Crusader Tom Ogren named his latest book Safe Sex in the Garden and Other Propositions for an Allergy-Free World to get our attention and "shake people up." Ogren, a horticulturist, writer, teacher and landscaper from California, wants to spread the word that urban and residential landscapes are making lot of people very sick because there are too many male plants—and too much pollen. If your eyes itch and your nose runs every summer, or if you suffer from asthma, you'll want to read this book and its companion, Allergy-Free Gardening.

In the plant world, males produce pollen (the equivalent of semen in male animals). Pollen grains are so tiny and light that they pass right through window screens. Every seed-producing plant, from the tiniest flower to the tallest tree, has pollen-producing stamens and egg-containing pistils so that pollination can happen. Some species have stamens and pistils in separate flowers (that is, some flowers are male and others females), and other species bear separate male and female flowers on completely different plants. For instance, hollies are either male or female, so at least two of them have to be planted to get the pretty berries. Unlike animals, male and female plants look the same overall. You can't tell gender until the plant blooms.

Female plants and trees produce seeds, messy pods, or squishy fruits that have to be raked away or swept up, so they have long been considered undesirable for yards and streets. Male plants, which shed only tiny grains of pollen and insignificant male flower parts, are considered much more practical. Horticulturists have figured out how to develop "male clones" and nurseries are full of cultivars advertised as "low maintenance" or "seedless." (A cultivar is a cultivated variety propagated asexually by grafting). Our towns and yards are full of male clones. Ogren, the crusader, claims "massive numbers of people are getting sick and thousands are dying for the cause of tidy sidewalks," and in Safe Sex he spells out the ties between plant gender and human health.

There are more people with pollen allergies now, and urbanites are most susceptible. If our cityscapes and yards had better gender diversity, more of the pollen shed by the males would be trapped by the females. He offers the surprising explanation that the male and female parts of plants emit opposite electrical charges; female plants' negatively charged (and sticky) pistils attract and collect airborne grains of positively-charged pollen. Humans are negatively charged, and the problem today, Ogren says, is that with female plants becoming rarer, pollen is ending up on the linings of our noses and throats.

Ogren says allergy sufferers can find relief by making changes right in their yards. A juniper beneath a bedroom window can expose a person to 10 times the pollen that comes from a juniper down the street.

What about our town? Moscow has a tree inventory, a database of 114 species. Cultivar names are specified, but not always. Most were planted for easier upkeep and less "mess" on sidewalks--like male green ashes. But many trees here have male and female flowers on the same tree, like lindens and black locusts, so pollen doesn't travel far to reach a receptive female. And Moscow has some all-female green ashes, too. I visited Roger Blanchard, at City Parks, and we compared the trees along our streets with Ogren's recommendations. It's not easy to look up plant gender! Often several books have to be consulted. Roger likes North American Landscape Trees by Arthur Jacobson, because the names are accurate, and because gender is specified.

Ogren has rated more than 1,000 plants in a scale he has invented called OPALS (Ogren Plant Allergy Scale) and in his book Allergy-Free Gardening, and on his Web site, www.allergyfree-gardening.com, he provides tips for selecting better plants for allergy sufferers. Interesting stuff!