How to Divide Perennials

Dividing perennials is one of the easiest ways to get more plants for free. It also keeps established clumps healthy and flowering well.

Why divide perennials?

• Free plants: One large clump can become three, five or more new plants.
• Rejuvenation: Old clumps often die out in the centre. Dividing removes the dead parts and gives the healthy sections room to grow.
• Better flowering: Congested plants flower less. Division encourages vigorous new growth.
• Control size: Some perennials spread aggressively. Division keeps them in check.

When to divide

The general rule is to divide spring and summer flowering plants in autumn, and autumn flowering plants in spring. This gives them time to establish before they need to flower.

• Autumn (September-October): Divide hostas, geraniums, astilbe, hemerocallis (daylilies), primulas.
• Spring (March-April): Divide asters, sedums, grasses, rudbeckia, echinacea.

Avoid dividing in summer when plants are stressed by heat, or in winter when the ground is frozen.

How to divide

1. Water the plant well the day before dividing.
2. Cut back any tall top growth to make handling easier.
3. Dig around the clump with a spade, lifting the whole root ball.
4. Shake or wash off excess soil so you can see the roots.
5. Pull or cut the clump into sections, each with roots and shoots.
6. Discard the old, woody centre if it has died out.
7. Replant the divisions immediately at the same depth as before.
8. Water well and keep moist until established.

Different techniques for different plants

• Fibrous roots (hostas, hemerocallis): Pull apart by hand or cut with a sharp knife.
• Tough clumps (grasses, agapanthus): Use two forks back-to-back to lever apart, or cut with a spade.
• Fleshy roots (iris): Cut rhizomes with a knife, keeping a fan of leaves on each piece.

Aftercare

• Water regularly until the divisions are established.
• Mulch around the plants to retain moisture.
• Do not feed immediately – wait until you see new growth.
• Protect from slugs, which love tender new shoots.

Plants that should not be divided

Some perennials resent disturbance and are better left alone or propagated by other methods:

• Peonies (divide only if essential, and expect no flowers for a year or two)
• Hellebores (can be divided but recover slowly)
• Plants with taproots like lupins and oriental poppies