Gadenin日本語Get the appWilt: sudden, total, and only on some stems
Clematis wilt is a fungal infection that blocks the water-carrying tissue inside a stem. The effect is dramatic and fast. A stem in full leaf and often in bud goes limp from the tip downward over a day, sometimes overnight, and by the second or third day the leaves have blackened and the whole stem is dead. The stems next to it can be completely untouched, which is the clearest sign that this is not a watering problem.
Look low down on the affected stem, at or just above soil level, and you will usually find a discolored, slightly sunken patch where the tissue has darkened. That is where the fungus entered, typically through a wound: a stem crushed by a tie, snapped while training, or damaged by a hoe.
The large-flowered kinds are the ones this happens to. The vigorous small-flowered species types are rarely affected. If your plant flowers in early spring or has masses of small flowers, sudden collapse is far more likely to be a snapped or severed stem than wilt, so check the stem's whole length before assuming disease.
| Symptom | Likely cause | What to do |
|---|---|---|
| One stem limp top to bottom in 1-2 days, others fine | Clematis wilt | Cut the stem out below the damaged point, to below soil level if needed |
| Whole plant droops in afternoon, recovers by morning | Heat stress | Deep soak, mulch, shade the root zone |
| Whole plant limp at dawn, soil dry | Drought | Two gallons (9 l) slowly; repeat in three days |
| Lower leaves yellow, no new growth, soil always wet | Overwatering or poor drainage | Stop watering; improve drainage or lift a potted plant |
| Stem snapped cleanly at a node | Mechanical damage | Cut back to a live pair of buds; tie the rest in more loosely |
| Shoots vanish overnight at ground level | Slugs or snails on new growth | Protect the emerging shoots in early spring; check after dark |
What to do when a stem collapses
Act the same day. Cut the affected stem out completely, following it down past the discolored patch to clean, healthy tissue. If the discoloration goes all the way to the ground, cut below soil level. This is exactly why the crown was planted three to four inches (8 to 10 cm) deep: there are dormant buds below the surface, the fungus has not reached them, and the plant regrows from there.
Do not compost the removed material and do not leave it lying at the base of the plant. Bag it or burn it. Clean your pruners afterwards before using them on anything else.
Then wait. A plant that has lost a stem to wilt often pushes new shoots from below ground within a few weeks in the growing season, or the following spring if it happened late. Keep the soil evenly damp and do not dig around the crown while you are waiting. Plants written off in midsummer regularly reappear the next spring, so give a crown a full season before replacing it.
- Confirm it is wilt, not drought Check whether neighboring stems on the same plant are healthy. Drought and heat affect the whole plant at once; wilt takes individual stems while the rest stay turgid.
- Trace the stem down to clean tissue Run your fingers down the stem looking for a darkened, shrunken section. Cut two to four inches (5 to 10 cm) below it into firm green or pale wood. If in doubt, cut lower.
- Cut below ground if the damage reaches soil level Scrape the mulch and soil back, cut the stem off below the surface, and replace the soil. Buried buds on a deeply planted crown are what regrows the plant.
- Remove and destroy the cut material Take every piece away, including fallen leaves under the plant. Disinfect the blades. Fungal spores overwinter on debris left in place.
- Water, mulch and leave it alone Keep the root zone evenly moist and shaded. Do not feed heavily to force a response and do not fork around the crown. Give it a full season before deciding the plant is gone.
The best defense against wilt is prevention at planting: a deep crown, unhurried handling of stems, and ties that are loose enough not to crush. Most infections trace back to a physical wound, and most wounds happen while tying in growth in a hurry.
Mildew, slugs and the small nuisances
Powdery mildew shows as a white dusty film on leaves and flower buds, usually in late summer on plants that are dry at the root or crowded against a wall with no air movement. It disfigures rather than kills. Improve air flow by thinning congested growth, keep the roots properly watered, and remove the worst affected leaves. Plants that are watered deeply rarely get it badly.
Slugs and snails are the real threat in early spring, when a Group 3 plant is pushing its entire year's growth up from ground level as soft green shoots. A handful of shoots eaten off at the base in one night can set the plant back a month. Check at night with a torch, clear hiding places from around the crown, and protect the shoots until they are a foot (30 cm) tall and toughening.
Earwigs chew ragged holes in petals and aphids cluster on soft growing tips and cause distorted young leaves. Neither is serious on an established plant. Dislodge aphids with a jet of water and accept some petal damage. Reaching for a spray usually costs you more in lost predators than the pests were costing in damage.
Keep a note of what happened and where
Record the date any stem collapses, which plant it was on, and where on the stem the damage started. Wilt tends to recur on the same plants in the same conditions, and two or three entries over a couple of seasons tell you whether a particular position is too hot and dry at the root or whether one plant is simply susceptible.
Also note the date you first see slug damage each spring and the date mildew first appears. Both are strongly tied to the weather in the preceding fortnight, and knowing your own garden's usual timing lets you protect the shoots or improve watering a week before the damage rather than a week after.