By Nicholas Ditzler

It’s a cliché that men are more aggressive by nature and women are more nurturing, but it appears that cliché is playing out in the plant world. And it’s impacting countless people with pollen allergies.

Male plants produce and disperse the millions of pollen particles that cause constant coughing and sneezing while female plants remove pollen from the air, says Thomas Leo Ogren, a horticulturalist and allergy researcher who has investigated the relationship between plants, pollen and allergies for decades.

“For years, male plants and trees were preferred because they produce no seeds, pods or fruit – but of course they produce huge amounts of pollen,” Ogren says. “Where there are no female plants in the landscape, the pollen has nowhere to go.”

As people with seasonal allergies know, pollen can limit one’s ability to spend time outside and care for a garden or yard. Removing male plants and introducing female ones around the home can decrease the amount of pollen a person comes into contact with when outside, Ogren says in his book The Allergy-Fighting Garden, published in 2015.

Ogren developed a scale called OPALS (Ogren Plant Allergy Scale) that ranks more than 3,000 plants from 1 to 10 based on how allergenic they are. Examples of plants that are allergy friendly include pansies, impatiens and snapdragons. The scale details how much pollen each plant produces and how severe allergy patients can expect their symptoms will be.

With climate change affecting pollen production, greater amounts of carbon dioxide are triggering much larger blooms of pollen, Ogren adds. This causes certain trees that are common in urban areas, such as male junipers, to bloom twice in each season; in the past they bloomed once a year.

“This means the selection of allergy-friendly plants is more important now than ever,” Ogren says.