Dividing Perennials

I’m clearing a few areas in the garden this week that have become overgrown. Doing this has unearthed a few perennials that have gone bald in the centre. Plants like this slowly expand along the ground leaving the old bit in the middle to die off. This is very common in lower growing perennial plants such as creeping asters. My perennial geraniums are also taking over a whole bed so are being divided too although I’m not really sure where to put them as yet.

Most perennials benefit from division every two to three years to maintain health and vigour. For the purposes of propagation, this can be done more regularly to build up stock.

These are just a few examples of plants that can be divided:, Anemone, arum lily, aster, bergenia, buttercup, daylily, delphinium, euphorbia , hosta, Iris, lily-of-the-valley , ornamental grasses, primula (primrose), sedum, verbena and sea holly,

When to divide perennials

Plants can be divided successfully at almost any time if they are kept well-watered afterwards. However, division is most successful when the plants are not in active growth.

As a general guideline, divide summer-flowering plants in spring (Mar-May) or autumn (Sep-Nov) when the soil is dry enough to work. In wet autumns, delay until spring. Spring is also better suited to plants that are a touch tender

Many spring-flowering plants, such as irises, are best divided in summer (Jun-Aug) after flowering when they produce new roots. I find that I generally divide the plants when I have the time.

Dividing perennials

Lift plants gently with a garden fork, working outwards from the crown’s centre to limit root damage. Shake off excess soil so that roots are clearly visible

Some plants, such as Ajuga (bugle), produce individual plantlets which can simply be teased out and replanted. In the case of chamomiles, these grow plantlets form the existing leaves and can be snipped off and replanted without disturbing the parent plant.

Small, fibrous-rooted plants such as Heuchera, Hosta and Epimedium can be lifted and pulled apart gently. This should produce small clumps for replanting

Large, fibrous-rooted perennials, such as Hemerocallis (daylily) require two garden forks inserted into the crown back-to-back. Use these as levers to loosen and break the root mass into two sections. Further division can then take place. You might find hostas need treating this way if they get really huge. In some cases, a sharp knife might be needed to cleave the clump in two

Plants with woody crowns (e.g. Helleborus) or fleshy roots (e.g. Delphinium) require cutting with a spade or knife. Aim to produce clumps containing three to five healthy shoots.

Dividing rhizomes.

Dig up and select young outer pieces.

Use a sharp knife to separate the rhizomes.

Select pieces that have at least one or two fans of leaves from the outside of the clump and discard the centre rhizomes.

Plants with rhizome roots include: Flag Iris, Lily of the valley and Orris Root.

Aftercare

Plant divisions as soon as possible and water them in well. Alternatively, pot up individually to build up size, overwintering pots in a frost-free environment.

Problems

There are few specific problems associated with dividing, especially if carried out between autumn and spring. However, ensure that plants don’t dry out while they do re-establish. It is also worth carrying out slug and snails control as these are often problematic pests for perennials.

Why Divide?

There are a few good reasons to divide your perennial plants:

• Clumps have started to die out in the middle. The classic “doughnut” shape with an empty hole in the centre is a sure sign that a perennial clump needs attention.
• Flowering performance has declined. The clump may have become congested, or the roots old and woody.
• Soil nutrients have been exhausted around the clump. Signs of this might be stunted growth, yellowish leaves or lack of bloom. Dividing and moving to a new location is a wise idea. Sometimes simply fertilizing the plant will make it smarten up.
• Perennial weeds like creeping buttercup or grass have infested the clumps. When this happens, usually the best approach is to dig up the entire clump and divide it, picking out every single piece of weed root that can be found.
• Dividing established clumps can provide plenty of new plants for a new garden bed, or to share with friends and neighbours.

There are a few perennials that don’t respond well to being divided which include: Alyssums candytuft, carnation, delphinium, foxgloves, lavenders and the perennial sweet pea amongst others.

Once you start to divide plants, you will get a feel for those that will do well when divided.