About 20 years ago, my friend Kathleen and I sat shoulder to shoulder, our backs to the sun as we surveyed the small plot of land in front of my house. As we discussed soil conditions, color, shape, and location, Kathleen deftly sketched out a plan for my new garden.
Sex — or plant sex anyway — wasn’t on our minds back then, but according to horticulturist, allergy researcher, and author Thomas Leo Ogren, it should have been. While trees of any sex may be clean air superheroes, it is the non-pollen producing females that wield allergy fighting super powers.
In his 2015 book, The Allergy-Fighting Garden (Ten Speed Press), Ogren explains that when it comes to producing pollen, the most troublesome of allergens, male plants, shrubs, and trees are the main culprits. Ideally, given the tie between allergies and asthma, female chauvinism is definitely in order when planning our gardens.
Unfortunately, the chauvinism often goes the other way. Because city planners often view them as less “messy” than fruit-producing female trees, male trees are often nurtured in urban environments while their female counterparts are often weeded out when they are seedlings. This “unnatural selection” Ogren writes,
“… has taken a large toll on females and has left us with ever more urban pollen, because female plants not only produce no pollen themselves, but they also trap and remove pollen from the air.”
While we can’t directly control the man-made pollutants that come our way, we can decrease natural pollutants on our home turf by adding a plant’s allergenic properties to our list of criteria when landscaping our yards. Doing so can even help reduce the amount of particulates in our immediate environment. As Ogren told me in a recent email interview,
“An allergy free garden has very little pollen drifting around. Manmade pollution attaches to airborne pollen and makes the pollen much more allergenic. Allergy-free plants trap and remove manmade pollutants from the air but they do not shed pollen, so they don’t give those same pollutants back to us.”
In fact, Ogren devotes a whole chapter of his book to allergy-blocking hedges. The ideal hedge is not only healthy, attractive, easy to grow and fairly fast growing, he writes, but
“A tall hedge planted on the side of your property, one that will act as a wind block, will also catch, trap, and stop a great deal of pollen, mold spores, dust and other allergenic particulates from coming into your yard.”
In addition to helping readers understand the facts of life in the plant world, Ogren’s book contains an A to Z list of what he refers to as “allergy-fighting plants.” His self-named allergy scale — Ogren Plant Allergy Scale or OPALS — ranks each listed plant based on the following factors:
- The amount of pollen produced, if any
- The potency of the pollen
- How much of the year the plant is in bloom
- The size of the actual pollen grains
- The specific gravity of the pollen grains
- How sticky or dry the grains are
- Whether the tree is perfect-flowered (male and female parts in the same flower), monoecious (separate male and female flowers growing on the same plant), dioecious (plants are totally separate-sexed), or polygamous (perfect-flowered and single-sexed flowers on the same plant)
- Whether the sap causes dermatitis
- Whether the smell of the flowers bothers people
Ogren admits that most gardeners and landscapers are not aware of his rating system and says that you won’t often find OPALS tags on plants at most nurseries. After lecturing on this topic for 15 years, however, he says that some consciousness is starting to seep into the garden world, and it is definitely worth asking about when choosing plants for your yard.
Using allergy-fighting plants in your own garden and demanding that they be used in urban landscaping is just one more way to help alleviate the health impacts of climate change. As Ogren told me,
“We need to plant more plants that are: insect-resistant, drought-tolerant, non-invasive, pollinator-friendly, and of course, allergy and asthma-friendly as well. Climate change is already causing lots of problems for those with allergies and asthma, and if we don’t make some real changes soon in how we approach this….life could become just flat out miserable for them…and that just isn’t fair at all. Every one of us in this country should have the right to breathe.”