Xeriscaping Can Save Water
The Puget Sound area may sprout slugs and clouds for eight months of the year, but from May to August we average about the same rainfall as Arizona's Sonoran Desert.
In the past, Northwest gardeners coped with yearly drought by trundling out hoses and sprinklers, or installing automatic irrigation systems. But rapid and continuing population growth has placed increasing strains on regional water sources, and it's likely that the water available for home gardening will become both more scarce and more expensive in coming years.
These factors explain why growing numbers of local gardeners are taking to xeriscaping, a new gardening approach stressing plants and gardening techniques that require little or no irrigation.
Xeriscaping (the term derives from the Greek word, xeros, meaning dry) was developed in 1981 by the Denver Water Department to promote water conservation, and the concept has spread rapidly throughout the water-hungry West. Communities in California, Nevada and Texas promote xeriscaping and Los Angeles began to mandate it for new commercial, industrial and multifamily landscape installations in 1988.
``Designing landscapes for the Puget Sound area that don't waste water is ecologically sound, and saves time and money, too,'' says Howard Stenn, a xeriscaper who has been developing a large border of drought-tolerant plants for three years at the Seattle Tilth Association, the nonprofit gardening organization in Seattle's Wallingford district.
``Many plants that are drought tolerant also are low maintenance and pest and disease resistant,'' Stenn adds. ``That makes xeriscaping even more attractive.''
Stenn designed his drought-tolerant bed at Tilth's demonstration gardens as a mixed border of low-maintenance evergreens, herbs and flowering plants that would look good all year and require virtually no watering once they were established.
Stenn planted rosemarys, lavenders, santolinas and rues (Ruta graveolens) for year-round structure, and added coral bells (Huechera sanguinea), mulleins (Verbascum spp.), yarrows (Achillea spp.), carnations and coneflowers (Echinacea purpurea) for seasonal blooms. Camomile, chives, fennel and several varieties of thyme and sage also have also been tucked into pockets along the border.
Last summer, Stenn watered only the newly established plants and left the rest of the border to benign neglect - a state in which it flourished beautifully. ``The border was planned to be a mix of use and beauty. We filled it with the kinds of tough plants that anyone can grow well in this area,'' he says.
Xeriscaping is based on the following principles:
Start with a good design. Terrace or contour slopes to retain runoff from rainwater efficiently. Establish thirsty plants at the base of slopes, where they receive maximum runoff. Place plants with similar water requirements together for maximum watering efficiency. Grow vegetables and cutting flowers in raised beds to reduce water use. Most drought-tolerant plants require well-draining soil, so if you have heavy clay soils, amend them and berm or mound your improved beds to encourage good drainage.
Improve the soil. Adding organic matter to soil boosts its moisture-holding abilities. Even the heavy clay soils that many of us garden in will retain water more efficiently for root growth if they are improved with organic soil amendments. Compost - chopped leaves, shredded fir bark, hay, manure, grass clippings - should be tilled into the soil in fall and left to ``settle in'' over the winter. If you use sawdust or other nitrogen-robbing materials, remember to add nitrogen to the soil. Home gardeners should consider adding 1 pound of nitrogen per 25 square feet of mulch, or consulting a mulch supplier.
Do use mulch. Seventy-five percent of rainfall evaporates or runs off from bare earth, but almost all of this rainfall is retained by mulched earth. A mulch two to four inches deep keeps earth and plant roots cool, and also helps suppress weeds. Combinations of bark, hay, clippings and fine gravel can serve as mulches, which should always be kept several inches away from the woody stems of plants. Because many of the small drought-tolerant shrubs, such as rosemarys and lavenders, are native to the arid Mediterranean region, Ciscoe Morris, Seattle University grounds department supervisor, recommends mulching only lightly around them, to prevent soggy roots and rot.
Limit lawn areas. Replace high-maintenance, thirsty turf with drought-tolerant ground cover and ornamental grasses. Some recommended ground covers: ajuga, English ivy, hypericum, thyme, vinca, pachysandra and hostas. Ornamental grasses include pampas grass, blue fescues, yuccas and liriopes.
Choose low-water plants. Many xeriscapers recommend using only native plants in the landscape, theorizing they are best suited to a region's natural cycles of rainfall and drought. But other xeriscapers encourage use of drought-tolerant, nonnative plants, especially ornamental herbs and small shrubs such as rosemary, thyme, sage and lavender. Recent tests in California show these hardy exotics actually tolerate prolonged dry spells better than most native California plants. Additional recommended drought-tolerant plants:
- Small shrubs - rockroses (Cistus spp.), brooms (Cytisus spp.), genistas, potentillas, winged euonymus (Euonymus alata), daphnes.
- Perennials - eryngiums, armerias, dianthus, sedums, poppies, coreopsis, and rudbekias.
- Annuals - calendulas, nasturtiums, portulaca
Irrigate efficiently. Whether you use hoses or automatic sprinkler or drip systems, the key is to irrigate slowly, so that water penetrates the soil surface instead of running off as waste. Infrequent, deep watering encourages deeper root growth than frequent, shallow watering. Irrigating in the morning reduces evaporation, as well as the spread of fungus.
Practice good maintenance. Most drought-tolerant plants don't like to be fertilized (overfertilizing makes them prone to disease) and require only touch-up pruning. Other than watering newly established plants, the xeriscaper's major maintenance task is weeding, because weeds compete with desirable plants for available moisture and nutrition.
For further information:
- The Elisabeth C. Miller Horticultural Library at the Center for Urban Horticulture (3501 N.E. 41st St., Seattle, 543-8616) carries pamphlets, articles and other sources of information on xeriscaping.
- The King County Cooperative Extension offers a free bulletin by George Pinyuh entitled KC 125 - Low Water Use Plants. It can be ordered by calling 296-3986. Or you can talk with a master gardener Monday through Friday from 10 to 4, 296-3440, about any gardening topic including xeriscaping, composting and mulching.
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