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Shimmering aspen gold and blazing canopies of Maple-when we think of autumn, most of us conjure up images of foliage. As daylight hours shorten and hints of frost fill the air, the annual spectacle of changing leaves transforms our landscapes with dramatic bursts of color. Not to be overlooked are numerous late-blooming perennials, with rich and vibrant color displays enlivening the garden scene-golden yellows of black-eyed Susan, goldenrod and coreopsis, the deep roses of sedums like Autumn Joy and Purple Coneflower, or the violet blues of salvias, asters and Russian sage.
Chrysanthemums deliver a palette of harvest colors: wines, rusts, salmons, yellows, violets, whites and rosy pinks. The ever-popular florist's mums (C. moriflorium) are found in stores and garden centers all around town this time of year. But before you're tempted by their charm, remember that many of these showy mums are the hothouse-grown "cushion" variety. They are certainly attractive, and great for containers or seasonal decoration, but they may not your best option for the perennial garden. Chances are they won't return next year.
Taller and hardier perennial performers, such as C. rubellum (bright pink 'Clara Curtis' is a favorite), should be selected from locally grown or "hardened-off" stock offered by local nurseries and garden centers. Spring is a better time for selecting and planting all these dependable varieties of perennials, as they will have plenty of time to develop healthy root systems needed to survive winter.
Other outstanding late-season performers and their suggestions for their use in the garden are listed. Plant these with companion plants to compliment or contrast foliage and flowers. Plants within each group share similar cultural requirements, like soil, water and sunlight. While they are outstanding in the fall, some provide interest nearly all year round.
Ornamental Grass Combination: Helictotrichon sempervirens (blue oat grass, Blue Avena Grass). Gracefully arched sprays of thin, blue-green spears allow it to stand alone as a specimen, be used in mixed plantings or combined with other grasses. Pair with Schizachyrium scoparium (little bluestem), which turns deep shades of red, orange and purple with cool fall nights. Blue oat displays tawny, feathered seed heads from mid-summer through winter. Little bluestem grass flowers in late summer to early fall. Contrast the linear form of blue oat grass with the ferny green foliage and dainty yellow blooms of Coreopsis 'Moonbeam'. Add some rose-red floral notes with low-growing sedums, such as 'Rosy Glow', 'Emperor's Way', or smoky-leaved 'Vera Jameson'.
Water-Wise Attractions: Agastache rupestris (sunset hyssop) is a 1997 Plant Select and a treasure for the low-water fragrance garden. Its neon flower spikes (shifting between salmon and violet) and sweet scent (licorice or root beer) attract hummingbirds, butterflies and bees. From mid-summer through fall, the flowers wave atop three foot tall stems laced with thin, silver-green leaves. Left standing through winter, seed heads provide food for birds and textural interest. Equally fragrant and water-thrifty companions include silver and blue Russian sage and lavender varieties 'Munstead', 'Hidcote' or 'Grosso'. A front border plant to add a touch of yellow in spring with tiny button flowers is Santolina chamaecyparissus (lavender cotton). All prefer full sun and well-drained soil. Leave foliage through winter and prune back in late spring to newly emerging growth.
A Shrub for All Seasons: Viburnum trilobum (American cranberrybush viburnum) blooms in spring with white "lace cap" flowers, and in late summer edible red berries appear with its maple-like leaves turning a stunning wine-red. It can be used as a hedge plant, or as a specimen in back of a mixed border. Combine with Heliopsis (False Sunflower) 'Lorraine Sunshine', whose variegated cream and green leaves provide attractive contrast to the viburnum's solid green summer foliage. Golden yellow, daisy-like flowers last until first freeze. Eupatorium purpureum (Joe Pye weed), which grows on sturdy stalks, five to six feet tall, is a back-border companion. With deep olive-green foliage and large, dark rose flower heads that mature in late summer, it makes an excellent plant for both fresh and dried floral arrangements, or let it remain standing for winter interest. In the front of the border, plant Ceratostigma plumbaginoides (Plumbago). The shiny dark green leaves turn reddish-purple in fall and its flowers, arriving in late summer and lasting through light frost, are deep electric blue. These plants perform best in moderately moist soils but will tolerate some dryness. The above plants are somewhat shade-tolerant.
Heaven-Scent: Sweet Autumn clematis (Clematis terniflora) is not a well-behaved vine like most of its earlier-blooming relatives. It will climb to the top of your roof and cover an entire wall if you let it, but it's not a bad option with perfumed clouds of starry-white blooms produced in late summer. After blooming, enjoy its silvery seed fluffs. Give it a sturdy fence or trellis to climb on or let it form a lush canopy over an arched entryway. An option is to plant it as a backdrop for the magenta flames of burning bush (Euonymus alata). For another red, white and green combo, choose a burgundy-leaved barberry (Berberis ssp.). Prune your fall-blooming clematis hard in spring after danger of frost is past.
For more information on perennials, see Colorado State University Fact Sheet #7.405 "Herbaceous Perennials" and #7.231 "Xeriscaping: Garden Flowers." These, and many others, can be found by visiting ext.colostate.edu.
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