How to cut back perennials

Practical UK gardening advice. This guide draws on the video "How to Cut Back Herbaceous Perennials", a useful UK demonstration of autumn border work showing which plants benefit from an autumn cut and how to do it cleanly without damaging crowns.

1. Know which plants to cut now and which to leave

Plants with soft, floppy foliage that collapses after frost - hostas, geraniums (cranesbill types), astrantias, lupins - can generally be cut back in autumn once the foliage has died back properly. These do not offer much in the way of winter interest once they have collapsed.

On the other hand, grasses, sedums, rudbeckias, eryngiums, and other plants with structural seedheads look good through winter and provide food and shelter for birds and insects. Leave these until late February or March. Similarly, slightly tender plants like penstemons and salvias are better left alone - the old stems help protect the crown from frost.

2. Wait for frost to do the first work

There is little point cutting back perennials while they still have green in them. Once autumn frosts have blackened the foliage and the plant has clearly died back, that is when to move in. For most UK gardens that means from mid-October onwards, though in a mild autumn it may be later.

Cutting too early removes foliage that the plant is still using to draw energy back into the roots. It also means you miss weeks of seedhead interest in the border.

3. Cut hollow-stemmed plants low

For plants like delphiniums, hollyhocks, and large rudbeckias that you are cutting back - cut the stems close to the ground, leaving just 5 to 10 centimetres of stub. Hollow stems that sit above the soil can collect water and rot, which can travel down to the crown.

Use sharp secateurs or loppers. A clean cut heals better than a torn or crushed one. If you are cutting through thick clumps, a small pruning saw or strong-bladed loppers are easier than straining secateurs.

4. Hardy geraniums and astrantias: cut right back

Hardy cranesbill geraniums and astrantias can be cut back to ground level once they have finished - they will reshoot from the crown in spring and often produce a fresh flush of growth. Some gardeners do this twice a year, in midsummer and autumn, and get two flushes of flowers as a result.

Do not confuse hardy geraniums (cranesbills) with tender pelargoniums, which are quite different plants. Pelargoniums need to come inside for winter rather than being cut back and left outdoors.

5. Leave structural seedheads for winter interest

Ornamental grasses, rudbeckias, echinaceas, eryngiums, and achilleas all look good in a frost. The seedheads catch low winter light well and birds will visit them for seeds. Leave these until late winter - the garden looks more considered with something to look at through the bare months, rather than just cut stumps.

That said, if a plant has a disease problem - powdery mildew on phlox, for instance - it is better to clear the material away and not leave it to spread spores through winter.

6. Tidy up and compost as you go

Collect cut material in a barrow as you go along the border. Most healthy perennial foliage composts fine in a regular heap - it breaks down faster than woody material. Anything that looks diseased is better in the council green bin than added to your compost.

Once the border is cleared, it is a good time to apply a mulch of garden compost or bark - the soil is still warm and accessible, and the mulch will help over winter. See our guide on mulching garden borders for the how-to on that.

When to call a handyman

Cutting back a large established border is a proper half-day's work. If the garden has been neglected for a season or two and there is more to tackle, Richard can help with border clearance, cutting back overgrown perennials, and general autumn tidy-up jobs across Sandwich and East Kent.