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How and when to divide garden perennials
Garden Care & How-To
How and when to divide garden perennials
Dividing perennials sounds more dramatic than it usually is. In many cases, it simply means lifting one overcrowded clump, splitting it into a few healthy pieces, and replanting them so they have room to grow again.
Done at the right time, it can refresh tired plants, improve flowering, control size and give you a few extra plants for other parts of the garden. Done at the wrong time, or with the wrong plant, it can become a spade-based regret.
Here’s how to divide garden perennials, when to do it, and which plants are better left alone.
The quick answer
- divide summer- and autumn-flowering perennials in spring
- divide many spring-flowering perennials after flowering or in early autumn
- divide ornamental grasses mainly in spring
- divide peonies only when necessary, usually in autumn
- avoid dividing tap-rooted plants unless you have a very good reason
What does dividing perennials mean?
Dividing is a method used for many clump-forming herbaceous perennials. These are plants that return from the roots or crown each year, often dying back or reducing growth in winter.
Over time, some perennials form large clumps. The centre may become woody, bare or less productive, while the stronger growth moves towards the outside. Division lets you remove the tired sections and replant the healthier pieces.
A good division should have both roots and shoots. You are not trying to chop the plant into tiny scraps. Think “strong new clump”, not “botanical coleslaw”.
Why divide perennials?
- improve flowering
- refresh an old or tired clump
- remove a dead or bare centre
- stop a plant taking over too much space
- create more plants for another border
- reduce flopping caused by overcrowded growth
- keep a border balanced
When is the best time to divide perennials?
For most suitable perennials, the main windows are spring and early autumn.
Spring is usually the easiest time for beginners. The plant is starting back into growth, the weather is generally mild, and the new divisions have the full growing season to settle in.
Early autumn can also work well while the soil is still warm and there is natural rainfall to help plants establish. The key is to avoid leaving it too late. Cold, saturated soil is not a welcoming place for fresh divisions.
In Dublin gardens, heavy soil and winter wet are common enough to take seriously. If your border holds water after rain, spring is often a kinder time to divide than late autumn.
Good perennials for beginners to divide
- hostas
- hardy geraniums
- heucheras
- daylilies
- astilbes
- sedums, now often listed as Hylotelephium
- many clump-forming border perennials
Plant exceptions worth knowing
- Hostas Best timing: Spring or late autumn. A good beginner choice. Large clumps may need a sharp spade or knife.
- Hardy geraniums and heucheras Best timing: Spring or autumn. Often easy to pull apart by hand if the clump is not too dense.
- Daylilies Best timing: Spring or autumn. Fibrous clumps may need two garden forks placed back-to-back to lever them apart.
- Bearded irises Best timing: Summer after flowering. Replant rhizomes near the soil surface. Do not bury them deeply.
- Ornamental grasses Best timing: Mostly spring. Large clumps can be tough. Wear gloves, especially with sharp-edged grasses.
- Crocosmia Best timing: Spring. Divide corm chains carefully and replant at roughly the same depth.
- Dierama Best timing: Spring, only when needed. Dislikes disturbance and may take time to flower well again.
- Peonies Best timing: Autumn, only when necessary. Long-lived and best left alone unless they need moving or have stopped performing.
- Tap-rooted plants such as Baptisia Best timing: Avoid routine division. These are difficult to divide and usually best left undisturbed once established.
When not to divide perennials
- the weather is hot and dry
- the soil is waterlogged
- the plant is in full flower
- the plant is weak, diseased or badly stressed
- the ground is frozen or very cold
- you do not have somewhere suitable to replant the divisions
- the plant is known to dislike disturbance
What you need
- a garden fork
- a sharp spade
- secateurs
- a sharp knife for smaller divisions
- gardening gloves
- a bucket or trug
- compost or soil improver
- a watering can or hose
How to divide perennials step by step
- Water first if the soil is dry If the ground is dry, water the plant the day before. Moist soil is easier to work with and the plant will be under less stress. You want workable soil, not a mud festival.
- Cut back old top growth Remove dead stems or tired foliage so you can see the base of the plant clearly. In spring, you may already have short new shoots showing. In autumn, trim back enough to make the clump easier to handle.
- Lift the whole clump Push a fork or spade into the soil a little away from the crown of the plant. Work around the clump gradually, loosening it from several sides before lifting. Try to keep as much root as possible. Some damage is unavoidable, but gentle lifting gives the new divisions a better start.
- Shake off loose soil Gently shake or tease away some loose soil so you can see the roots and natural divisions. This helps you work out where to split the plant.
- Split the clump How you divide depends on the plant. For soft, loose clumps, pull sections apart gently by hand. For fibrous clumps such as hostas or daylilies, use two garden forks back-to-back and lever them apart. For dense or woody crowns, use a sharp spade or knife to cut cleanly through the clump. Each new section should have healthy roots and several strong shoots or buds. Discard dead, woody or weak material from the centre.
- Replant promptly Replant your divisions as soon as possible. Choose the healthiest pieces and plant them at roughly the same depth they were growing before, unless the plant has special planting-depth requirements. Prepare the soil first by removing weeds and adding compost or soil improver if needed. Do not just shove the division into a tired hole and hope for the best. Plants notice these things.
- Water well Water the divisions thoroughly after planting. This settles soil around the roots and helps the plant start establishing. Keep an eye on them for the next few weeks, especially in dry weather. Newly divided plants do not have a full root system yet, so they need a little patience while they settle.
What to do with spare divisions
Spare divisions can be replanted elsewhere in the garden, shared with another gardener, or potted up temporarily.
If potting them, use suitable compost, water them in, and keep them somewhere sheltered while they recover. Do not leave bare-root divisions sitting around in the sun while you “just do one more job”. That is how plants become crisps.
Aftercare
- keep the soil evenly moist while roots establish
- protect new divisions from drying winds where possible
- mulch around plants to help retain moisture, keeping mulch away from the crown
- remove weak or damaged growth
- avoid heavy feeding immediately after division
A simple timing guide
- Divide in spring hostas, daylilies, many summer- and autumn-flowering perennials, ornamental grasses and crocosmia.
- Divide after flowering or in early autumn many spring-flowering perennials.
- Divide in summer after flowering bearded irises.
- Divide in autumn only when needed peonies.
- Avoid routine division tap-rooted plants such as Baptisia and butterfly weed.
The beginner’s golden rule
If you are not sure, identify the plant before you dig.
Take a photo of the leaves, flowers, whole clump and plant label if you have one. Once you know what the plant is, you can decide whether it should be divided in spring, autumn, after flowering, or not at all.
And sometimes the best advice is to leave it alone. Gardening has enough digging already.
