But when managing slopes, it's most important -- more crucial than the plants you choose -- to pay attention and watch where water goes, Wilson says. "The idea is not to stop it, but to slow it down."
Small rills and gullies can be managed with simple debris dams or retaining walls -- and by altering irrigation habits. But if a sizable slope is in danger of slippage, it's time for professional help. Major problems demand serious, sometimes costly, remediation -- performed by competent experts.
Above all, Radtke says, to protect property and people there must be a cooperative approach among homeowners and between public agencies. Our soils are all interconnected, and what happens on one slope, in good weather and bad, affects adjacent properties.
His hillside development, which backs into Topanga State Park, is about to lose its best ally. He's trying to retire and is leaving his home of 30-plus years for the flats.
But before he goes, Radtke wants to assemble and educate the people in houses above and below his own. Most, he suspects, have never met.
"Neighbors need to work together and watch out for each other," he says.
Lili Singer can be reached at firstname.lastname@example.org.