The maritime Pacific Northwest is generally not known for being sunny and dry. Perhaps this is due to the fact that the region, encompassing southwestern British Columbia, western Washington, and northwestern Oregon, has an annual average of more than 225 cloudy days and 150 days with measurable precipitation. Although the climate is designated as oceanic or marine West Coast (with moderate rainfall), there is a distinct mediterranean-like dry period during the summer, when there may be no rain for weeks on end, usually from early July through early September. Gardeners who prefer to reduce the time and expense of watering need to know which plants to choose for drought tolerance.
Great Plant Picks (GPP), an educational program of the Elisabeth C Miller Botanical Garden in Seattle, Washington, has been assembling a comprehensive palette of outstanding plants tailored for plant enthusiasts who live west of the Cascade Mountains, between Eugene, Oregon and Vancouver, British Columbia. The list includes almost 800 trees, shrubs, perennials, bulbs, and vines, many of which withstand the dry conditions of maritime Pacific Northwest summers with no supplemental irrigation. Many urban and suburban gardens lack shade; more than a third of the GPP selections thrive in full sun and are drought tolerant. Gardeners will find a wide assortment of suitable plants on the list that will shine in one or more seasons and thrive under both of these growing conditions.
Mahonia xmedia is a superb shrub for wintertime interest, with several cultivars to choose from, including ‘Charity’ and ‘Winter Sun’. They make excellent specimen plants with their statuesque form and dramatic, pinnately compound leaves in whorls along coarsely branched stems. Large racemes of soft yellow flowers begin to appear in January and are much prized by hummingbirds. I was forced to move a mahonia in July last year, and most of the soil fell off the roots; the plant never missed a beat, but kept right on growing after replanting—a sign of a truly sturdy shrub!
Conifers are attractive year-round but are especially important during winter as they provide an evergreen, forest-like element to the garden. Grand fir (Abies grandis), incense cedar (Calocedrus decurrens), shore pine (Pinus contorta var. contorta), and Western hemlock (Tsuga mertensiana) are Northwest native conifers that do exceedingly well in full sun and tolerate our dry summers. Use them as specimens or plant them in groups to create a woodland. There are also a number of exotic conifers well adapted to these same conditions, including: a selection of Spanish fir (Abies pinsapo ‘Glauca’) with striking, frosty blue needles; Serbian spruce (Picea omorika), which has dark green needles with silver-blue undersides; and a cultivar of limber pine (Pinus flexilis ‘Vanderwolf’s Pyramid’), which is a new GPP for 2011, chosen for its pyramidal shape and twisted silvery blue green needles. Any of these would bring structure, texture, and color to the winter garden.
Bursting forth with a flourish of color in late winter and then disappearing until the following year, early flowering bulbs are highly prized for heralding the coming spring. Many prefer to be kept dry during their summer dormancy. The captivating goblet-shaped flowers of Crocus tommasinianus range from pale silvery lavender to dark purple. For those weary of March’s gray skies, few plants can match the radiant color of the large, golden trumpets of Narcissus ‘King Alfred’, the slightly more diminutive N. ‘February Gold’ with golden yellow flowers, or the canary yellow of N. ‘Saint Keverne’. Plant all of these bulbs in drifts for a wonderland of glowing flowers.
“No matter how long the winter, spring is sure to follow,” states an old proverb. Trees, shrubs, and perennials dress up their spring foliage with all colors of the rainbow. Crabapples are exceptional flowering trees for springtime, with a bonus of colorful fruit in the autumn. The GPP tree committee has chosen five that are dependably disease resistant. Malus ‘Strawberry Parfait’ is a heavy bloomer and one of the best pink-flowered cultivars. ‘Adirondack’ offers profuse crimson buds that open to crystalline white blossoms with tints of red. The other three are Red Jewel (‘Jewelcole’), Sugar Tyme (‘Sutyzam’), and Golden Raindrops (M. transitoria ‘Schmidtcutleaf’). Crabapples should be planted in full sun where they will easily endure the drought conditions found in the Northwest.
While most perennials need moisture throughout the growing season, some are tougher than a Marine drill sergeant, flowering profusely in spring, then soldiering on with little or no water during the summer. Bear’s breeches (Acanthus caroli-alexandri) produce dramatic, pagoda-like inflorescences, up to three feet tall, that are composed of tiers of hooded flowers. Much more delicate, yet striking as it spreads across the garden floor and flowers, is wood anemone (Anemone nemorosa); flowers range from white to blue or pale pink, and may be single or double.
Hardy geraniums have gained more recognition in recent times as reliable and beautiful perennials. Geranium macrorrhizum will tolerate some drought during the summer, even in a sunny situation; the mats of evergreen foliage are topped with profuse clusters of mid- to light pink flowers in late spring. A number of cultivars have been selected for specific flower color: ‘Album’ (slightly blushed, white flowers with pink stamens); ‘Bevan’s Variety’ (crimson purple); ‘Czakor’ (magenta); and ‘Ingwersen’s Variety’ (soft pink). Use this geranium for springtime color, as an edging for borders, as a contrast with the fine foliage and texture of ornamental grasses, or among sun-loving and drought tolerant woody shrubs.
Other perennials that have been selected for attractive spring blossoms and drought tolerance include: harebell (Campanula rotundifolia), rusty foxglove (Digitalis ferruginea), storksbill (Erodium chrysanthum), as well as certain cultivars of barrenwort (Epimedium), spurge (Euphorbia), Iris, Russian sage (Perovskia), and numerous other geraniums.
Summer brings warm sunny days (maybe even a hot day or two, if we’re lucky!) and what better way to spend a lazy summer afternoon than relaxing in the shade of a leafy tree—perhaps reading the latest issue of Pacific Horticulture. To provide those shady boughs, gardeners have many great options from the GPP roster. Willow oak (Quercus phellos) is a large elegant shade tree, with unusual, narrow, deep green leaves and a strong stately branching habit. In maturity, a well-branched specimen is an excellent climbing tree, and the strong wood is supportive of an average-sized tree house. The fast-growing Heritage river birch (Betula nigra ‘Cully’) is a fantastic accent tree for the garden, notable for its attractive, peeling, multi-colored bark that ranges from cream to salmon to orange red to cinnamon brown. European hornbeam (Carpinus betulus) is a resilient tree with a graceful habit, dark green serrated leaves, and smooth silver gray bark on a trunk that opens into a wide, rounded, lowbranching crown.
For summer foliage color, two cultivars of ninebark have been added to the GPP list for 2011, alongside Diabolo (Physocarpus opulifolius ‘Monlo’, a 2003 selection). The maple-like leaves of P. opulifolius ‘Center Glow’ are a rose burgundy rather than the darker shade of DIABOLO; when the leaves are young, the centers are suffused with yellow and green, resulting in a luminous effect. The new growth of Coppertina (P. opulifolius ‘Mindia’) emerges a molten mixture of orange, red, and copper, then matures to red burgundy. All three of these cultivars grow well in full sun and withstand the annual dry period from July into September.
Among the debutantes of autumn are the groundcover sedums. Early fall is the peak of bloom for these sun and drought-adapted GPP selections. Their clusters of tiny star-shaped flowers are dressed up in shades of yellow, pink, purple red, or raspberry. For various shades of pink flowers, try Sedum spurium ‘Pink Jewel’, S. ‘Bertram Anderson’, or S. pluricaule var. ezawe. Those with yellow flowers include S. kamtschaticum, S. kimnachii, and S. selskianum. An excellent place to view these, and a myriad of other sedums, is Closed Loop Park, north of Lacey, Washington, where the GPP committee conducted an evaluation of Sedum species and cultivars in 2005.
Shrubs laden with berries can also be attractive features of the fall garden. Pyracantha ‘Mohave’, a 2011 GPP, is the first firethorn to be added to the list, selected for its resistance to fire blight and scab, as well as for its abundance of brilliant orange red autumn fruit. Cotoneaster adpressus ‘Little Gem’, C. dammeri, C. procumbens ‘Queen of Carpets’, and C. salicifolius ‘Repens’ make up a sturdy group of non-invasive cotoneasters that are low-growing and spreading—great for rock gardens or cascading over banks and retaining walls—with bright red fruit throughout the fall. Two underused native shrubs, dwarf Oregon grape (Mahonia nervosa) and evergreen huckleberry (Vaccinium ovatum), are often found in the shade of Douglas-firs, but they perform equally well in full sun, plus they sport waxy blue and black purple berries, respectively; as a bonus, the huckleberries are the most delectable of any native shrub.
The Great Plant Picks selection committee of horticulturists continues to add plants with outstanding attributes for the maritime Pacific Northwest. For 2011, there are more than sixty newcomers to the list, many of which will do well under conditions of sun and drought, as discussed here. For a complete list of more than 275 superior plants for garden sites that are sunny and dry, as well as the full list of all the unbeatable GPP selections, please visit www.greatplantpicks.org.
Great Plant Picks for Sun and Drought-tolerance
*new for 2011
Abies pinsapo (5-11, 14-24)
Calocedrus decurrens (2-12, 14-24)
*Chamaecyparis nootkatensis ‘Van den Akker’ (2-6, 15-17)
Crocus tomassinianus (1-24)
Cryptomeria japonica ‘Black Dragon’ (4-9, 14-24)
Helleborus xsternii (4-9, 14-24)
*Ilex crenata ‘Northern Beauty’ (3-9, 14-24)
Juniperus chinensis ‘Kaizuka’ (1-24)
Lonicera nitida ‘Baggesen’s Gold’ (4-9, 14-24)
golden box-leaf honeysuckle
Mahonia xmedia ‘Winter Sun’ (6-9, 14-24)
Microbiota decussata (1-10, 14-17)
Siberian cypress, Russian juniper
Muscari latifolium (1-24)
Narcissus ‘Jack Snipe’ (1-24)
Picea omorika (2b-7, 14-17)
*Pinus flexilis ‘Vanderwolf’s Pyramid’ (1-11, 14-21)
Prunus laurocerasus ‘Mount Vernon’ (4-9, 14-24)
dwarf English laurel
Ribes sanguineum (4-9, 14-24)
Taxus baccata ‘Standishii’ (3-9, 14-24)
columnar golden yew
Trachycarpus fortunei (4-24)
Tsuga mertensiana (1-7, 14-17)
Abelia ‘Edward Goucher’ (5-24)
Allium hollandicum ‘Purple Sensation’
Anemone nemorosa (1-9, 14-24)
Arbutus unedo ‘Compacta’ (4-24)
compact strawberry tree
Berberis 5 ottawensis ‘Royal Cloak’
purple-leaf Japanese barberry
*Camassia cusickii (1-9, 14-17)
Epimedium pinnatum subsp. colchicum ‘Black Sea’ (2-9, 14-17)
Euphorbia characias ssp. wulfenii ‘John Tomlinson’ (4-24)
Geranium macrorrhizum ‘Bevan’s Variety’ (1-24)
Iris pallida ‘Argentea Variegata’ (1-24)
Malus ‘Adirondack’ (1-11, 14-21)
Nandina domestica ‘Gulf Stream’ (4-24)
compact heavenly bamboo
Osmanthus delavayi (4-9, 14-24)
Perovskia ‘Filigran’ (2-24)
cutleaf Russian sage
Pyrus salicifolia ‘Pendula’ (2-9, 14-21)
weeping willow-leafed pear
Sambucus nigra Black Beauty (‘Gerda’) (2-7, 14-17)
purple-leaf black elder
*Tulipa sylvestris (1-24)
*Viburnum carlesii ‘Aurora’ (2-11, 14-24)
Korean spice viburnum
*Artemisia versicolor ‘Sea Foam’ (1-24)
Betula nigra Heritage (‘Cully’) (1-24)
Campsis xtagliabuana ‘Madame Galen’ (3b-24)
hybrid trumpet creeper
Carpinus betulus ‘Fastigiata’ (2-9, 14-17)
Caryopteris incana Sunshine Blue (‘Jason’) (2b-9, 14-24)
red tussock grass
Cornus sericea ‘Hedgerows Gold’ (1-2, 14-21)
variegated red-twig dogwood
Eryngium amethystinum (1-24)
blue sea holly
Eucomis comosa ‘Sparkling Burgundy’ (4-9, 14-24)
Hedera colchica ‘Dentata Variegata’ (3b-24)
Panicum virgatum ‘Shenandoah’ (1-11, 14-23)
*Penstemon ‘Razzle Dazzle’ (6-9, 14-24)
*Phlomis tuberosa (1-24)
tuberous Jerusalem sage
*Physocarpus opulifolius ‘Center Glow’ (1-10, 14-17)
Quercus phellos (2-4, 6-16, 18-21)
Robinia pseudoacacia ‘Frisia’ (1-24)
Salix purpurea ‘Nana’ (1-11)
dwarf purple osier
Yucca flaccida ‘Golden Sword’ (1-9, 14-24)
Acer circinatum (2b-6, 14-17)
Acer Pacific Sunset (‘Warrenred’)
Colchicum autumnale (2-10, 14-24)
Cotinus obovatus (2-24)
Cotoneaster salicifolius ‘Repens’ (3b-24)
Crataegus xlavalleei (3-12, 14-21)
Elaeagnus xebbingei ‘Gilt Edge’ (4-24)
variegated hybrid elaeagnus
Ginkgo biloba ‘Autumn Gold’ (1-10, 12, 14-24)
Mahonia nervosa (2b-10, 14-24)
dwarf Oregon grape
Nyssa sylvatica (2-10, 14-21)
Osmanthus heterophyllus ‘Purpureus’ (4-10, 14-24)
purple-leaf false holly
Parrotia persica (2b-7, 14-17)
Pseudolarix amabilis (2-7, 14-17)
Pyracantha ‘Mohave’ (4-24)
Sedum kamtschaticum (1-11, 14-21)
*Sedum spurium ‘White Carpet’ (1-10, 14-24)
Vaccinium ovatum (4-7, 14-17, 22-24)
Zelkova serrata ‘Village Green’ (3-21)
Great Plant Picks
All selections in the Great Plant Picks have been chosen for their suitability in USDA hardiness zones 7 and 8, which covers most of the Pacific Northwest, west of the Cascades. In the list above, zone numbers in parentheses refer to Sunset zones (when available) in the latest Sunset Western Garden Book, and have been provided as an aid for readers beyond the Northwest. Plants may not perform equally well in all of the Sunset zones noted.
To learn more about the 2011 Great Plant Picks and the nearly 800 plants picked to date, please visit the website at www.greatplantpicks.org.