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Thomas Leo Ogren


One single grain of pollen…nothing you’d want in your eyes or up your nose.

Thirty years ago I got with my horticulture students one day and we conducted our very first “sniff tests.” We sniffed some pansy flowers and nothing happened. We all sniffed some double dianthus flowers and nothing happened. Then we sniffed some bright red bottlebrush flowers (Callistemon) and wow! The third fellow to sniff the flowers sneezed so hard it almost scared us. Everyone laughed, finding it pretty darn funny.

But by the time we’d gone through the whole class, one third of them were sneezing…and some of them were still sneezing four days later. I had just learned something very important about flowers and allergies; some plants trigger allergies, and some do not.

Bottlebrush flowers

Now I’d always heard that big, pretty flowers don’t cause allergies, but the bottlebrush flowers were large and beautiful. Some thirty years later I’m still researching the connections between allergies and what we plant in our yards, parks, schools, and gardens.

Along the way I also discovered that a huge number of trees and shrubs that are sold in nurseries are single-sexed clonal male plants. These are often preferred because males don’t make any seeds; they’re sold as “litter-free” plants. The downside, and it’s a big one, is that males produce pollen, lots of it! In some cities more than half the trees and shrubs are now these all-male clones, and the result has been an epidemic of allergy, and asthma.

Many palm trees are also all male or all female. The female palms produce seeds but no pollen, the males though, they produce plenty of pollen.  In this photo below is one cluster of flowers from a male palm tree…starting to shed its pollen.

One of the most common street trees in many cities is the ash tree (Fraxinus.) Virtually 100% of those sold are grafted male trees. Ash trees are related to olive trees (in the family Oleaceae) and the pollen from both of them is quite allergenic. An allergy to either ash or olive pollen (or to their relative the privet bush) can trigger a dozen different food allergies AND a very dangerous allergy to latex as well.

In the colder winter parts of the US and also in Europe and Canada, yews (Taxus spp.) are common and popular landscape plants. All of the yews are separate-sexed, and most sold are males. Yews are poisonous plants and from them is made Taxol, a chemo therapy drug used for breast cancer. People who get over-exposed to the profuse pollen from nearby male yews can and do come down with symptoms that may mimic chemo treatments. The female yews though, like ALL female plants, are 100% pollen-free. The plant below is a female yew, and if you can find one like it, buy it and plant it in your own landscape. Not only will it not produce any pollen ever, it will also trap any incoming pollen from nearby male yews. Female yews are true allergy-fighting plants.

What can you do?
It is often claimed that pollen can blow in for hundreds of miles away and that there’s nothing much you can do to avoid it except to stay in your house. It isn’t true, not at all. Most pollen from a tree or shrub will fall out and land within 20-50 feet of the tree itself.  If it is a big highly allergenic tree and it’s in your own yard, you and your children will all be exposed to it, over and over again. The name for this is proximity pollinosis; the closer you are to the source, the greater will be your exposure and your symptoms.

The best, safest thing you can do is to remove the most allergenic plants from your yards and replace them with pollen-free female plants.

The landscape plants that are used in schoolyards should always be allergy-free, but often they are the very opposite. The highest official pollen count ever recorded in the US was taken from the roof of the administration building at an elementary school. Of some 24 large mature trees at this school, on inspection it was found that 23 of the 24 were clonal males. All parents, teachers, PTA members and good citizens should be very concerned about the kind of plants used where our small children go to study and play. Please visit the site of this non-profit devoted to healthy school yards,

For more advice and to find out where to buy female plants, go to the website of the non-profit group, The Society for Allergy Friendly Environmental (SAFE) Gardening. ( )

For more advice on which landscape plants are allergenic and which are allergy-fighting and allergy-friendly, check out my latest book, The Allergy-Fighting Garden. You can find it in bookstores or online. See:

About Thomas Leo Ogren: He has an MS degree in Agriculture/Horticulture, and is the author of eight books and hundreds of articles about health and gardening. His work has appeared in the London Times, The New Scientist, The Chicago Tribune, the New York Times, and many other fine publications.

Posted March 13, 2015

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