Purple clematis has long been a staple in Minnesota gardens. But lately, when gardeners here want a flashy plant, they've tended to gravitate toward exotics like mandevilla or annuals like cardinal vine.
Clematis has a reputation for being finicky and hard to establish, requiring lots of sun, and with a color palette limited to purple. But it's time for Minnesota gardeners to change those perceptions, according to Kathy Donahue Nass, part of the family that runs Donahue's Clematis in Faribault, Minn. Clematis is increasingly diverse and well suited to the Upper Midwest, she said.
"It's a plant that needs a winter to do well, and there are a lot of new plants out there," Nass said. Breeders here and around the world — Donahue's is one of the top three clematis growers and breeders in North America, shipping 850,000 plants per year — are producing clematis varieties that are shorter, fragrant, that thrive in shade, have double flowers and that rebloom or flower for much of the summer. There are brawny old varieties with leaves as big as your hand that need to be trained up a strong trellis and delicate, climbing types with tiny bell-shaped flowers.
But what about growing them? The key to developing strong plants, Nass said, is proper planting.
The old garden saw says clematis likes its head in the sun and feet in the shade, and for many types that's true. Mulching around the base of the plant will help keep the soil cool, but so will surrounding the base with plants like hosta or daylilies or spreading annuals.
Gardeners should dig a hole 18 inches deep to loosen the soil, then plant clematis deeper than they are in the pot, covering up one or two lowest sets of leaves. That helps establish roots and makes the plants produce shoots from below ground, so that even if rabbits chew a plant down or the wind breaks the vine, the plants will bounce back.
"That gets the plant started in the right way," Nass said. "It matters what happens that first year. It's best to prune the plants back to force that underground development. You have to be patient; it pays off later."
Clematis takes about six weeks to get established in the garden. During that time, Nass suggests watering well twice a week. After that, water once a week if it's dry. When an established plant is actively growing, she advises fertilizing once a month with something like Miracle-Gro or applying a time-release fertilizer like Osmocote.
Nass, who has many clematis in her own yard, likes to plant at least two varieties together to mix colors and to stagger bloom. She lets them climb shrubs like lilacs, arborvitae and even a crabapple tree, and she's had people ask why the tree was reblooming in August and September. The fall blooms were from a white sweet autumn clematis that had climbed the tree.
It's safe to plant most clematis as companions with shrubs, Nass said. They're not strong enough to strangle a climbing rose or lilac, though she advises against trying that with heavy, vigorous varieties like Mrs. Robert Brydon, a plant with thick stems and small blue flowers that could overwhelm a small shrub.
One of her easy-to-grow favorites is Viticella Venosa Violacea, which has purple flowers with white centers and does well in sun or part shade. It starts blooming in early July and will flower until frost, she said. Huldine, a white clematis that begins blooming in June, may continue to flower until Labor Day.
Varieties that will tolerate shade include pink Abilene; pink-and-white Nelly Moser, and Silver Moon, a large-flowered mauve variety with extended bloom. The long-flowering Fleuri, with intense purple petals marked by a magenta stripe, grows about 4 feet high and does well in containers.
Betty Corning is an old variety that is short and has fragrant, nodding lilac flowers.
Many newer types, including the double-flowered blue Diamantina, compact Diana's Delight and the shorter red-flowered Rebecca, have been bred to rebloom. Deep purple Sapphire Indigo is very easy to grow, tops out at 4 or 5 feet and can be allowed to sprawl as a groundcover.
Though it can be hard to successfully overwinter potted perennials in Minnesota, short clematis varieties can be grown in containers year after year, according to Nass, provided the pots are at least 18 to 20 inches across, and the gardener has access to an unheated garage. After a hard freeze, cut the plant back to a third of its height and leave it in the garage without water. In mid-April, put the plant outside and resume watering.
More information on clematis is available at clematisinternational.com/ and at the Donahue website at donahuesclematis.com/. Both have information on pruning clematis. Though the pruning question can seem intimidating, as long as you remember the name of your plant variety you'll be able to easily find out when and how to prune.
That leaves one nagging question: Is clematis pronounced CLEM-uh-tis, or clah-MAH-tis?
CLEM-uh-tis, said Nass. Consider the question settled.
Mary Jane Smetanka is a Minneapolis freelance writer and Hennepin County Master Gardener.