Another option would be a male-sterile tree.

What really brings on my allergy is annual bluegrass and bermuda grass. They are real pollen producers.

Here's a list of trees to avoid:
http://www.aaifnc.org/seasonal_allergy_plants.html
and...

Here is a link that might be useful: list of high pollen and low pollen trees.

The fact is that most trees sold in nurseries have either flowers with both male and female parts or male and female flowers on the same individual plant.

There has been a trend toward "pollenless" tree selections from tree species that have male flowers on separate trees from those with female flowers. Gingko is a good example. And this is where we're just now learning about the problems of ornamental trees that send out pollen without having female trees nearby to act as receptors of that pollen.

Some of the best low pollen trees are the females of dioecious species such as ash, poplar, willow, cedar, juniper, cottonwood, mulberry, xylosma, box elder, podocarpus, holly and smoke tree.

Joe

I'm very sorry to hear about your daughter's allergies.

One thing to keep in mind is that, regardless of what you do with the tree outside her window, the whole plant world is producing pollen and the wind will carry it through her window. Female trees do absorb pollen, but only of the corresponding male species and even one tree would only absorb a small percentage of the pollen in the air.

As a result, I would say it's also important to keep her window closed as much as possible--maybe install a ceiling fan so she can have a breeze without letting pollen inside.

It's easy to tell a female pepper from a male pepper: the females are the only ones to get the red berries.

Thank you to all who posted. I very much appreciate your generous advice. I found a great book by Thomas Ogren who is in San Luis Obispo and was with Cal Poly there. It is Allergy Free Gardening. While I know the landscaping of others will send pollen our way, I hope to do my small bit to help reduce allergies. It is also important that as citizens we ask that our municipalities make the best choices they can by avoiding those landscaping trees that generate tons of allergens and VOCs. Oh, and with Podocarpus, look for the female fruit producing trees, as the male trees are producers of huge amounts of pollen according to Ogden. Thanks again and here's to beautiful landscaping we can all breath easy about!

I heard Mr. Ogren speak on the radio last weekend - he is very knowledgeable. Not all plants produce allegic pollen - he mentioned wind pollination (small white blossoms) the prettier the flower (to attract bugs, birds & bees) the less likely to be allergy exacerbating. He said it is totally possible to landscape municipalities without allergens - it's just not as convenient to do it because of the clean up involved with dioecious female trees.

You can also install a good quality air filter, do some research on which brand/model is most effective. I used to use one and was amazed at how well I slept and how clear my nasal passages were in the morning when it was on.

I also have the book called "Allergy-Free Gardening" by Thomas Ogren. The book is set up like a dictionary or encyclopedia by plant name in alphabetical order and it rates each plant/tree by its allergy potential. It's very helpful. It also mentions which plants may be poisionous, which is helpful for people who have dogs who like to eat berries and parts of plants. From what I remember, the author's website used to allow free searches of plants but it appears that is no longer the case.

You could select a species of tree that is not wind pollinated, which as others mention includes almost all trees with showy flowers. Wind-pollinated plants (including trees) have usually inconspicuous, small flowers and produce a ton of light, wind-borne pollen. They rely on sheer pollen volume and lucky wind currents to carry pollen to the female of the species. Oaks, pines, and many others fall into this category. Many other trees use insects or birds to carry pollen from the male to the female. These trees have conspicuous flowers, produce lots of nectar to attract the animal pollinator, and have heavier, sticky pollen that is not picked up and carried by the wind, therefore cannot cause allergies. Any tree with showy or fragrant (fragrant to attract insects) flowers would fall into this category, and there are lots of them.