Lift the plant with a fork, taking enough soil to avoid damaging the roots. Shake off as much soil as possible, washing it off if necessary. Tease the roots apart and cut out large well-rooted crowns for replanting. Plant the small pieces also, - you will probably be lucky !
What do I do with Polyanthus after flowering?
Various forms of primrose and polyanthus can be split and replanted as soon as they finish flowering. Set the new divisions in ground refreshed with bonemeal and compost. Each rosette of leaves can be prised away from the mother clump, with roots attached.
Do Polyanthus come back every year?
The name Polyanthus describes hybrids of P. vulgaris (Primrose) and P. veris (Cowslip) and these plants are often treated as bedding and discarded each year. Fact is, they are perennial and will come back the following year especially if planted in favourable conditions.