Only some sedums need dividing, and the ones that do need it every 4 to 5 years rather than every season. This page covers which plants, when, and how.
Part of the Complete Sedum Guide.
Which sedums to divide
Divide: the upright Hylotelephium group. H. telephium ('Autumn Joy', 'Matrona', 'Purple Emperor', 'Autumn Fire'), H. spectabile ('Brilliant', 'Stardust'), and the SunSparkler and Rock 'N Grow series. These form clumps that, after 4 to 5 years, develop a dead woody centre with fresh vigorous growth only around the outer edge. At that point division restores the plant.
Do not divide (in the strict sense): the creeping mat-formers. S. acre, S. album, S. spurium, S. rupestre, S. sexangulare, and the rest. These spread by stem rooting rather than crown expansion and do not develop the dead-centre syndrome. You propagate them by taking stem fragments, not by splitting a crown.
Do not divide: the tender rosette sedums. S. morganianum, S. rubrotinctum, S. nussbaumerianum, S. adolphi. These are propagated by leaf or stem cutting, never by division of the root mass.
When to divide
Two windows work for Hylotelephium:
- Early spring as the first crown buds break ground, typically March or early April in a temperate climate. This is the easier window because you can see where the fresh shoots are and cut around them.
- Early autumn after flowering and before the first hard frost, typically mid-September to mid-October. The plant has time to establish new roots before dormancy.
Avoid summer division. The plant is in active flower or bud, and transplant shock costs you the current season's display.
How to divide
- Water the plant thoroughly the day before. A hydrated clump lifts more cleanly.
- Dig a wide circle around the clump, at least 20 cm beyond the visible crown, and lift the whole root ball.
- Shake or rinse off enough soil to see the crown clearly.
- Identify the dead woody centre and the outer vigorous sections. Each division should include 3 to 5 healthy shoot buds and a fist-sized piece of root.
- Cut cleanly with a sharp spade, a clean knife, or (for smaller crowns) two garden forks back-to-back. A torn cut invites rot; a clean cut heals.
- Discard the dead centre. Replant the outer divisions at the same depth they were growing, water in once, and leave alone.
New divisions do not need feeding. They do benefit from a light top-dressing of grit around the crown to prevent water sitting against the cut surfaces.
Division versus propagation
Division replaces a tired clump; it does not usually increase your stock unless the plant is unusually large. For multiplying Hylotelephium, stem cuttings of non-flowering shoots in May or June are faster and produce more plants per parent. Push the lower half of a 10 cm cutting into gritty compost; roots within a fortnight.
For the creeping sedums, "division" in the traditional sense does not apply. What you do is lift a section of mat, pull it into fragments, press the fragments onto moist substrate, and wait a week. The result is the same.
When divisions fail
The common reasons a divided Hylotelephium fails to re-establish:
- The cut was ragged and the wound rotted in wet soil. Cut clean, replant in well-drained ground.
- The division was too small. A piece with fewer than three shoot buds can work but often sulks for a season.
- The plant was moved in full flower. Transplant before flowering or after.
- The soil was too rich. Feeding a fresh division produces soft growth that flops and invites fungal problems. No feeding.
A successful division looks no different from the parent within one growing season.