Clematis container gardening means growing a flowering clematis vine in a large, deep pot with a support to climb, its roots kept cool and shaded while the top reaches for sun. Clematis takes well to pot life and brings vertical colour to a patio or balcony with no open ground. The keys are a big enough container, a cool root zone, a trellis or obelisk for support, and steady water and feeding through the season.
Clematis was the plant that finally gave my small paved yard some height. There was nowhere to plant a climber in the ground, so I stood a large pot against the fence, pushed an obelisk into it, and set a purple Jackmanii clematis to climb. Within two summers it covered the obelisk in flower from midsummer on, a sheet of purple at eye level where before there had been a bare fence. The vine asked only for water, feeding, and a hard cut each winter.
Why clematis grows well in pots
Clematis adapts to a container more readily than most climbers. It has a fibrous root system that copes with confinement, and it does not need the deep, far-ranging roots of a tree. Given a big enough pot, it climbs and flowers as well in a container as it does in open ground, which makes it ideal for a patio, balcony, or rented yard with no soil to plant in.
The vine brings something to a small space that few container plants can, which is height and vertical colour. Most pots fill the lower few feet of a patio. A clematis on an obelisk or against a trellised wall draws the eye upward and covers a vertical surface in bloom, using space that would otherwise sit empty. It turns a flat collection of pots into a layered, three-dimensional planting.
There is a wide choice of clematis to suit any spot and season. Early types flower in spring, large-flowered hybrids bloom through summer, and late types carry flowers into autumn. By choosing a mix you can have clematis in flower for months, all grown in pots.
The old rule: feet in the shade, head in the sun
The classic advice for clematis is to keep its feet in the shade and its head in the sun, and it holds just as true in a pot. The vine flowers best when its top growth reaches up into full or part sun, but it resents hot roots. A clematis with its roots baking in a sun-blasted pot grows stressed and flowers poorly, however much sun the top gets. Research from the Royal Horticultural Society has shown that root-zone temperatures above about 80 degrees F / 27 degrees C reduce flower bud set, which is why the feet-in-the-shade rule is not just folklore (RHS advice).
In open ground, gardeners shade the roots with low plants or a slab over the root zone. In a pot, you achieve the same in a few ways. Site the container where the pot itself sits in shade while the vine climbs into the sun, perhaps behind a lower pot or against the shaded base of a sunny wall. Mulch the surface of the pot with stones, gravel, or pebbles to keep the soil cool.
You can also plant something low and leafy around the base of the clematis in the same pot, a trailing annual or a low perennial, to shade the soil and the roots beneath. The clematis climbs up through and over its companion, which guards the cool root zone the vine depends on.
Choosing a pot and planting
Use a large, deep container, at least 18 inches / 46 cm across and just as deep. The depth matters as much as the width, since a deep pot holds a cooler, more even root zone and gives the substantial roots room to spread. A bigger pot also dries out more slowly, which eases the constant summer watering a climber in full leaf demands.
Plant a single clematis per pot in a rich, loam-based potting mix with good drainage. Set the plant deeper than it sat in its nursery pot, burying the lower 2 to 3 inches / 5 to 8 cm of stem. This deep planting protects against clematis wilt (Ascochyta clematidina), the fungal disease that can collapse the top growth suddenly in summer, since if the top dies, the buried buds below soil can resprout. Firm it in and water well.
Set the support in place at planting time. A freestanding obelisk or trellis panel pushed firmly into the pot gives the vine something to climb from day one. Alternatively, stand the pot against a wall or fence fitted with wires or a trellis. Clematis climbs by twisting its leaf stalks around thin supports, so it needs slim canes, wires, or mesh to grip, not a solid post. Anything thicker than about 0.5 inch / 1.3 cm in diameter is too thick for the leaf stalks to wrap.
The first clematis I grew in a pot, I stood proudly in the sunniest, hottest corner of the trial patio, reasoning that more sun meant more flowers. The vine grew, but the flowers were sparse and the leaves looked tired all summer. The problem was the black plastic pot baking in full afternoon sun, which cooked the roots inside. The next spring I slid the plant into a thick glazed pot, mulched the surface with pale gravel, and tucked the container behind a lower pot so the base sat in shade while the vine climbed into the sun. The flowering doubled. The lesson stuck. With clematis, it is the roots that need shade, not the flowers.
Watering and feeding
A clematis in a pot is thirsty, since a full vine of leaf and flower transpires hard and the confined soil dries faster than open ground. Keep the mix evenly moist through the growing season, checking daily in hot weather and watering deeply when the top 1 inch / 2.5 cm feels dry. Let a potted clematis dry out repeatedly and the buds drop and the flowering falters.
The plant is also a hungry feeder that exhausts the nutrients in its pot. Feed every couple of weeks through spring and summer with a balanced liquid feed, switching to one higher in potassium as the flower buds form to encourage a strong display. Top-dress the pot with fresh compost each spring, scraping off the old surface soil and replacing it, to renew the feeding zone.
Mulch the surface after planting and again each spring. A mulch of gravel, stones, or compost does double duty, keeping the roots cool and slowing water loss from the soil. On a hot patio, that cool, moist root zone is what carries the vine through summer in good flower.
Pruning by group
Pruning is where clematis confuses people, but the rule is simple once you know which group your plant belongs to. There are three groups, and each is pruned differently. Get it wrong and you cut off the season’s flowers, so it is worth identifying the type before you reach for the secateurs.
| Group | Flowering time | Where flowers form | Pruning method | Examples |
|---|---|---|---|---|
| Group 1 | Early spring (Apr-May) | Previous year's wood | Tidy after flowering, remove dead or tangled stems | C. montana, C. alpina, C. macropetala |
| Group 2 | Early summer, sometimes reblooming | Old and new wood | Light prune in late winter to a strong pair of buds; tidy again after first flush | 'Niobe', 'The President', 'Henryi', 'Bees' Jubilee' |
| Group 3 | Midsummer to autumn | Current year's growth | Cut all stems to 12 in / 30 cm above soil in late winter | 'Jackmanii', 'Arabella', 'Etoile Violette', 'Princess Diana' |
If you do not know your clematis group and it flowers late in summer, treating it as group three is the safest bet, since you cannot kill the plant with a hard cut and you will at least get flowers on the new growth. If it flowers before June and never again, treat it as group one and just tidy it.
Recommended cultivars for a pot
Most clematis can grow in a pot, but the compact cultivars are far easier to manage. The Royal Horticultural Society has awarded the Award of Garden Merit to a number of container-friendly clematis, including ‘Arabella’ (Group 3, magenta-blue flowers, 4 to 6 feet / 1.2 to 1.8 m), ‘The President’ (Group 2, deep purple, 8 to 10 feet / 2.4 to 3 m), and ‘Niobe’ (Group 2, deep red, 6 to 8 feet / 1.8 to 2.4 m). For smaller pots, the Boulevard series bred by Raymond Evison stays under 4 feet / 1.2 m and flowers for months.
Overwintering container clematis
The roots of a clematis are hardy in open ground, but in a pot they freeze harder and faster from cold air on every side. A potted clematis behaves as if it is two USDA zones less hardy than the same plant in the soil, so a cultivar rated for zone 5 in the ground is only safe to zone 7 in a pot. In a cold climate, protect the container through the worst of winter. Move the pot to a sheltered spot against a wall, group it with other pots, sink it into a spare patch of ground, or wrap the container in insulation.
Mulch the surface of the pot heavily in autumn with bark or leaves to add a protective layer over the roots. The top growth of late-flowering clematis dies back anyway and is cut off in late winter, so it needs no protection. For the early types that keep their old stems, the buds are hardy and need only the root protection a wrapped pot provides. Come spring, top-dress, feed, and the vine climbs and flowers again.