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Healthy Garden

Healthy Gardens for Allergy Sufferers

By Stephen ColletteRise Writer
Apr 5, 2019

In my profession, I primarily deal with indoor air quality and health issues that arise inside people’s houses. But what about outside our homes? The outdoor air has a big effect on our health as well. And while we can’t control everything that is in the air outside, we can usually control our own gardens. So as the days turn warmer, and our thoughts follow the sun outside, it’s time to start planning out our gardens

Gardens are our outdoor oases, places we go to connect with nature, feel the dirt between our fingers and toes, tend and care for plants, in our little corner of the earth. Plants generate oxygen and support local species of birds, animals, bugs, and microbiota, and are important components in our local biome. Every spring our first thoughts are that we yearn for these connections to nature.

The second thought we often have the return of pollen allergies, and they hope to get the plants in the garden before allergies knock us down. What if there were a connection? What if we could create a healthier garden?

Girls and Boys

Plants come in two varieties, male and female. Many of us casual gardeners forget about high school biology class when we purchase plants. Depending on your preferences, female plants come with seeds or berries. We will oftentimes avoid purchasing these types of plants because of the mess that they can leave on the driveway or patio when the berries get squashed or the squirrels leave seed pods remnants everywhere. This fact means that we typically purchase male plants, no seeds, no berries, and no mess. The catch? Male plants come with pollen. That pollen needs to be carried by bees, bugs, birds and the wind to the female plants at the right time, for more plants to be created. It really is the birds and the bees in this case!

Photo Credit: The Lung Association

Unfortunately for us, that pollen is the primary cause of outdoor allergies. In fact, pollen triggers over 50 million people’s allergies in the United States every year. Not everyone is reacting specifically to pollen, but it is a major indoor/outdoor contributor for over 8% of the population who were diagnosed with hay fever in 2015. Check out this video to show how much pollen can come from the shaking of one tree!

So in our efforts to create gardens with less mess, we have brought in more pollen-laden plants, impacting our own health. Luckily, there is a solution.


OPALS—not the beautiful stones from central Australia in this case—are the Ogren Plant Allergy Scale created by Thomas Ogren. This scale ranks plants from 1-9 based on their allergenic properties, specifically pollen, but also other elements including the amount of pollen produced, pollen size, length of pollen season, intensity, and whether the plants cause skin reactions. This scale includes all types of plants, including trees, which can be some of the worst pollinators in your yard.

A professional landscape gardener, Ogren has worked and taught in the industry. He became involved in this field over two decades ago because his wife, sisters, and mother all had pollen allergies. With his family suffering, he set out to figure out a solution and came up with this scale as a way of categorizing plant species. Allergists and immunologists backed up the OPALS scale with research supporting its value and rating system. The OPALS scale is widely recognized throughout the world, including by the US Department of Agriculture as well as by the American Lung Association.

How Does It Work?

The scale is pretty straightforward. The lower the number, the less allergenic the plant is, and the better the choice for your gardens. The higher the number, the greater the pollen and allergenic load there is for you and your family. One to three, for example, are typically very low potential to cause allergies. A rating of 4-6 has moderate potential to cause allergies, which can be exacerbated by the overuse of the same plant throughout the garden. A 7-8 OPAL scale rating means that the plants have high potential to cause allergies, so it is advised to plant as little as possible of these types of plants. Finally, plants scoring a 9-10 have an extremely high potential to cause allergies and should be replaced with less allergenic species. 

Some of the worst offenders on the OPAL scale, scoring 10, are Bermuda grass, Queen Anne’s lace, juniper trees, and oak trees. At the opposite end of the scale, some examples of the good plants to have around to reduce allergies are bougainvillea, foxgloves, fir trees, and fan palms. Please keep in mind that whether you have male or female versions of these plants makes a difference. You may be fine with female versions of these plants and trees, so make sure you are choosing the right ones.

Remember that the plants and trees that you purchase are not the only sources of pollen in your yard. Grasses, weeds, existing trees, and bushes can also have high pollen counts. Knowing which plants, weeds, and trees in your region are high pollen emitters means you can weed with more gusto, getting rid of the worst offenders, replace bushes and shrubs over time to help reduce pollen loads, and think about newer trees for your yard in the future. 


Buying and planting low allergy plants and trees in your gardens are excellent, but what do you do about the neighbor’s pollen-laden plants? Although cutting them down may be on your mind—especially if they have 8 or 9 OPALS scale trees and you are an allergy sufferer, we do not recommend such drastic measures. Instead, it is recommended to use physics when planting, and create windscreens with shrubs and bushes. These windscreens will force the wind to move over them, thereby reducing the pollen drop in your yard and around your house. The bushes themselves will also capture pollen, reducing what makes it through to your yard. Again, remember to make sure your hedges are low on the scale, which will provide greater enjoyment of your yard.

Not the Only Decision

Low allergy plants are the first step in making your yard the healthy oasis you have been dreaming about. This is not the only step, however, in completing that vision. You cannot simply choose low OPALS to scale plants from a different climate region and keep them alive with excessive watering and pesticides. An outdoor cactus in Buffalo, New York, for example, is not going to work. Planting local, indigenous plants that require little water allows you to not have to use drinking water to irrigate your landscaping. Also, consider the negative health impact pesticides have on bees and other beneficial insects, birds, and animals that share your wonderful garden. If you do have pests, make sure you are using natural-based solutions to deal with them, instead of the toxic chemicals.

Moving Beyond Your House

Once you have learned more about which plants and trees in your climate region have a low OPALS scale, share the news. Consider what a low allergy planting could do for schools, libraries, and other community and public spaces. Kids desperately need to spend more time outdoors and less time on screens, and making as many outdoor spaces as healthy as possible will help in getting—and keeping—them outside.

Bottom Line

Thomas Ogren has written a great book on the subject titled, The Allergy-Fighting Garden, which is a fantastic resource for those needing some guidance on where to start. Talking to professional landscape architects, gardeners, and garden shops about OPALS plants to add to your garden are the next steps in creating a healthy garden that you can actually enjoy outside—not from inside—your home.

The Allergy-Fighting Garden
Photo Credit: Amazon.com
Disclaimer: This article does not constitute a product endorsement however Rise does reserve the right to recommend relevant products based on the articles content to provide a more comprehensive experience for the reader.Last Modified: 2020-06-23T12:20:40+0000
Stephen Collette

Article by:

Stephen Collette

Stephen Collette is a Building Biologist, Building Science Consultant, LEED Accredited Professional, and a Heritage Professional. Stephen is the owner of Your Healthy House and lives in Lakefield, ON with his wife and 2 daughters.