If you think “waterless garden” and picture a stark xeriscape filled with spiky succulents, it’s time to flip the stereotype. Two gardens in Tacoma and Puyallup are living proof that you can have a lush landscape without anything but rainwater — even as our Northwest summers get hotter and drier.
Here are two stories of turning drought into abundance.
The rain garden
It’s ironic, but rain gardens are also proving excellent at drought tolerance, thanks to research by Rita Hummel, a scientist at Washington State University’s horticulture extension in Puyallup. Five years ago, Hummel planted 16 rain gardens on the sunny edge of the facility’s parking lot as part of a retrofitting process. Three plant designs — all turf, mixed shrubs and trees, and all evergreens — plus an empty control garden were replicated four times, with the same kind of initial depression, drainage and soil. The plants were watered in the summers of 2010 and 2011, and haven’t seen anything but rainwater since.
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The result? Thick, lush groves with brilliant palettes of color and texture, so dense the weeds don’t stand a chance.
“I tell people to think of rain gardens as a landscape bed,” says Hummel, looking proudly over hers. “And the fact that these look as good as they do, (with) our summers so dry... .”
Rain gardens aren’t a new idea. Hummel is part of a drive to encourage Puget Sounders to plant 12,000 of them by the end of 2016. A rain garden is essentially a way to manage stormwater on-site, collecting runoff in a depression and using plants and microorganisms in the soil to filter toxins, rather than letting it all wash into drains and Puget Sound.
For gardeners, though, it’s also a way to deal with potential wet spots in winter, such as low terrain or downspout exit points.
Hummel’s main purpose with her 16-rain-garden experiment was to determine which cultivars did best in the three zones of a rain garden: the wet center, the dry edges and the transition zones around the sides. Most previous research, she says, has been done on the East Coast, where summers see more rainfall than in the Northwest. Here, plants have to deal with increasing rainfall and storm events in winter plus near-drought in summer.
So Hummel chose native and drought-tolerant plants, including ninebark, Oregon grape, dogwood, beargrass and wax myrtle. But she also chose nonnatives popular with landscape designers, like variegated willow. And she threw in some trees chosen for their beauty and drought-tolerance: a hardy swamp magnolia, madrona, the Mediterranean strawberry tree, even a bald cypress.
Astonishingly, almost everything thrived. Hummel didn’t find much difference between the burgundy East Coast “Centerglow” ninebark (a rain garden staple) and the lime-green Pacific ninebark. Both shrubs fill her gardens with leafy foliage and flowerheads. The Northwest native beargrass grew just as well as more standard grasses, adding a thin, silvery texture. The Oregon grape bursts with enormous, blueberry-sized fruit, and the willow spreads its reddish-white spires like a Broadway star. Lower to the ground, red osier dogwood runs rampant with both deep green and gold leaves.
The only surprise was the salal — a Northwest native that just couldn’t take the intense heat last summer. And just one swamp magnolia beat the heat — Hummel credits the slight morning shade of the wall behind it.
Of course, the waterless success of a rain garden depends on more than its plants. Digging the depressions, Hummel also installed some drainage channels (extra-deep rivulets with stones or gravel) to avoid winter waterlogging. The soil is a specified bioretention mixture of 60 percent compost and 40 percent sand. And the gardens are heavily mulched with bark chips — important to minimize evaporation. Plants also need water for their first two or three summers. Planting thickly helps reduce the drying effect of wind, as well as weeds that compete for water.
But the takeaway for Northwest gardeners is that rain gardens don’t just hold water in winter — they also thrive without it in summer.
The backyard woodland
Bill Hagens had two reasons for wanting a waterless garden: to save water and stop mowing his lawn.
“I hated cutting the grass,” says Hagens, who owns a house with his wife, Noel, in Tacoma’s North End. “And we’re better off here than most of the world with water, but why waste it? We don’t know where we’ll be in the future.”
So the Hagens set a goal: Replant their entire front and back lawns with a woodland landscape that was pretty but didn’t need any water. At all.
Three years later, with the help of Gardensphere Nursery, they’ve done it — almost. In the backyard, beds meander between crushed rock pathways (for water retention) filled with healthy plants in a silver-green-purple-pink palette. Tall spires of fuzzy gray Jerusalem sage contrast with spouting “Prairie Blues” grass and frilly burgundy heuchera. Tall vine maples play backdrop to pink Echinacea, lavender and hardy lilac geranium. White creeping hemlock gives a splash of feathery white-green.
The only thing the Hagens is still watering are three new white birch trees and a scatter of sword ferns between them, just for this summer. After that, the only plants that will need water are the blueberries and some potted annuals.
Around the front, things are more challenging. The shaded house bed of salal, ferns and nandina is doing fine, and the elfin thyme lawn is thick and fuzzy. On the terraced beds, though, there are gaps between succulents and evergreens, and between the yuccas and lamb’s ears on the parking strip.
“I haven’t figured it out yet,” Hagens says.
But he’s thrilled with the maintenance: no mowing, hardly any pruning, not much weeding and mulching maybe once a year.
And of course, no watering.
The secret? Good soil, good mulch and the right plant choice.
“For years I was out here watering the grass,” says Hagens. “I just love this.”
Waterless garden tips
Want a truly waterless garden? Take these tips:
▪ Start with the soil. Thoroughly remove weeds and grass, and replace with biorentention mix (ideally 60 percent compost and 40 percent sand).
▪ If you are building a rain garden, consult ext100.wsu.edu/raingarden for drainage and digging techniques.
▪ Choose the right plants. Natives and drought-tolerant nonnatives are best (avoid invasives), but still consider shade and wind conditions. See ext100.wsu.edu/raingarden for a list of good rain garden plants; see tinyurl.com/zcz7nlg for a list of drought-tolerant Northwest plants.
▪ Plant in fall so the new plants get established in the rainy season.
▪ Pile on organic mulch such as G&B organic soil conditioner. Reapply yearly.
▪ Water regularly and deeply for the first two or three summers. Keep it weeded.