Are Male Trees Making Trouble?

Richard Primack

“There is absolutely no common sense; it is common nonsense.”  Henry David Thoreau in Reform Papers.  

For several decades, Tom Ogren, a horticulturist from California, has claimed that the worsening problems of allergy across the USA are due to government officials planting only male trees in cities.  In his view, “botanical sexism” has led to city trees producing an excessive amount of pollen with disastrous consequences for people suffering from allergies. 

As pointed out in a recent article in the Boston Globe, his theory is actually almost entirely wrong. 

First of all, many common city trees, such as lindens, Norway maples, oaks, birches, and flowering pears, do not have separate male and female plants. 

Oak trees are commonly planted as street trees, but do not have separate male and female plants.

Second, for species with separate male and female trees, such as some maples, ashes, junipers, and sassafras, government officials don’t just plant male trees as he claims. 

Thirdly, many common street trees, such as cherry trees, flowering pears, and crabapples, are insect pollinated, and don’t contribute to allergy problems. 

Flowering pear trees are insect pollinated, and don’t contribute to allergy problems. 

Finally, Ogren claims that planting more female trees would reduce pollen in the air because the female flowers would capture the pollen from the air. This is not tree, as the stigmas of the female flowers of wind-pollinated trees, such as oaks, probably only capture less than one in a million of the pollen grains released into the air.  

So while Ogren’s ideas are dramatic and lurid, they lack common sense. 

This article was published in the Boston Globe as: The theory of ‘botanical sexism,’ or 
planting ‘male’ instead of ‘female’ trees, debunked 
By Mike Damiano