As the emerald ash borer continues to kill ash trees and different diseases and pests threaten others, homeowners may wonder what is left to plant.

The good news from Jeff Iles, chairman of the horticulture department at Iowa State University, Ames, is that there is lots left.

Iles will bring his message to Clinton on Saturday, March 3, when he will be the keynote speaker at the 28th annual Horticulture in the Heartland seminar at Clinton Community College.

The day-long event also features a choice of four breakout sessions, lunch and a garden shop. It is sponsored by Clinton Trees Forever, Bickelhaupt Arboretum, Clinton Community College and the Master Gardeners of Iowa State University Extension-Clinton County.

Iles' first tree-planting advice is a caution about maples.

A variety called "Autumn Blaze" has been widely planted in both new subdivisions and older neighborhoods and anytime a plant becomes prevalent, there is the risk that if it becomes the target of a new disease or pest, a sizeable portion of the landscape could be wiped out, he said.

So diversity is the key. Here are four of his suggestions.

• Ginkgo, or ginkgo biloba.

Although this isn't a native tree and doesn't offer much food for insects, it is long-lived, has few disease or pest problems and displays a beautiful yellow color in the fall. Look for the male ginkgo, as the female produces fruits that many find foul-smelling.

• Kentucky coffee tree, or gymnocladus dioicus.

This is a native tree with few disease or pest problems. Again, homeowners may want to look for the male tree as the female produces pods that some people consider a maintenance issue, Iles said.

Two cultivars to look for are "Espresso" and "Stately Manor."

• Bald cypress, or taxodium distichum.

Yes, this is the same tree that produces "knees" — or knobby projections above its roots — when growing in the swamps of the southeastern United States.

In the Midwest, it is "very, very tough and has very few problems," Iles said.

It is a conifer that turns a brilliant copper color in the fall before shedding its leaves. It is not native.

Black gum, or Nyssa sylvatica.

This is a native tree with "a nice branching structure and nice fall color, a reddish orange that stands out in the landscape," Iles said.

Hybridizers are consistently adding new cultivars, including those that are a little more narrow and upright so that they fit better in urban landscapes, he said.

As for understory trees, Iles recommends fungus-resistant crabapples and the Japanese tree lilac.

While homeowners also may have heard about various problems affecting oak trees, Iles said he wouldn't shy away from planting them.

"Oaks in general are a fantastic tree," he said. Good varieties include bur, white and swamp white oak. Again, hybrids are being created; "Regal Prince" is a cultivar he would recommend.

As always, it is important to match a tree to its site.