Gardening in the Wet and the Dry
BY Kali Robson, Ph.D.
Gardening with Drought Tolerant Natives
When people think of the climate in the Pacific Northwest they think, Wet! In reality, many of our native plants are quite drought tolerant. In this part of the world we usually get lots of rain in the late fall, winter, and early spring, when plants are dormant and needing little water. In the summer and early fall we typically have about two months of drought and many of our native species are well adapted to these conditions. In many parts of eastern North America, summer rain, thunderstorms (and tornadoes!) are far more common during the summer months.
If you have a sunny, dry place in your yard, planting drought tolerant species is a far better strategy than using plants with high water needs. With ever more crowded conditions in the northwest, clean water is becoming scarce and the need to conserve water supplies is urgent. The impending extinction of salmon and other aquatic species means we can no longer waste water to maintain a lawn. Summer water rationing is common in many parts of the Pacific Northwest, and will probably become more restrictive in the near future. Keep this in mind, gardeners, and plant your yards accordingly – choose the right plants for the soils and climate.
Species tolerant of dry shade under large trees such as Douglas fir (Pseudotsuga menziesii) include sword fern (Polystichum munitum), salal (Gaultheria shallon), Cascade Oregon grape (Mahonia/Berberis nervosa), and vine maple (Acer circinatum).
Many conifers such as ponderosa pine (Pinus ponderosa) and incense cedar (Calocedrus decurrens) prefer sunny dry sites. Madrone (Arbutus menziesii, beautiful, but difficult), oceanspray (Holodiscus discolor), Oregon myrtle or California laurel (Umbellularia californica) are also tolerant of summer drought. Good old snowberry (Symphoricarpos albus) is tolerant of dry to fairly wet conditions, and sun to part shade.
Kinnikinnick (Arctostaphylos uva-ursi) is a great plant for erosion control on dry, sunny banks but is a bit slow to establish. Other species of Arctostaphylos are beautiful and drought-tolerant, but more difficult to grow. Smooth sumac (Rhus glabra) can take dry, sunny conditions and provide spectacular fall color, but will develop many suckers if the roots are frequently disturbed. Creeping Oregon grape (Mahonia/Berberis repens), tall Oregon grape (M./B. aquifolium), mock-orange (Philadelphus lewisii), baldhip rose (Rosa gymnocarpa) and Western serviceberry (Amelanchier alnifolia) are also excellent choices for dry, mostly sunny areas. There are also many drought-tolerant flowering perennials that will do well in a dry meadow or rock garden, including species of Penstemon, stonecrop (Sedum spp.), blue flax (Linum perenne) and yarrow (Achillea millefolium).
Native Plants for Wet Areas
Most plants other than wetlands species, are unable to tolerate saturated soils for any length of time. This is because the amounts of oxygen in soggy soils are so low that the plant's roots literally drown and become unable to function. Although green plants do produce molecular oxygen as a byproduct of photosynthesis, they take some of it back during respiration – they must respire, just as we must. However, wet soils are not an uncommon feature in many areas of the Pacific Northwest and there are many native plants that are quite able to tolerate such conditions.
Trees that can handle wet soil include Oregon ash (Fraxinus latifolia), Western red cedar (Thuja plicata), good, old red alder (Alnus rubra, a nitrogen fixer) and black cottonwood (Populus trichocarpa/P. balsamifera), as well as Sitka spruce (Picea sitchensis), though it may have pest problems. Shore pine (Pinus contorta var. contorta), Pacific crabapple (Malus/Pyrus fusca) species of willow, especially Pacific willow (Salix lasiandra) and Sitka willow (S. sitchensis) are also good choices, but don't plant cottonwoods or willows near sewer lines or drain fields.
For sunny wet areas with shallow water there are, of course, emergent plants such as the aggressive cattails (Typha latifolia) and many species of rushes and sedges. Shrubs tolerant of similar conditions include Western spirea or hardhack (Spiraea douglasii), Nootka rose (Rosa nutkana), clustered wild rose (Rosa pisocarpa), salmonberry (Rubus spectabilis), and red twig dogwood (Cornus sericea/C. stolonifera). Perennials include yellow monkey flower (Mimulus guttatus).
For boggy, shady sites try under-utilized species such as skunk cabbage (Lysichiton americanum), black twinberry (Lonicera involucrata), devil's club (Oplopanax horridus), yellow stream violets (Viola glabella), Pacific bleeding-heart (Dicentra formosa), and sylvan goatsbeard (Aruncus sylvester). Many native ferns will do well, including lady fern (Athyrium filix-femina) and Northern maidenhair (Adiantum pedatum/A. aleuticum). For the gardener who finds fussier species worth trying, there are plants such as Labrador tea (Ledum groenlandicum).
This is just a sample. There are many more you can read about in the following references:
- Editors of Sunset. 1988 Sunset Western Garden Book. Lane Publishing Co., Menlo Park, CA.
- Editors of Sunset. 1998 Sunset Western Garden Book. Sunset Publishing Co., Menlo Park, CA.
- Leigh, M. 1995 Grow Your Own Native Landscape. Wash. St. Univ. Cooperative Extension, Thurston Co.
- McNeilan, Jan. The Pacific Northwest Gardener's Book of Lists. Dallas, TX, Taylor Publishing Co., 1997.
- Pojar, Jim., MacKinnon, Andy eds. Plants of the Pacific Northwest Coast. Vancouver, B.C., Lone Pine Publishing, 1994.
Kali Robson is the Coordinator for the new Watershed Stewardship Program with WSU Extension in Clark County. She also teaches part-time for the WSUV branch campus and for Master Gardeners training. Kali is also Proprietor & Botanist for Nothing But Northwest Natives Nursery & Robson Botanical Consultants. She's always happy to give seminars on gardening with native plants and to welcome visitors to the retail/wholesale nursery operated by husband Tom Henn, located in Battle Ground!
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