Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern California Coastal & Inland Valleys
December, 2010
Regional Report

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The hillside at Henry's house is a tangle of plants with no formal plan.

Hillside Gardening

A large portion of Henry's garden is on a steep hillside. The soil is hard like stone, there are two large Monterey pines that have roots growing everywhere, and there is no irrigation. This area presents a bit of a challenge.

Hillside gardening is relevant to many Bay Area residents. The cost of enjoying gorgeous views is landscaping in less than ideal conditions. Anyone who has ever mown a lawn on a steep slope will appreciate the importance of planning your garden for maintenance as well as aesthetic value. If you absolutely, positively have to have a lawn, plant it near the house so that you can enjoy its benefits. And for goodness sake, keep it small!

First Things First
Planning your hillside is very important. At Henry's what we have done over the years is to plant willy-nilly, hoping that something will eventually become established and cover the bare earth. I can't tell you how many packets of forget-me-not seeds I have fed to the birds. We have planted every gift azalea that has presented to the Tenenbaum family. The azaleas are alive, but barely. I have 4 one-gallon containers of vinca waiting to be planted, hoping that the hardy vine will take hold and cover the bare areas.

We shot at least one segment every season on how-to plant on steep slopes for the television show. Unfortunately, we never planted more than one plant for each segment and although they are doing well, "one plant does not a landscape make."

Easy as 1-2-3
Landscaping a hillside can be done several ways; terracing, building retaining walls or simply digging holes and hoping for the best.
Terracing is a dig-and-fill process where you create shallow horizontal trenches, or steps, and use the excess soil to build a berm. Planting is done in the "trench" while the berm helps to retain water and maintain a level grade for the plant.

Retaining walls are expensive to build and require a lot more work initially. Retaining walls can simple, such as boulders used to hold the soil in place, or elaborate hardscape structures. The more construction required, the more expensive the project.

Top and Bottom
The top of a hill is a very special place. Henry and his wife have placed a bench at the top of their garden where they love to sit and enjoy the view. If you can, emphasize the upper reaches of your property with an inviting place to linger. The bottom of the hillside should have as much importance as the top. A patio or a pond will provide a destination.

Here's the Scoop
To plant on a hillside, you must dig a hole large enough so that the root ball of the plant is level with the existing grade. Dig straight down into the slope, stacking the excavated soil in front of the lower section of the hole. This will create a berm. Set the plant into the hole and check that the top 1 inch of soil of the root ball is above the grade. Once you establish that the planting level is correct, go ahead and fill in around the root ball. If your soil is less than ideal, incorporate amendments such as organic compost into the existing soil, but don't add so much that the texture of the backfill is drastically different from the native soil. "Plant a $1 plant in a $10 hole" is good advice when establishing a hillside garden.

Wildflowers may be the answer to planting a large hillside area. Native plants such as ceonothus and mimula are slow to get established but hardy in the long haul.

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