather patterns are causing more people around the world to experience negative health effects from pollen and other outdoor allergens. According to the CDC, individuals with preexisting respiratory illnesses such as asthma, are more sensitive to pollen, which has been linked to increases in asthma attacks and associated medical costs that exceed $3 billion every year.  Decreasing the plants that contribute more pollen into the air can increase quality of life, especially for those already living in urban low-quality air zones.

The following is Allergic Living’s list of low-allergy options for your garden:

Flowering Plants

Shrubs/Bushes/Herbs

Lathyrus odoratus – Sweet pea

Coleus blumei – Coleus

Catharanthus roseus – Periwinkle

Hosta – Hosta, plantain lily

Digitalis – Foxglove

Physalis – Chinese lantern

Impatiens – Impatiens

Sempervivum – Hens and chicks

Myosotis – Forget-me-nots

Hydrangea grandiflora – Big leaf hydrangea

Nierembergia – Cup flower

Viburnum – Viburnum shrubs, highbush cranberry, nannyberry

Petunia – Petunia

Heuchera – Coral bells (many varieties)

Viola – Johnny jump up, pansy, violet

Teucrium crispum – Wood sage

Brodiaea – Elephant’s ears

Physocarpus opulifolius – Dart’s gold, ninebark

Crocus – Spring-flowering crocus

Bergenia – Elephant’s ears

Cyclamen – Cyclamen

Kolkwitzia amabilis – Beauty bush

Galanthus – Snowdrops*

Aronia melanocarpa – Black chokeberry

Gladiolus – Gladiolus

Rodgersia pinnata – Featherleaf rodgersia

Hyacinth – Hyacinth (numerous varieties)

Helianthemum – Sunrose, rock rose

Gentiana – Gentian

Gaura – Gaura, beeblossom

Geranium – True geranium, cranesbill

Vaccinium corymbosum – Blueberry bush

Hemerocallis – Day lily

Berberis vulgaris – Barberry bush

Peony – Peony

Daphne – Daphne

Polemonium – Jacob’s ladder

Nandina domestica – Nandina

Rhododendron – Azalea, rhododendron

Salvia greggii – Autumn sage

Fuchsia – Fuchsia

Salvia clevelandii – Cleaveland sage, blue sage

Dianthus – Carnation, pinks

Trees

Papaver – Poppy

Stick to female trees, which may drop berries or seeds but don’t produce pollen

Begonia – Fibrous or tuberous begonia

Persimmon – persimmon tree

Rosa – Rose (avoid high-scent varieties)

Amelanchier lamarkii – juneberry tree*

Phlox – Phlox*

Vines/Climbing Plants

Iris – Iris

Thunbergia alata – Black-eyed Susan vine

Erythrocoma triflora – Prairie smoke

 

Kniphofia – Red Hot Poker

 

Clematis – Clematis

 

Tulipa gesneriana – Tulip (bulbs may irritate sensitive skin)

 

Penstemon – Beardtongue

 

Antirrhinum – Snapdragon

 

Asclepias tuberosa – Butterfly weed

 

Hibiscus – hibiscus

 

Narcissus – Daffodil

 

Bulbine frutescens – bulbine

 

*Pictured below

Amelanchier lamarkii – Juneberry tree

Amelanchier lamarkii – Juneberry tree

Galanthus – Snowdrops

Galanthus – Snowdrops

Phlox - Purple

Purple phlox

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