When Matthew Johnson talks about legumes at this week's monthly meeting of The Gardeners of Tucson, he won't focus on lentils, beans, peas or other veggie-garden crops.

Instead, he'll discuss popular and new species of landscape legumes. Familiar plants include mesquite, ironwood, acacia, Texas ebony and palo verde trees; shrubs such as bird of paradise, senna and fairy duster; and flowers like bluebonnet and dahlia.

They all are identified by the trademark fruit pod that hangs from the stem.

"Legumes are the real workhorse of dry landscapes," Johnson said in an interview.

"Within Arizona, the material we have available provides an incredible, diverse palette of shape and form," he says. They include colorful flowers and fruit pods, whose ripe and dried seeds from some species are edible.

There are many natives in the Sonoran Desert, its climate a prime habitat for them. "Seasonally hot, dry climates with summer rainfall tend to have a lot of legumes," Johnson says.

The best time to plant legumes is in warm weather, which means almost any time of the year in these parts, he says. Be mindful about cold-hardiness, as several species go dormant or die back in frosty weather.

Consider two crucial issues when planting, he advises: location and irrigation.

"Make sure the plant is going to be appropriate to the place where it's going," he says. Legume trees can grow quite large and can lift hardscapes in order to spread roots.

Even native transplants should get frequent watering until they are well-established. For trees, that requires a deep soaking as well as watering beyond the tree trunk to reach spreading roots.

Natives can be weaned off supplemental irrigation after they're established.

Johnson's talk on Tuesday will include legumes that are coming into the landscape market. While not readily available in Tucson, he'll mention two to watch for:

• Trinity tree (Caesalpinia paraguariensis). Introduced by a Phoenix nursery, this South American species sheds its green-tan bark like a eucalyptus. Its rust-colored canopy pops in a spring garden. Clusters of yellow flowers support oval, black-brown seed pods. Some local nurseries can order them.

• Sonoran catclaw tree (Acacia occidentalis). This very large tree has puffball-type flowers. Bees favor its papery pods for producing honey. Desert Survivors nursery occasionally has it.

Johnson names the velvet mesquite as his favorite native legume. "It really says 'Tucson,' " he says.

If you go

• What: "Landscaping With Legumes," a talk by Matthew Johnson, director of the University of Arizona's Desert Legume Program.

• Where: The Gardeners of Tucson meeting, Tucson Ward 6 council office, 3202 E. First St.

• When: 7 p.m. Tuesday.

• Information: 322-0830, www.gardenersoftucson.org

Contact local freelance writer Elena Acoba at acoba@dakotacom.net