Great Plant Picks: Ninety-one for 2008

By: Richie Steffen

Richie Steffen is curator of horticulture for the Elisabeth C Miller Botanical Garden in Seattle, where he manages the rare…

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All photographs courtesy Great Plant Picks: Alan Dodson (AD) David Mason, Hedgerows Nursery (DM) J Frank Schmidt & Son Co. (FS) Richie Steffen (RS) Lynne Thompson (LT)

All photographs courtesy Great Plant Picks: Alan Dodson (AD) David Mason, Hedgerows Nursery (DM) J Frank Schmidt & Son Co. (FS) Richie Steffen (RS) Lynne Thompson (LT)

Since the launch of the Great Plant Picks program eight years ago, almost 500 plants have been selected as the most reliable garden-worthy plants that can be grown in the maritime Pacific Northwest. This unique awards program brings together more than thirty horticultural professionals from nurseries, botanical gardens, and the landscape industry to identify the best choices for gardens from Eugene, Oregon, to Vancouver, British Columbia, and from the Cascade Mountains to the Pacific Coast. This year, ninety-one plants have been added to the comprehensive list of Great Plant Picks. These picks represent several collections of related plants, and others resulting from plant evaluations held throughout the region in the last few years.

Flowers of American fringe tree Chionanthus virginicus (FS)

Flowers of American fringe tree Chionanthus virginicus (FS)

Small Trees for Small Gardens

Many of this year’s picks are excellent options for the urban landscape. Despite their size, smaller gardens can hold an array of interesting yet easy-to-care for ornamentals. Trees must be chosen carefully, considering scale, branching structure, and seasonal interest, to get the most from these pinnacles of the garden. Golden full moon maple (Acer shirasawanum ‘Aureum’) is a stunning example of a tree useful as a focal point. Slow growing, a twenty-year old tree will only reach twelve to fifteen feet tall and about as wide. The new spring foliage emerges a vibrant lemon yellow that will tone down to rich chartreuse later in summer.

Chinese fringe tree (Chionanthus retusus) is a slightly larger choice, maturing at around twenty feet tall. Flaky bark provides year-round interest; lacy, fringe-like, flowers appear in midsummer. The more shrub-like American fringe tree (C. virginicus) can easily be trained into a multi-stemmed tree. Lowbranching, with a similar lacy white bloom, it will grow to about fifteen feet tall with an equal spread in ten to fifteen years. Both fringe trees are dioecious, male and female flowers being formed on separate plants. Male trees produce copious displays of the fringed flowers; female trees are more subtle in their floral beauty, but will produce showy clusters of blue black fruit into the late summer. A lone female fringe tree will still produce fruit even without a male for pollination, but will have a heavier set with a partner nearby.

Golden full-moon maple Acer shirasawanum ‘Aureum’ (LT)

Golden full-moon maple Acer shirasawanum ‘Aureum’ (LT)

For late summer flowers, try seven son flower (Heptacodium miconioides), a large shrub that can easily be pruned into a small tree fifteen to eighteen feet tall with a slightly narrower spread. Small, fragrant white flowers are borne in clusters at the branch tips in August and early September. After the blossoms drop, the calyx gradually turns red and remains showy until obscured by red and yellow fall foliage.

Sugar maples (Acer saccharum), known for spectacular autumn color, are not often thought of as trees for a small garden. Indeed, most of GPP’s sugar maple selections will ultimately become too large for many urban spaces, but two of them are well suited for this purpose. Acer saccharum Apollo (‘Barret Cole’) and ‘Temple’s Upright’ (also known as ‘Monumentale’) are columnar types that can serve in many useful landscape roles. Apollo sugar maple is unique because it is not only columnar but also dwarf; mature trees will reach about twenty five feet tall and spread about ten feet wide. ‘Temple’s Upright’ has a strong central leader almost twice the height of Apollo and ultimately will have a slender oval profile.

Japanese forest grass Hakonechloa macra (RS)

Japanese forest grass Hakonechloa macra (RS)

Plants for Dry Shade

Drought tolerance is much the catch phrase of gardening these days; finding plants that thrive in dry and shady locations can be especially difficult. Cornus sericea ‘Baileyi’ and ‘Hedgerows Gold’ are selections of our native red-twig dogwood that will tolerate a moderate degree of both drought and shade. The rich yellow variegation of ‘Hedgerows Gold’ makes it stand out in the garden. This was discovered by nurseryman David Mason and has been generously shared with many. Two native ground covers that are top performers in dry shade are oak fern (Gymnocarpium dryopteris; western forms are now classified as G. disjuncta) and redwood sorrel (Oxalis oregana). Oak ferns will form a delicate carpet with fresh, bright green, fine-textured fronds. The new fronds emerge in early spring and start to die down in early autumn. Underplant this fern with Cyclamen hederifolium to add fall and winter interest until the fern returns next spring. There are several selections of redwood sorrel, including some that are evergreen in the Northwest; all will form a thick blanket preventing weeds from encroaching. In spring, the mat is dotted with pale pink to rose flowers.

Colorful calyxes of seven son flower Heptacodium miconioides (RS)

Colorful calyxes of seven son flower Heptacodium miconioides (RS)

A stalwart shrub for the shade garden is aucuba (Aucuba japonica). These resilient evergreen shrubs can be the backbone of almost any shade garden. Aucuba japonica ‘Goldstrike’ illuminates the dark woodland with leaves dusted with golden-yellow spots. For something a little more sedate, try A. japonica ‘Serratifolia’. Its dark evergreen leaves will add depth to background plantings. Wintergreen barberry (Berberis julianae) will also work well in the back of the shade garden. It has the added bonus of becoming a formidable hedge, with stems covered in sharp spines. A word to the wise: avoid planting beneath deciduous trees, so that fallen leaves will not have to be picked out of its prickly branches.

Wood fern Dryopteris lepidopoda (RS)

Wood fern Dryopteris lepidopoda (RS)

The Herbaceous Layer

Perennials and bulbs can really pull a garden together by adding color and texture to make a good landscape great. To add interest and extend the blooming season, try the fall-blooming Amaryllis belladonna, seductively called naked ladies. In late August or early September, the dormant bulbs send forth two-foot-tall, spear-like stalks that burst into rich pink trumpet flowers heralding the coming of fall.

Soon after naked ladies end their sultry show, Colchicum enters the scene. Erroneously given the common name of autumn crocus, due to the flower’s superficial goblet-like resemblance to true crocus blossoms, these robust bulbs erupt from the bare ground with stemless flowers in September and October. Two selections with distinct features to recommend them are C. autumnale and C. ‘Waterlily’. Colchicum autumnale offers profuse, cup-shaped, lilac-pink flowers about six inches tall; C. ‘Waterlily’ has fully double flowers truly reminiscent of real water lilies (Nymphaea).

Variegated Japanese forest grass Hakonechloa macra ‘Albostriata’ (RS)

Variegated Japanese forest grass Hakonechloa macra ‘Albostriata’ (RS)

I always look to foliage for textural elements that will establish a sense of continuity in the garden. Japanese forest grass (Hakonechloa macra) is dynamic for linking the landscape together; even the typical green form, is anything but plain. The thin, ribbon-like leaf blades stand twenty-four to thirty inches tall, forming gently arching mounds that may approach eight feet wide at maturity. The variegated form ‘Albostriata’ is about one-third smaller and slower growing. The light variegation of this selection adds color to the garden without shouting “look at me—I’m gold and green!” I find its more refined mounding habit suggests flowing water when the breeze blows through. Sometimes, subtlety is not the way to go: to give a little punch of color, plant a few clumps of H. macra ‘All Gold’. Mounds of brilliant, acid yellow leaves slowly mature to about twelve to eighteen inches tall and three to four feet wide. With a half-day of morning sun, it will keep this intense coloring until fall; with a little more shade, it will tone down to clear chartreuse. This bright smaller grass looks great with the bold fronds of thick-stemmed wood fern (Dryopteris crassirhizoma) or the orange bronze new growth of sunset fern (Dryopteris lepidopoda); both of these ferns are new additions to the GPP list.

Autumn crocus Colchicum autumnale (LT)

Autumn crocus Colchicum autumnale (LT)

As we push the Great Plant Pick list toward the 600-plant mark, we hope you will find many wonderful choices for your garden and see many plants that may already be doing well there. Be sure to check out the website, where you can read more about the plants noted above, as well as all the other choices from this and past years.

Fruit of American fringe tree Chionanthus virginicus (AD)

Fruit of American fringe tree Chionanthus virginicus (AD)

2008 Great Plant Picks

Perennials and Bulbs
Amaryllis belladonna (4-24)
naked ladies
Arisarum proboscideum
   mouse plant
Begonia grandis subsp. evansiana (3-24)
hardy begonia
Calamagrostis acutiflora ‘Karl Foerster’ (2b-24)
Campanula lactiflora and cultivars ‘Loddon Anna’ and ‘Prichard’s Variety’ (1-9, 14-24)
milky bellflower
Cardamine trifolia
   three-leaf cardamine
Ceratostigma willmottianum (4-9, 14-24)
Miss Willmott’s plumbago
Chaerophyllum hirsutum ‘Roseum’
hairy chervil
Colchicum ‘Waterlily’ (2-10, 14-24)
double-flowered autumn crocus
Colchicum autumnale (2-10, 14-24)
autumn crocus
Cynara cardunculus (4-9, 12-24)
cardoon
Darmera peltata and ‘Nana’ (2-7, 14-20)
umbrella plant and dwarf umbrella plant
Digitalis ferruginea (1-10, 14-24)
rusty foxglove
Digitalis grandiflora (1-10, 14-24)
large yellow foxglove
Disporopsis pernyi
   evergreen Solomon’s seal
Dryopteris crassirhizoma
   thick-stemmed wood fern
Dryopteris cycadina
   shaggy shield fern
Dryopteris lepidopoda
   wood fern
Eryngium agavifolium
   agave-leafed sea holly
Eryngium alpinum (2-24)
alpine sea holly
Gymnocarpium dryopteris (syn. Dryopteris disjunctum)
common oak fern
Hakonechloa macra (2b-9, 14-24)
Japanese forest grass
Hakonechloa macra ‘Albostriata’ (2b-9, 14-24)
variegated Japanese forest grass
Hakonechloa macra ‘All Gold’ (2b-9, 14-24)
golden Japanese forest grass
Leucojum aestivum ‘Gravetye Giant’ (1-10, 14-24)
summer snowflake
Leucojum vernum (1-6)
spring snowflake
Muscari latifolium (1-24)
grape hyacinth
Oxalis oregana (evergreen form) (4-9, 14-24)
evergreen redwood sorrel
A collection of candelabra primulas:
   Primula beesiana (3-6, 15-17)
   P. bulleyana (3-6, 15-17)
   P. japonica and cultivars ‘Miller’s Crimson’ and ‘Postford White’ (2-6, 15-17)
   P. poissonii
Rodgersia aesculifolia
(2-9, 14-17)
finger-leaf rodgersia
A collection of Sedum spurium cultivars (1-10, 14-24):
‘Doctor John Creech’, ‘Fuldaglut’, ‘Pink Jewel’, ‘Purpurteppich’, ‘Raspberry Red’, ‘Ruby Mantle’, ‘Schorbuser Blut’ (syn. ‘Dragon’ Blood’), and ‘Tricolor’

Tulipa clusiana (1-24)

lady tulip
Woodsia polystichoides
   holly-fern woodsia

Golden Japanese forest grass Hakonechloa macra ‘All Gold’ (RS)

Golden Japanese forest grass Hakonechloa macra ‘All Gold’ (RS)

Shrubs and Vines
Aucuba japonica ‘Goldstrike’ (4-24)
variegated Japanese aucuba
Aucuba japonica ‘Serratifolia’ (4-24)
Japanese aucuba
Berberis buxifolia ‘Nana’ (4-9, 14-24)
dwarf Magellan barberry
Berberis julianae (4-24)
wintergreen barberry
Berberis verruculosa (4-9, 14-24)
warty barberry
Camellia sasanqua ‘Yuletide’ (4-9, 12, 14-24)
Campsis tagliabuana ‘Madame Galen’ (3b-24)
hybrid trumpet creeper
A collection of Clematis montana cultivars (3b-9, 14-18):
‘Broughton Star’, ‘Elizabeth’, ‘Freda’, ‘Pink Perfection’ and ‘Tetrarose’
Cornus sericea ‘Baileyi’ (1-9, 14-21)
red-osier dogwood
Cornus sericea ‘Hedgerows Gold’ (1-9, 14-21)
golden-twig dogwood
Cotoneaster adpressus ‘Little Gem’ (2-24)
creeping cotoneaster
Cotoneaster dammeri (2-24)
bearberry cotoneaster
Enkianthus perulatus (3-9, 14-21)
white enkianthus
Grevillea victoriae (8, 9, 14-24)
royal grevillea
Heptacodium miconioides (2b-6, 14-17)
seven son flower
Hydrangea aspera ‘Villosa Group’ (4-9, 14-24)
fuzzy hydrangea
A collection of Hydrangea macrophylla cultivars (3b-9, 14-24):
‘Amethyst’, ‘Ayesha’, ‘Glowing Embers’, ‘Merritt’s Beauty’, ‘Merritt’s Supreme’ and ‘Nikko Blue’
Kalmia latifolia ‘Elf’ and ‘Sarah’ (2-7, 16, 17)
mountain laurel
Lonicera pileata (3b-9, 14-24)
box-leaf honeysuckle
Spiraea japonica Magic Carpet (‘Walbuma’) (2-10, 14-21)
Japanese spirea

Acer saccharum APOLLO ‘Barret Cole’ in autumn (FS)

Acer saccharum APOLLO ‘Barret Cole’ in autumn (FS)

Trees and Conifers
A collection of Acer saccharum (sugar maple) cultivars (1-10, 14-20):
‘Barret Cole’ (Apollo), ‘Commemoration’, ‘Green Mountain’, ‘Legacy’ and ‘Temple’s Upright’
Acer shirasawanum ‘Aureum’ (3b-9, 14-16)
golden full moon maple
Aesculus parviflora
   bottlebrush buckeye
Betula nigra and Heritage (‘Cully’) (1-24)
river birch
Carpinus caroliniana (1-9, 14-17)
American hornbeam
Carpinus japonica
   Japanese hornbeam
Chamaecyparis obtusa ‘Spiralis’ and ‘Split Rock’ (2b-6, 15-17)
dwarf Hinoki cypress
Chionanthus retusus (3-9, 14-24)
Chinese fringe tree
Chionanthus virginicus (2-6, 15-24)
American fringe tree
Fargesia robusta
   fountain bamboo
Juniperus chinensis ‘Kaizuka’ (1-24)
Hollywood juniper

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.

Golden-twig dogwood Cornus sericea ‘Hedgerows Gold’ (DM)

Golden-twig dogwood Cornus sericea ‘Hedgerows Gold’ (DM)

Great Plant Picks: An Educational Program of the Elisabeth Carey Miller Botanical Garden

Great Plant Picks is one of the Miller Garden’s educational outreach programs. Under its auspices (and funded by the Pendleton and Elisabeth Miller Charitable Foundation), expert horticulturists from Oregon, Washington, and British Columbia (west of the Cascade and BC’s Coast ranges) meet throughout the year to make their annual selections.

Visit the Great Plant Picks website (www.greatplantpicks.org) to learn more about the nearly 600 plants picked to date, with images and fact sheets that include culture and companion plants for each of the winners.