How to divide rosette petrocosmea

Rosette Petrocosmea multiplies by producing offsets — small plantlets around the base of the parent. Dividing is simply a matter of separating those once they are big enough, which is far less disruptive than splitting a whole clump. Wait until an offset is roughly a third the size of the parent and has visible roots of its own before detaching it.

Early spring as growth restarts is the safest window; after flowering also works for many plants.

Ease the whole plant out of its pot, brush the compost away from the base, and separate the offset where it joins the parent — most come away with gentle pressure. If it does not, cut it free with a clean sharp knife, keeping as many of its own roots as possible.

Pot each division into fresh compost at the same depth it was growing before, water it in well, and keep it somewhere bright but out of direct sun for two to three weeks while new roots take hold. Do not feed straight away — damaged roots take up fertiliser poorly and it can scorch them.