Gadenin日本語Get the appDivide only when there is a reason
A peony does not need dividing to stay healthy. Left alone in a good position, a clump flowers better each decade and can outlive the gardener. Division is a setback, not maintenance. Every plant lifted loses most of its fine feeding roots and spends the following two to three years rebuilding them, with few or no flowers in the meantime, and there is no technique that avoids this.
So divide only for a real reason: you want more plants, the clump has to move because of building work or a bed being redesigned, the crown has been buried too deep and is no longer flowering, or the center has genuinely deteriorated after very many years. Wanting to tidy the border is not a reason.
Do not divide a young plant. Wait until a clump has been in place at least four or five years and is flowering strongly. Dividing a three year old plant that has only just started to perform sets it back to the beginning, and neither the parent nor the divisions are worth having for several seasons.
The commonest use of division is a rescue, not an increase. A peony that makes lush leaves and no flowers is nearly always planted too deep, and the only cure is to lift it in early autumn and reset the crown with the eyes 1 to 2 in (2.5 to 5 cm) under the surface.
Early autumn, and only early autumn
Lift and divide in early autumn, once the foliage has begun to tire but while the soil is still warm. At that point next year's eyes are fully formed and clearly visible on the crown, so you can see what you are cutting, and there are still several weeks of warm soil for new roots to grow into before winter.
Spring division is a mistake. In spring the plant has already committed its stored reserves to shoots that are pushing upward, the eyes are fragile and easily knocked off, and the divisions face a whole summer with a damaged root system and no root growth season to recover in. A spring divided peony commonly loses three years rather than two, and a proportion simply die.
Work on a cool, overcast day and keep the lifted root out of the sun and wind. Exposed peony roots dehydrate quickly and a shriveled division establishes badly. If you cannot replant immediately, wrap the root in damp sacking or bury it temporarily in moist soil in the shade, and get it planted within a day or two.
Lifting, cutting and replanting
Dig a wide trench right round the clock of the clump, starting at least 12 in (30 cm) out from the outermost stems, and work down and under. Peony storage roots are brittle and go deep, so expect to break some; that is acceptable. Lever the whole clump out rather than pulling it up by the stems, then wash or gently hose the soil off so you can see the crown and count the eyes.
Aim for divisions with three to five eyes and a good length of storage root attached. Three to five is the sweet spot: fewer eyes and the division takes an extra year or two to reach flowering size, more and the piece is really an undivided clump that will not settle any faster than the original. Use a clean, sharp knife and cut deliberately through the crown between eyes rather than tearing the plant apart.
Discard anything soft, hollow, dark inside or foul smelling, and cut back damaged root ends to clean tissue. Then replant immediately at the correct depth, with the topmost eye 1 to 2 in (2.5 to 5 cm) below the finished surface. It is remarkably easy to do everything else right and then bury the new divisions too deep, which converts a two year setback into a permanent failure to flower.
| Division type | Eyes per piece | Expected first real flowering |
|---|---|---|
| Single eye piece with one root | 1 | Third or fourth spring, sparse at first |
| Small division | 2 | Third spring |
| Standard division | 3 to 5 | Second or third spring |
| Large piece, barely divided | 6 or more | Second spring, but no faster to settle |
| Whole clump lifted and reset for depth | All | Second or third spring after resetting |
Seed, and what to write down
Peonies can be raised from seed, but it is a long project rather than a way of getting plants. Fresh seed sown in autumn and left outdoors typically needs two winters before it germinates, and the seedlings then take four to seven years to reach flowering size. Seedlings do not resemble the parent plant, since garden peonies are hybrids, so seed raising is for the curious and for breeders rather than for replacing a plant you like.
After dividing, record the date, the number of divisions, the eye count of each and where each one went in the garden. Those notes are the only thing that will tell you, two springs later, whether a flowerless young plant is simply a one eye division running to schedule or a division that was accidentally planted too deep.
Also note the measured depth of each new division, exactly as you would for a newly bought root, and mark the positions physically in the bed. Peonies emerge very late and freshly planted divisions are invisible for months. An unmarked division is the one that gets dug through when you plant something else in early spring.