If you're one of the 50 million-plus Americans affected by seasonal allergies, your yard and garden may be sources of misery.

Non-Showy Flowers Among Worst Pollen-Producing Culprits

Microscopic pollen contains the male cells of flowering plants. Pollen can have a smooth surface, but the real nostril tweakers are the barbed ones that latch onto your sinus membranes and don't let go. These tend to come from flowers that are small and unattractive. "Flowers that are not really showy tend to be pollen producers," says master gardener Pam Geisel. Because they're not attractive to bee pollinators, they have had to evolve to the barbed form in order to be wind pollinated and carried off into the air.

Ornamental grasses are some of the most popular landscape plants because they're so versatile. But if you have pollen allergies, you may want to steer clear of them. "Grasses are probably the worst pollen producers," says Pam. Their flowers bloom for a long period of time and are grown over a large area. Even lawn grasses like Bermuda and annual bluegrass can be terrible on allergies, unless you mow frequently to minimize flowering.

Many communities plant non-fruiting male trees so they don't have to deal with messy fruit-producing female trees. The olive tree (pictured below) is popular in many landscapes, and because of its beautiful structure, many homeowners plant one in their garden close to their house and windows. The olive tree's barbed pollen, however, makes it one of the worst pollen producers.