Few sights are as dispiriting as a clematis in full bud that collapses within a day or two. The usual verdict is "clematis wilt", but this fungal disease is only one of several reasons a clematis droops, and the right response depends on the cause.
What clematis wilt is
True wilt is caused by the fungus Calophoma clematidina, formerly Phoma or Ascochyta clematidina. The RHS says it survives in the soil on dead plant material, and its spores are splashed onto leaves and young stems. Paul Margot, writing on Clematis on the Web, adds that spores spread by rain splash rather than wind, need moist conditions and often arrive on nursery plants that show no symptoms.
Symptoms to look for
Shoots wilt suddenly, often just before flowering; leaves develop spots and shrivel, and leaf stalks turn black. Split a stem lengthwise and you may find a blackened lesion, often around 10cm long, at or just below soil level. The roots are often not killed, so healthy new shoots may appear from the base.
Timing is a clue: true wilt typically strikes in late spring and early summer, while stems are soft and buds are swelling, and it often follows a wet spell.
Which clematis are at risk
Large-flowered hybrids are the main victims. The RHS names 'Henryi', 'Vyvyan Pennell', 'Mrs N. Thompson', 'Duchess of Edinburgh', 'William Kennett', 'Marie Boisselot' and 'Ernest Markham' as particularly susceptible, with 'Comtesse de Bouchaud', 'Jackmanii' and 'Nelly Moser' also susceptible.
If you have lost plants to wilt before, these are a sensible next choice; our guide to combining clematis with roses suggests several viticellas.
Is it really wilt?
The RHS stresses that wilting in resistant species and hybrids is very unlikely to be caused by this fungus. Before you cut anything, try the British Clematis Society's test: soak the plant thoroughly and check after an hour. If the stems still droop, wilt is likely.
Wilt or something else?
| Clematis wilt | Drought | Slugs or damage | |
|---|---|---|---|
| After a one-hour soak | Still drooping | Stems recover | Still drooping |
| Main clue | Black stain inside stem | Dry soil at the roots | Grazed, twisted or snapped stem |
| Most at risk | Large-flowered hybrids | New and wall-side plants | Young stems at the base |
| What to do | Cut to healthy tissue | Water deeply | Protect and tie in |
Root problems can also stop roots working: Phytophthora root rot, honey fungus, waterlogging and, in pots, vine weevil grubs. Stress matters too, since wilt usually strikes plants already short of water in shallow, dry soil or hot, exposed sites.
Other problems that can look similar
Clematis slime flux, caused by bacteria entering damaged tissue, produces a foul-smelling ooze from a dead or dying stem. Powdery mildew leaves a greyish-white coating on the leaves but doesn't cause sudden collapse.
What to do if your clematis has wilt
Treating a plant with wilt
- Cut backRemove wilted stems to healthy tissue that isn't stained black, even to ground level.
- Bin, don't compostDispose of the material promptly so it doesn't contaminate the soil.
- Clear the baseRemove fallen leaves and plant debris from around the plant.
- Clean upDisinfect secateurs; don't move infected plants or soil around the garden.
- Feed and waterSupport regrowth through spring and early summer, for example with a clematis or rose fertiliser.
- Keep watchingCheck regularly and remove any new symptomatic stems promptly.
The RHS states that no chemicals are available to treat clematis wilt, so the response is cultural: hygiene, cutting back and good growing conditions.
Will it recover?
Usually, yes. Plants are not killed outright, and new shoots generally arise from the base, though you may lose that year's flowers. Shoots can take several weeks to appear, so don't dig a plant up in a hurry.
If a susceptible cultivar collapses year after year, dig it out. The British Clematis Society says the soil is not affected and another clematis can go in the same place; Paul Margot advises against another large-flowered hybrid. A resistant species or a viticella satisfies both views.
Why deep planting helps
Large-flowered hybrids are planted deeper than they sat in their pot: 5–7.5cm below soil level according to the RHS, 10–15cm according to the British Clematis Society. Buried stems carry dormant buds, so if wilt kills the top growth the plant can regrow. Paul Margot notes a downside: on old, deeply planted plants, buried lesions may keep the infection going.
Deep planting is about recovery, not immunity. Our guide to planting a clematis gives the depth for each type.
Prevention
Water deeply in dry spells, especially in the first few years (see feeding and watering clematis), then work through the rest of the list.
Prevention checklist
- Buy vigorous plants; check the stem bases
- Resistant types for difficult, exposed sites
- Deep cultivation and organic matter
- Mulch to keep roots cool and moist
- Slug protection for young stems
- Stems tied in so wind can't twist them
Check for drought, slugs and damage first; if a large-flowered hybrid has blackened stems, cut back to healthy tissue (to ground level if needed), dispose of the debris, then feed and water. Plants usually regrow from the base, and resistant species avoid the problem.
Sources
- Clematis wilt (RHS) — Cause (Calophoma clematidina), symptoms, susceptible and resistant cultivars, control without chemicals.
- Clematis wilt (Clematis on the Web, article by Paul Margot) — Rain-splash spread, stem lesions near soil level, recovery from the base and buying healthy plants.
- What's wrong… (British Clematis Society) — The one-hour soak test, stress as a trigger, cutting back and replanting advice.
- Clematis problems: frequently asked questions (RHS) — Other causes of wilting shoots: slugs, root diseases, waterlogging, vine weevil and dry soil.