Because of our wacky topography and developers' drive to build on every possible inch of usable space, California's subdivisions are cut into and out of hillsides, leaving us some pretty challenging slopes to deal with.

Invariably the homeowner's request is for a ground cover. I always chuckle. An old nursery friend of mine heard that question so many times that eventually he blurted out to a surprised customer, "Lady, every plant covers the ground!"

My friend was right; every plant does cover the ground. So I challenge the request, gently asking, "What would you say if I told you that you can plant about anything on a slope, it doesn't need to be a ground cover?"

Once I get their attention, I explain that slopes are simply gardens set at an angle. True, you have to be careful about how you irrigate them, and not all plants are suited for slopes, but many are.

Typically, the concern -- which is a reasonable worry -- is to anchor the hillside so it doesn't erode or wash away. The best plants for that purpose are those that make deep roots, like trees and shrubs.

Native trees and shrubs are ideal: California lilac (Ceanothus), toyon (Heteromeles arbutifolia) and oak trees (Quercus), for instance. Plant them in combinations and you create habitat that attracts birds and other wonderful wildlife.

I also advise homeowners on what to avoid: eucalyptus trees because of their shallow roots and brittle branches. I've seen big eucalyptus branches fall on the top of cars and huge eucalyptus lying in the middle of boulevards, having blown over in a strong storm.

Avoid ice plant, especially the Hottentots fig (Carpobrotus edulis). This succulent is most often planted on a slope all by itself, with the intent that it form a massive, uniform carpet.

The problem is, as it ages, the stems die out underneath while more and more succulent leaves form on top. Eventually, the mass grows so heavy that it literally slides down the hill, taking most of the soil and hillside with it. In addition, Hottentot fig is one of our most problematic invasive plants.

And speaking of massive, uniform carpets, avoid planting just a single type of plant on a slope or anywhere else. That uniform look never works. As one of the plants dies or weeds blow in, what shows up are the flaws, not the plants.

So don't fall for that ground cover trap. Select diverse plants that make beautiful gardens and stable hillsides.

Nan Sterman is author of "California Gardener's Guide Volume II." She is a gardening expert, communicator and designer who has long grown an organic garden of plants that both feed her family and beautify her garden.