Gardeners always have to worry about the grade and contours of the landscape, but with a steep garden those concerns become crucial. A poorly landscaped garden hillside can erode quickly, either through continual weathering or as a sudden slide after a violent storm. Before you even begin to select your plants, stabilize your hillside through prudent planting and solid hardscape.
Erosion Control Planting
Without the right plants, it's very difficult to stabilize a steep slope in a garden. Forget about turfgrass, as it can easily wash away if it is planted on a steep slope. Instead, incorporate a variety of plants with deep roots, capable of holding the soil. Plant groundcover plants such as Franciscan Manzanita, small woody plants such as sage, shrubs such as brickell bush and trees such as coastal live oak. Match your plants to the soil type, water and temperature conditions of your garden.
A garden on an ungraded hillside is a nightmare to plant and maintain. Make your life easier by dividing your garden into terraces. Scoop out level areas of the hill and use the dirt to extend the ledge out to divide the hill into a series of steps. Construct small retaining walls two feet or less in height to hold the terraces in place and prevent erosion. Extend the walls slightly above the soil surface and mulch your garden beds to minimize splash erosion and runoff. Construct a stairway between the different levels of your garden to make it easy to plant, maintain and enjoy your garden beds.
For a lower-maintenance, erosion-proof garden, create a container garden on a hardscape foundation. Build a broad concrete stairway down the steep slope from a terrace at the top to one at the bottom. Place planters at both sides and in the center of each step to concrete three strips of vegetation running down the hill. Plant the top and bottom terraces with flowers, herbs, veggies or whatever else you want.
Alternately, build a concrete ramp crisscrossing the hill. At each corner where it zigs, create a flat landing with a raised flower bed and a place to sit. Build a railing next to the concrete ramp and place small pots with flowers along the side of the ramp.
A steep garden provides an excellent setting for a waterfall. Build the waterfall out of flat rocks embedded into concrete to minimize erosion. Landscape the waterfall so that it flows along the side of the stairway or path leading down from the top of the garden. For a modern look, create a channel in the middle of your staircase and run a continuous stream of water down a section of the stairway.