Gadenin日本語Get the appWhy the group decides everything
Nearly every case of a healthy clematis that will not flower comes down to the same mistake: the plant was cut at the wrong time for its group. Group 1 carries next year's flowers on the stems it grew this year, so a tidy-up in late winter removes every flower bud on the plant. Group 3 flowers only on growth made in the current season, so leaving it uncut produces a tangle of dead-looking old stems with a few flowers stranded at the very top.
The plant is not sulking and it is not underfed. It is doing exactly what its group dictates. Get the group right and clematis pruning becomes one of the simplest jobs in the garden, because each group needs one decision made once a year.
You do not need a label to work this out. The flowering time gives you the answer, and it is the same answer every year, so one season of watching settles it permanently.
| Group | When it flowers | Flowers on | Pruning |
|---|---|---|---|
| Group 1 | Early to mid spring | Stems grown last season | Only after flowering, and only to control size |
| Group 2 | Late spring to early summer, often a second flush in late summer | Old wood for the first flush, new growth for the second | Light tidy in late winter; take out dead and weak stems only |
| Group 3 | Midsummer through autumn | Growth made this season | Hard cut to 12 in (30 cm) in late winter, every year |
Identify the group from a single season of watching
Leave the plant unpruned for one year and watch it. If the first flowers open in early spring, before the plant has made much new growth, and they open along stems that were already there over winter, it is Group 1. These are usually the vigorous, small-flowered, mass-flowering kinds that cover a fence in one wave and then stop.
If the first flowers open in late spring or early summer, are large, and appear on short side shoots coming off woody stems that overwintered, it is Group 2. Many of these produce a second, usually smaller flush on the current season's growth in late summer, which is the giveaway.
If nothing happens until midsummer and the flowers appear on soft green growth that started at ground level or low down that same year, it is Group 3. These plants often look completely dead in late winter, which is exactly what they should look like, because everything above ground is going to be cut off anyway.
One further clue: if the whole plant dies back to the ground of its own accord over winter, it is Group 3 with certainty. Group 1 and Group 2 keep a permanent woody framework.
- Note the week the first flower opens Not the month. The week, relative to your own last frost, is what you need. Early spring, late spring to early summer, or midsummer onward maps directly onto Groups 1, 2 and 3.
- Look at what the flower is attached to Follow the flower stalk back. If it comes off brown, woody, overwintered stem, the plant flowers on old wood, which means Group 1 or Group 2. If it comes off green growth that ran up from the base this year, it is Group 3.
- Watch for a second flush A large-flowered plant that flowers in early summer, pauses, then flowers again in late summer on the new tips is Group 2. That second flush is the clearest single indicator there is.
- Write the group on a permanent label Scratch it into a metal or plastic tag, or record it against the plant's position in your notes. Nursery labels fade within two seasons and that is when the wrong cut gets made.
How to cut each group
Group 1: prune only if you need to control the size, and only in the weeks immediately after flowering finishes. Cut back the stems that have flowered, taking out whole lengths rather than trimming every tip, and leave the plant the rest of the season to grow the wood that will flower next spring. Cutting a Group 1 in winter removes the entire coming display. Many Group 1 plants need no pruning at all for years.
Group 2: in late winter, before growth begins, work over the plant stem by stem. Remove anything dead, broken or spindly, and shorten the remaining stems back to the highest pair of fat, healthy buds. Fat buds are visibly plumper than the flat, dead-looking ones further up. Do not shear the top off; the flower buds you want are on the wood you are about to remove if you cut carelessly. If a Group 2 has become bare at the base, cutting one or two of the oldest stems right down to twelve inches (30 cm) each year rebuilds it over three seasons at the cost of some flowers.
Group 3: in late winter, cut every stem to about twelve inches (30 cm) above the ground, just above a strong pair of buds. That is the whole job. It feels brutal and it is correct. The plant will produce six to ten feet (2 to 3 m) of new growth and flower on it from midsummer. Skipping this cut for even one year leaves you with flowers only at the top of a bare tangle.
If you genuinely do not know the group and cannot wait a season, treat the plant as Group 2 and prune lightly in late winter, removing only dead stems. You will not get the best from a Group 3 that year, but you will not destroy a Group 1's display either. Light pruning is the safe default when in doubt.
Cuts that cause problems
Cut just above a pair of buds, not in the middle of a long internode. The stub above the buds dies back, and on the large-flowered kinds that dieback is one of the routes clematis wilt uses to get into the plant. Leave no more than half an inch (1 cm) of stem above the buds.
Use clean, sharp pruners, and clean them again if you have just cut out a stem that collapsed suddenly with wilt. Crushed, ragged cuts heal slowly and the wound stays open to infection for longer.
Never pull dead stems out of a tangle by hand. Clematis stems snap at the node with almost no force, and a stem you break at ground level in late winter is one you will not see flower in the season ahead. Cut the stem into short lengths and lift them out piece by piece instead.