Arbor Day just passed, and we are now full on into allergy season. I hope that anyone who recently bought and planted a tree did a little prior research. Had I had been a smarter gardener years ago, I would have first researched the trees I planted more thoroughly. I did look at the estimated height, plant zone, and the sun and water requirements, but I didn't check the potential for pollen. That mistake has cost me a lot of sneezing, coughing and itchy eyes.
Trees do not usually produce pollen year-round, but spring is often a good time to check for it. Fruit, seeds or seed pods are indicators of a female tree. Female trees do not produce pollen. The cotton-like clusters that fly in our Solano wind are seed masses from cottonwood trees or native coyote brush. They are not pollen. That attribute belongs to male trees.
Pollen comes in an array of colors, not just the yellow as seen with acacias. Green, red, purple, white, brown, and gray pollen are all common. Another clue to male gender (and the potential for future pollen) is the adjective “fruitless” on the tree label. It's fruitless, because it is male. Fruitless mulberry and fruitless olive produce a lot of pollen. Still another indicator to check is a distinctive bulge at the base of a landscape tree indicating it has been grafted. Trees planted by cities are usually male (and pollen-producing) because the city doesn't want fruitsplatting on the sidewalks or roadways that they have to keep clean and safe for walking.
Some trees are monoecious, meaning that the tree has both genders on the same plant. If you don't want pollen, don't buy it. Some junipers and some palms are monoecious. Check with the nursery owner first to determine if the tree you are considering buying will produce any pollen.
A good resource to check before considering any potential pollen-producer is The Allergy-Fighting Garden by Thomas Leo Ogren (Ten Speed Press, 2015).
The American College of Allergy, Asthma, & Immunology has a useful website with allergy offenders, when they are most prevalent and tips on gardening when you have allergies:
https://acaai.org/allergies/management-treatment/living-with-allergies/gardening-with-allergies/
PollenLibrary.com runs an allergy and botany library with 1200 plants that can be researched by plant name or by ZIP code for allergen potential. The same site has a map with current allergens, allergy forecasts and allergy alerts at Pollen.com.
https://www.pollenlibrary.com/
Our bodies have evolved to recognize pollen as foreign invaders, just like COVID, cancer cells, bacteria and the common cold. Now, we just have to be smarter in what we choose to plant.