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You go outside on a gorgeous summer day eager to tidy up the garden when all of a sudden, the sneezing, runny nose starts. Ahh, pollen! With asthma being the number one chronic disease for children, and science now pointing to a direct link in allergies causing asthma, what’s a gardener to do?

Well, first off it helps to understand why rates of asthma and allergies have been increasing every year. Part of the answer is we don’t like messy things. As the costs to propagate trees and shrubs over the years have come down, this means gardeners and municipalities now have more access to male plants that don’t produce seeds, fruits or seedpods (i.e. all the stuff that ends up on the sidewalk). The only problem with that is that since they’re not producing all those things, they produce pollen instead. Depending on the variety of tree or shrub, this can mean massive amounts of pollen and without the female nearby to grab that pollen out of the air your handy pollen collector (i.e. mucous membranes in your nose) do that job and voilà! Allergies. So, while our streets and yards are now cleaner, the amount of pollen in our air has gone way up.
Side note: It wasn’t all propagations fault, there was also a pesky Dutch Elm Disease that wiped out millions of trees across the United States in the ’60s and ’70s. These trees just so happened to be female, and when they were replaced guess who was chosen in their place, that’s right- mostly male trees!

At least it is only bad for a few days, right? Not quite. Some trees can release pollen for months, not days, and even with trees that release pollen for only a week or two, there is so much of it that it covers everything and can get blown around by winds over a large area for an extended period. Pollen can blow over hundreds of miles, settle, and then get blown around some more. Part of what makes a plant more or less allergenic is the distance the pollen was designed to travel for that specific plant. The plants that need the pollen to travel further tend to be more allergenic than those that only need their pollen to travel a few feet.

 


Pollen from a Cedar tree

 

We know overexposure to massive amounts of pollen is bad, so what can we do if we are allergy-prone? Should we rip out every plant in our garden and only plant females? Should we call in the gravel truck? And what about that Juniper hedge that my neighbor has? Part of the solution is knowing which plants are producing pollen and how much. To help us out, there is a handy rating system called OPALS which stands for Ogren Plant Allergy Scale System. It gives a 1-10 rating for each plant with one being the least allergenic to 10 being the most.

The first step is to determine what plants are in your garden and what is producing the pollen. If you discover plants that are high on the OPAL rating, you can decide if it is worth it to remove them and plant something else. If you are starting a new landscape or replacing old plants, make sure to verify that the new plants are low-to-no pollen producers. Typically, if you see a plant in your garden that has a berry, fruit or seedpod it is a female and so doesn’t produce pollen. Coincidently, If you are trying to attract wildlife such as birds, bees and butterflies, male trees and shrubs do not provide fruits or nectar for these animals and so adding more plants that produce edible fruits is a win-win for wildlife and your garden!

 


Female yew with berries

 

Well, that’s all fine and well but what about all the pollen coming from the neighbors? If there is room, it may be a good idea to plant a fast-growing, low-to-no pollen hedge on the windward side of your property. The denser and faster it grows, the better. Also layering of different plants will help block some pollen as well. It is recommended to hose down your hedge a couple of times a year to rinse off the pollen and also remove other air pollution build-up.

Some plants, depending on the time of year, are hard to sex and so plant identification will help. I encourage you to either hire a landscape designer familiar with designing an allergy minimizing garden or check out a copy of The Allergy-Fighting Garden by Thomas Leo Ogren, which goes into great detail on everything discussed in this article so far and it is also where you can find some of the most common landscape plants organized alphabetically and rated on the OPALS Scale.

 

Here is a quick reference for some allergy-friendly plants to use and those to be avoided:

The Good The Bad
Agapanthus Alder
Azaleas Arborvitae
Bamboo Birch
Boxwood Cypress
Clematis Elm
Columbine Fescue grass
Dogwood Junipers (male)
Flowering fruit trees (e.g. Apple, Pear, and Plum) Oak
Geranium Poplar trees
Hibiscus Podocarpus
Hydrangea Privet
Ilex Willow (male)
Iris Yews (male)
Juniperus ‘Witchita Blue’  
Magnolia  
Myrica penslyvanica  
Myrica californica  
Ribes alpinum  
Yews with visible small red berries  
Viburnum  
Violets