When your garden is flat and your soil is clay, mounds are one of the secrets for successfully growing plants that have evolved to take advantage of California's summer-dry climate.
Soils with a lot of clay are hard to dig in the dry season and get mucky in the wet season, but they can grow a wide variety of plants if you know how to work with them.
In the wild, many drought-tolerant native plants grow on slopes in poor soils. In the garden, the key to making these plants happy is to provide good drainage. Shrubs that are easy to grow if you can provide good drainage include manzanita, ceanothus, silk tassel, toyon, bush mallow, and pink-flowering currant.
To create good drainage with clay soil, you need to make sure any water that falls on the plants does not collect at the root crown. To make sure that rain or irrigation falls away from the plant, the most well-known technique is to plant the root crown of each plant slightly above the level of the soil.
A more effective technique is to build mounds. For a row of plants or a garden bed, make the mounds as long as the row or as wide as the garden bed, and at least a foot high.
The mounds can be made of the same clay soil, ideally transferred from other parts of your yard. If your landscape includes any hardscape that needs to be excavated, you can relocate soil on site instead of paying to have it trucked away. Or if you want a vegetable garden, use the clay soil for your native mounds, and buy a truckload of compost and topsoil for the vegetables.
After you plant the native shrubs, add 2 to 4 inches of mulch to help suppress weeds, moderate soil temperatures, shelter the worms that work the soil, reduce water needs, and give the landscape a neat, finished look. Be sure to pull the mulch a few inches away from the root crowns of each plant so that water does not collect there.
And don't forget that most drought-resistant plants take two to three years to become established, so they will need water for the first summer or two. While they are growing roots, they may not seem to be growing much above ground. The best place to water them is at the drip line (at the outermost circle formed by the branches), not near the root crown. Finally, if the plants appear to be wilted, water the leaves, not the roots.
A public garden where you can see native plants flourishing on mounds is Native Hill at Foothill College in Los Altos Hills, next to Parking Lot 5-A (bring 8 quarters for parking).
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manzanita, ceanothus, silk tassel, toyon, bush mallow, pink-flowering currant
© 2005 Tanya Kucak