How deep should I plant a clematis?

Nearly every plant in a garden goes in at the depth it was growing in the pot. Clematis are the deliberate exception, and the reason is clematis wilt: a fungal disease that collapses whole stems, sometimes overnight, and which is far commoner on the large-flowered hybrids than on anything else. A clematis planted at pot level and struck by wilt has nothing left to shoot from. A clematis planted deep has buds waiting below ground and usually comes back.

What you'll need

• Spade
• Bucket of water for soaking the pot
• Well-rotted organic matter or garden compost
• Bamboo canes
• Soft ties
• Paving slab, stones or low planting to shade the roots (optional)
• Slug protection for the first season (optional)

Step by step

1. Water the plant thoroughly before you start.Stand the pot in a bucket until the bubbles stop. A dry rootball planted into dry soil often never wets up properly at all.
2. Dig the hole out from the wall or fence, not against it.At least 300 to 450mm out. The strip against a wall is permanently dry, in the rain shadow, and is usually the worst soil on the plot. Clematis are thirsty and hungry, and this single decision affects them more than almost anything else.
3. Dig it wider and deeper than the pot.Roughly twice the width, and deep enough to drop the rootball 75 to 100mm below the surrounding soil level. Fork the base and sides so roots can get out.
4. Improve the soil you will backfill with.Mix garden compost or well-rotted manure into the excavated soil. Do not fill the hole with neat compost — it slumps and the roots stay in the pocket.
5. Set the plant so the rootball top is 75 to 100mm below the surface.Lay a cane across the hole to judge it. The stem will be buried for that distance, covering several leaf joints. Those buried joints carry dormant buds, and they are the whole point of the exercise.
6. Angle the plant back towards its support.Lean the rootball and the supporting cane so the stems travel from the planting position to the wires or trellis at a gentle angle. Bending stems sharply at the base snaps them, and clematis stems are brittle.
7. Backfill and firm, then water in generously.Firm in layers with your hands rather than stamping, then water with at least a full can, slowly, so the soil settles round the roots.
8. Keep the stems intact — do not cut down to the buried section.The buried stem stays there permanently. Group three clematis are cut back to 200 to 300mm above ground each winter, which is well above the buried part, and even that leaves the underground buds untouched.
9. Shade the root run.A paving slab, a group of stones, a low shrub or a mulch over the root area keeps the soil cool. The traditional formula — head in the sun, feet in the shade — is a genuine cultural requirement, not a piece of folklore.
10. Protect the new shoots from slugs in the first spring.Emerging clematis shoots are a favourite target, and a young plant can be eaten to the ground before it gets going. This is the commonest cause of a first-year clematis that simply disappears.
11. Water deeply through the first two summers.A thorough soak once or twice a week in dry weather rather than a daily sprinkle. Clematis are among the thirstiest wall plants there are.

Tips

• Prune a newly planted clematis hard in its first spring — down to about 300mm — whatever its group. It feels wasteful and it produces a plant with several stems from the base instead of one bare stalk.
• The deep planting rule matters most for the large-flowered hybrids, which are the ones that get wilt. Montana, alpina, macropetala and the viticella types are far more resistant, but planting them deep does no harm.
• Buy a plant with more than one stem coming from the compost if you can. Single-stemmed clematis are one slug or one wilt attack from nothing.
• Do not plant a clematis in the dry hole left by digging a shrub out of a wall bed without replacing and improving the soil first.

Common mistakes

• Planting at the same level as the pot — It removes the plant's only insurance against clematis wilt. If the top collapses there are no buried buds to regrow from and the plant is lost.
• Planting tight against the wall — Permanent drought at the roots, which shows as poor growth, few flowers and mildew, and is nearly always misread as a disease problem.
• Leaving the root area bare and sunbaked — Clematis roots want to stay cool and moist. Bare soil against a south-facing wall in July is neither.
• Skipping the first-year hard prune — You get one long stem with all the growth at the top and a permanently bare base. Cutting back in the first spring produces multiple stems from low down.

If it doesn't work

Questions people ask