If you’d like to enjoy the spectacular blooms of Clematis, you need to understand two key points. First, Clematis needs lots of sun but wants cool, rich, moist soil to grow in. Second, Clematis vines want to climb, and are happiest when they can run as high as possible during their growing season.
The best location for most Clematis is against a high fence or wall in full sun, with the roots in shade. Some large-flowered hybrids fade badly if they get too much sun and these should be planted in where they’ll get morning sun only or partial shade. Clematis roots should be in cool, moist, rich soil, without competition from shrub or tree roots. A good way to do this is to plant the Clematis against a wall, behind foundation shrubs. Roots should be well protected from damage or disturbance; stay away from them if you’re digging or cultivating.
Old-fashioned chicken wire makes the best support for Clematis vines, since they can’t grasp thick branches or heavy trellising. Most trellises Are too short, too smooth, and with their slats too far apart or Clematis. If you use a decorative trellis, attach chicken wire to the back. This is easy to do with “zip-ties” or wire., and won’t show at all once the vines cover it. Established Clematis vines can easily climb ten to fifteen feet each season, so give them as tall a structure as you possibly can. Allow a few inches of ventilation space behind your trellis.
Clematis plants are often sold “bare root” or in tiny pots. It’s well worth it to get larger plants with a big root system; these will perform much better much sooner. Clematis has a very large root system, so pretend you’re planting a tree. Dig a planting hole as large as possible (two feet deep and wide is ideal), throw away the excavated soil, and replace it with topsoil. Mix plenty of composted manure and peat moss with the planting soil, plus some Plant Tone or similar perennial fertilizer. Plant with the base of the plant one to two inches below the soil surface.
Use groundcover plants, shrubs, mulch (or some combination), to keep the sun off the root zone; shallow-rooted perennials like pachysandra, creeping phlox, hardy geranium, candytuft, or vinca vines cool the soil without competing. In dry seasons, water deeply once a week.
Early-flowering Clematis and large-flowered hybrids bloom in spring, from buds produced the previous season. Prune these back as soon as possible after bloom but don’t cut into the woody trunks. Prune again in February or March by removing dead and weak stems, then cut back remaining stems to the topmost pair of large, plump green buds.
Late-flowering Clematis bloom on the last two to three feet of the current season’s growth. Some types begin blooming in mid-June and continue into the fall. This is the easiest group to prune since no old wood needs to be maintained. In February or March cut each stem to a height of about two to three feet, including some good stems and buds. Eventually the length of the bare stem at the base will increase as the vine matures.
Fall-blooming Clematis is a different plant entirely. Also called Sweet Autumn Clematis, this is a fast-growing hardy vine covered with small white blooms with an intense sweet smell. It’s great for covering chain-link fences with a downy blanket. It is such an aggressive climber it can be a bit of a nuisance, and it can also self-seed, but in the right spot it’s a terrific performer and a traditional garden classic.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.