Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern California Coastal & Inland Valleys
September, 2007
Regional Report

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More color, less work is our mantra for Henry's hillside.

Henry's Hillside

We have a large expanse of hillside in Henry's garden in San Mateo that is a challenging area to landscape. For one thing, the soil is nonexistent. Henry bought the house when he first moved here from D.C. because it was built on rock and not prone to earthquake damage. Good for houses, bad for gardens. The Monterey pines are infested with pitch canker and are not long for this world. Anything we plant under them will lose the protective canopy in the next few years.

The hillside itself is steep and faces southwest. In other words, it gets really hot in the afternoon, which normally wouldn't be a problem but since we have rock instead of soil, plants tend to suffer unless the irrigation system is up to snuff.

Henry's wife loves color and so our first priority is to keep Mrs. Henry happy. She actually paid someone to dig six large planting holes in the rock hard earth for us. We have taken advantage of two of them, planting a creeping bottle brush (Calistemon) to act as a ground cover. I wanted to plant ferns and rhododendrons, but was out-voted.

Tackling a Slope
Planting on a hillside involves some serious excavation if you want your plants to survive through the rainy season. The top of the rootball must be above the grade of the slope so that water doesn't collect and rot the roots. We built a moat around the low side of the planting hole, kept the rootball high in the soil, and let nature do the rest.

Watering a hillside is a challenge, especially in rocky soil. Water causes erosion as it runs downhill, which can be controlled by installing drainage pipes, terracing, installing baffles, or planting low-growing shrubs to break the force of falling rain. With good planning and thick planting, you can channel the water and make it work for you. It's important to have a diverse collection of plants that have different root depths. A mixture of trees, shrubs, and perennials planted closely together will stabilize an otherwise slippery slope.

Terracing is an expensive option. The base of the terrace wall will have to withstand a tremendous load. All this geometry is best handled by professional landscape contractors. But think how lovely it would be to have a secluded patio area on the hill with inviting paths leading up to it; why the view alone would be worth the cost of the installation!

I have been trying to encourage gaura, annual lupines, and Japanese anemones to run wild on the hill, but the rock doesn't seem to welcome scattered seeds. My next step will be to gather a collection of perennials in 4-inch pots from the San Francisco Botanical Garden plant sale and plant them in the fall, just before the rain begins. I plan to work just a small section at a time to save my back and to see how the plants survive their first winter. Besides, removing all the weeds and digging all those holes may compromise the integrity of the hillside.

Every garden has its own set of challenges, some more difficult than others. The hill at Henry's will bloom, eventually. Now if I can only get Henry and Buzz out there with picks and shovels, my job will be a breeze!

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