When to prune your flowers

Are you a garden hygienist?

In my experience, most gardeners fall into two camps when it comes to autumn tidiness: complete clear-out merchants that leave nothing out of place; or the more relaxed, let-it-all-rot-down-naturally brigade. Me? I fall somewhere in the middle. I’ll tidy if there’s a good reason for it, but leave well alone if it’s just offending my natural sense of order. Take the herbaceous border, for example. It’s still full of color from the asters and sedums, rudbeckias and heleniums, but most of the other early flowering plants are past their best and could be cleared away. But take a closer look. See how seemingly dead silhouettes take on a new lease of life in the watery light on early October mornings as the mists start to clear, or when bathed in the honey-glow of a fine autumn evening. Bear in mind they’ll look even more dramatic after a hoar frost in the depths of winter. Watch and listen, too, how the plumes of ornamental grasses and other airy seed heads rustle and move in sussurating synchronicity as they trace the progress of every breeze.

Then consider whether the fallen foliage could be serving another useful purpose. If a perennial is only borderline hardy for your garden, for example, you might be better off leaving the foliage intact to help provide winter protection. Fallen leaves and stems also offer a winter refuge for many types of garden wildlife, while seed heads offer food for the birds and other creatures throughout the winter months. Bear these things in mind too before you consign it all to the compost heap.

Some herbaceous perennial plants will be looking the worse for wear because they have been attacked by a pest or disease, such as powdery mildew or the ever-present slugs and snails…they’re out in force after the wet summer in my borders, but where plants look good in their fading days I leave them to age gracefully. Where this is not the case, clear affected leaves and any pests you come across to help reduce the carry-over of the problem next year.

Dealing with grasses

To make the most of ornamental grasses, you need to tidy them at least once a year. This is a simple task, but one often overlooked. I think it’s partly because they are otherwise such undemanding plants, but also because grasses are looking their best in autumn. They get forgotten until mid-spring when the new growth is showing, making it too fiddly to cut back. Ornamental grasses, such as Festuca and Carex need next to no attention – simply comb through the foliage with your fingers during late winter or early spring to remove dead foliage and seed heads. However, if you want to stimulate new growth and better leaf color, you can cut them back in early spring. Other grasses, such as Deschampsia, Stipa, Pennisetum and Miscanthus should be cut back in late winter, removing last year’s stems and dead leaves before the new foliage appears. Taller varieties of Molinia tend to collapse in late autumn and so are worth tidying before Christmas, though smaller varieties, such as the variegated Molinia caerulea subsp. caerulea ‘Variegata’, often remain upright throughout the winter and can be cut back before the new growth appears in spring. A few grasses can self seed prolifically. In my garden pheasant-tail grass likes to scatter itself around, but I find a thick mulch makes it easy enough to weed out the seedlings in spring. Vigorous grasses can spread rapidly by underground runners and so it’s worth checking at least once a year and severing any runners with a sharp spade to restrict their spread.

My A-Z checklist for choppers

Acaena Trim fading flower heads in late October, but leave the evergreen foliage to provide winter interest.
Acanthus Cut seed heads back in December, but leave evergreen foliage to provide winter protection. Tidy foliage in March.
Achillea Cut down flowering stems to near ground level in November. Tidy foliage in March.
Aconitum Cut down flowering stems to within 15cm of ground level in November. Always wear gloves since all parts of the plant are poisonous and a potential skin irritant.
Acorus If not already done, cut back faded flower stems to near ground level in October.
Actaea Leave flowering stems for winter interest, then remove to near ground level when the berries have fallen or been eaten, usually December. New plants should be cut back in November to prevent wind-rock.
Adiantum Cut back tatty fronds to near ground level in March.
Agapanthus Leave foliage and use as winter wrapping to protect the crown from frost between October and April. In colder areas, insulate the crown with a layer of dry leaves or chipped bark.
Agastache Leave flowering stems for winter interest, then remove to near ground level in March.
Ajuga Trim off damaged leaves in March. Use a sharp spade to cut around the plant and restrict its spread. This will prevent the center of the plant dying out too.
Alcea Remove and burn rust-infected plants, replace with new in the spring. Trim healthy plants to within 15cm of ground level in October to prevent wind-rock in winter.
Alchemilla Prevent self-seeding by removing seed heads as they fade. Cut foliage back to within 3cm of ground level during November.
Alstroemeria Cut back to about 20cm of ground level in October and insulate the crown with a layer of dry leaves or chipped bark.
Amsonia Cut right back to near ground level in November.
Anaphalis Cut foliage right back to near ground level during November and insulate the crown with a layer of dry leaves or chipped bark.
Anchusa Cut back old flowering stems to near ground level during October.
Anemone Remove and burn disease-infected plants. Remove dead flower stems from healthy plants in November, cutting them back to near ground level.
Anthemis Cut back old stems by half during October, but in cold gardens leave foliage to provide winter protection. Then cut back to within 15cm of ground level in March.
Anthericum Cut back stems to near ground level after flowering.
Aquilegia If not already done, cut border species right back to near ground level in October, but take care not to damage the new shoots. Alpine species need deadheading only.
Arabis If not already done, cut back faded flower stems in October. Remove reverted green shoots from variegated varieties.
Armeria Trim off faded flower stems but leave evergreen foliage.
Artemisia Cut herbaceous species to within 3cm of ground level during October. Leave the variety ‘Powis Castle’ until March.
Aruncus Cut back stems to near ground level during October.
Asphodeline Leave flowering stems for winter interest, then remove to near ground level in February.
Asplenium Cut back tatty fronds to ground level in March.
Aster Cut back fading flower stems to about 15cm of ground level during November.
Astilbe Leave flowering stems for winter interest, then remove in February.
Astrantia Cut back faded flower stems to near ground level during November.
Ballota Cut back flower stems in December, but leave foliage to provide winter protection.
Baptisia Cut back faded flower stems to about 15cm of the ground during October.
Bellis Deadhead regularly to prevent self-seeding and remove tatty foliage in March.
Bergenia Cut back faded flower stems to near ground level and remove damaged leaves during November.
Blechnum Cut back tatty fronds to ground level in March.
Brunnera Cut back faded flower stems during October. Remove reverted green shoots from variegated varieties.
Caltha Remove damaged leaves during October and again in March.
Campanula If not already done, cut back flowering stems to near ground level in October. Trim leaves from perennial species in November. Remove and burn rust-infected plants.
Carex Comb through the plant during March to remove dead foliage.
Catananche Trim off faded flower stems to about 15cm during October.
Centaurea Cut back flower stems to near ground level in November, but leave foliage until March.
Centranthus Cut back faded flower stems during October, earlier if self-seeding is a problem. Tidy foliage in March.
Chelone Cut back stems to 15cm during October.
Chrysanthemum Cut back faded flower stems of hardy types to about 15cm during November, but leave foliage until March.
Cimicifuga Cut back flowering stems to near ground level during November. Tidy foliage in March.
Cirsium Trim off faded flower stems to near ground level during October, earlier if self-seeding is a problem. Tidy foliage in February.
Clematis (herbaceous) Cut back all herbaceous species to near ground level in March, except C. recta and C. heracleifolia which should be cut back to a pair of healthy buds about 15cm from the ground.
Codonopsis Cut back stems to about 15cm during November.
Convallaria Cut back stems to near ground level during November.
Convolvulus Trim back herbaceous perennial forms in March to keep within bounds.
Coreopsis Cut back stems to about 15cm during November.
Cortaderia Cut back half way to main clump in February. Wear gloves to protect hands from razor-edged leaves.
Corydalis Cut back stems to near ground level during November, earlier if self-seeding is a problem.
Cosmos After the foliage has died back cut back the stems to within 5cm of the ground in March. Protect the crown with a layer of dry leaves or chipped bark in winter.
Crambe Cut back stems to about 15cm during November.
Crocosmia Cut back flowering stems to near ground level in November, but leave evergreen foliage to provide winter protection – removing it in early March. In cold gardens, lift corms in October.
Cynara Avoid the temptation to remove the faded flowerheads in autumn as they provide interest in the winter garden. Cut them off only when they go brown and soggy. Where temperatures fall below -15°C (5°F) protect the crown of the plant with a layer of dry leaves or chipped bark.
Dahlia Traditional advice dictates that once the first frost has blackened the foliage, cut the main stems back to within 15cm of the ground and label. Then, carefully lift and clean the tubers and allow them to dry naturally indoors. Place the dry tubers in a shallow tray, just covered with slightly moist potting compost, sand or vermiculite. Store in a frost-free place, checking frequently over the winter months. However, if grown on well-drained soils in milder gardens they can be left in situ with the roots protected with a layer of dry leaves or chipped bark in winter.
Delphinium Cut back stems to 30cm of the soil during November and remove dead leaves from around the crown. Cut back stems to near ground level in March.
Deschampsia Cut back foliage in February before new shoots appear.
Dianthus Trim off faded flower stems, but leave evergreen foliage. Large clumps can be cut back to 15-20cm during March to keep compact.
Diascia Trim off faded flower stems to their base during October. Cut back further, if necessary, in March.
Dictamnus Cut back stems to about 15cm during November.
Dicentra If not already done, cut back dead foliage to near ground level in October.
Dierama Cut back flowers to their base in November, but leave foliage until March. In cold gardens, lift corms in October.
Digitalis If not already done, cut back second flush faded flowering stems to near ground level during October.
Doronicum Cut back stems to near ground level during November.
Dryopteris Cut back tatty fronds to near ground level in March.
Echinacea Cut back flowering stems to near ground level during October.
Echinops Cut back flowering stems to near ground level during November.
Epimedium Trim off damaged leaves in February.
Eremurus If not already done, cut down stems after flowering to near ground level in October. Protect the crown with a layer of dry leaves or chipped bark.
Erigeron Cut back stems to near ground level during November.
Eryngium Avoid the temptation to cut back the flowerheads in autumn as they provide interest in the winter garden. Remove them to their base during February.
Erysimum Trim lightly when flowers fade to keep plants compact.
Eupatorium Cut back stems to near ground level after flowering.
Euphorbia If not already done, cut faded flower stems to near ground level in October to encourage bush growth, carefully avoiding new shoots from the crown.
Fargesia Cut back tatty stems to ground level in March and thin others as necessary.
Festuca Comb through the plant to remove dead foliage and trim off seed heads in February, earlier if self-seeding is a problem.
Filipendula Cut back flowering stems to near ground level during October.
Foeniculum If not already done, cut back to 30cm in October and remove flowers to prevent self-seeding. Tidy plants again in March.
Fragaria Remove and burn disease-infected plants. Cut back leaves on healthy ones to within 10cm of ground level in October.
Gaillardia If not already done, trim stems to about 15cm of ground level in October.
Gaura Leave flowering stems for autumn tints, then remove to their base in February.
Gentiana If not already done, remove faded flowers to prevent rotting in October.
Geranium Cut back deciduous varieties after autumn color has finished during November. Semi-evergreen varieties should be deadheaded only.
Geum Trim off faded flowers and damaged leaves in November.
Gladiolus Before the first frost, when the foliage starts to yellow usually October, cut the main stem back to 3cm above the corm and carefully lift and clean the and allow them to dry naturally indoors. Place the dry corms in a shallow tray and store in a cool, frost-free place.
Gunnera Cut right back during November and use leaves to protect the crown or insulate with a layer of dry leaves or chipped bark.
Gypsophylla Cut back flowering stems to near ground level during October.
Hakonechloa Cut back to main clump during March before new shoots emerge.
Helenium Cut back dead stems to near ground level during November.
Helianthus Cut back faded flower stems to near ground level during October.
Helichrysum Cut back stems to near ground level during March.
Helictotrichon Cut back faded flower stems to main clump in March.
Heliopsis Cut back to about 15cm during November.
Helleborus Trim off dead or diseased leaves. Remove seed heads in November and again in March.
Hemerocallis Cut back faded flower stems to near ground level during October.
Hesperis Cut back to about 15cm of ground level during November.
Heuchera Trim off damaged leaves in March.
x Heucherella Shear off faded flower stems in October. Trim off damaged leaves in March.
Hosta Cut back faded flower stems and leaves to near ground level during November.
Iberis Trim off faded flower stems in October, but leave evergreen foliage.
Imperata Cut back during March before new shoots emerge.
Incarvillea Trim off dead foliage during October, protect the crown with a layer of dry leaves or chipped bark.
Inula Cut back to about 15cm of ground level during November.
Iris (large-flowered) If not already done, cut back stems in each fan into an arrow shape, with the tallest stem cut about 15cm from ground level during October. Iris sibirica varieties should be left until March.
Knautia Cut back the faded flower stems down to near ground level in October.
Kniphofia Cut back faded flower spikes to near ground level. Protect borderline hardy varieties by tying leaves together.
Leucanthemum Cut back faded flower stems to near ground level in November.
Lamium Trim off damaged leaves in February.
Lathyrus Cut back everlasting peas to about 30cm from the ground during November. Then cut back to about 15cm of ground level in March.
Liatris Cut back to near ground level during November.
Ligularia Tidy plants during November. Cut back to near ground level during March.
Limonium Cut back to about 15cm during November.
Linaria Cut back to about 15cm from the ground during November.
Linum Cut back faded flower stems to ground level in November.
Liriope Cut back faded flower spikes to near ground level during October.
Lobelia Trim off dead foliage, protect the crown with a layer of dry leaves or chipped bark.
Lupinus If not already done, cut back second flush of faded flowering stems to near ground level during October and remove dead leaves.
Lychnis Cut back to near ground level during November.
Lysichiton Cut back dead foliage in October. Remove self-sown seedlings as part of routine border maintenance in early spring.
Lysimachia Trim back yellow loosestrife to about 15cm of the ground in November, leave Creeping Jenny until March.
Lythrum Cut back to about 15cm during November.
Macleaya Cut back to 15-20cm from ground level during November.
Malva Cut back to about 15cm from ground level during November.
Matteuccia Cut back tatty fronds to ground level in March.
Meconopsis Cut back faded flower stems to near ground level in October, but leave the foliage to protect the crown over winter. Remove leaves in March.
Melissa Cut right back to about 15cm in October and insulate the crown with a layer of dry leaves or chipped bark.
Mentha Cut back tatty foliage in March. Use a sharp spade to cut around the plant and restrict its spread.
Mimulus Insulate the crown with a layer of dry leaves or chipped bark. Cut right back to basal shoots in March.
Miscanthus Cut back during March before new shoots emerge.
Molinia Cut down tall species in November, leave smaller species until early spring.
Monarda Resist cutting bergamot back in autumn since the stiff, vertical stems look good all winter. Cut back to near ground level during February.
Morina Cut right back to near ground level in October and insulate the crown with a layer of dry leaves or chipped bark.
Nepeta Shear off half way during November, then cut back to new shoots near the base in March.
Oenothera Cut back flower stems to about 15cm of ground level during November.
Omphalodes Cut back to about 15cm during November, and insulate the crown with a layer of dry leaves or chipped bark.
Ophiopogon Comb through the plant to remove dead foliage.
Origanum Cut back flower stems to new shoots in March.
Paeonia Cut back herbaceous peonies to near ground level during November. Take care not to tread on new buds at soil level.
Pennisetum Cut back to main clump during March before new shoots emerge. To halt the spread of the plant, remove any unwanted self-sown seedlings as part of routine spring border maintenance.
Penstemon Trim off dead foliage to within 20cm of the ground in November, protect the crown with a layer of dry leaves or chipped bark. Trim back to near ground level in March.
Perovskia Shear off flowers in November. Cut back to a balanced framework 30-45cm above ground in March.
Persicaria Cut back to about 15cm during November.
Phalaris If not already done, cut back all but the youngest shoots to10cm of ground level in October.
Phlomis Cut back stems to about 30cm of the ground during November.
Phlox Cut back to near ground level during November. Clear away dead leaves to prevent carryover of disease.
Phygelius Remove flowers in November. Cut back whole plant to about 15cm in March.
Physalis Cut back to about 15cm of the ground during December.
Physostegia Cut back to about 15cm of the ground during November.
Phytolacca Cut back to near ground level in November. Always wear gloves since all parts of the plant are poisonous and a potential skin irritant.
Platycodon Insulate the crown with a layer of dry leaves or chipped bark. Cut right back to basal shoots in March.
Pleioblastus Cut back tatty stems to near ground level in March and thin others as necessary.
Polemonium Cut back to near ground level during November.
Polygonatum Cut back to near ground level during November.
Potentilla Cut back herbaceous species to about 15cm during November.
Primula Remove tatty foliage in November.
Prunella Cut back to about 10cm during November.
Pulmonaria Remove dead and dying foliage during March.
Rheum Cut back to near ground level during November.
Rodgersia Cut back to near ground level during November.
Rudbeckia Cut back to near ground level during November, protect the crown with a layer of dry leaves or chipped bark.
Salvia Borderline hardy varieties should trim and have their crown insulated with a layer of dry leaves or chipped bark in October. Hardy varieties can be tidied up in March.
Sanguisorba Cut back tatty foliage in March. Prevent plant spreading by trimming around crown with a sharp spade.
Saponaria Cut back to about 15cm of the ground during November.
Sasa Cut back tatty stems to near ground level in March and thin others as necessary.
Saxifraga If not already done, remove faded flower stems to near ground level in October.
Scabiosa Cut back faded flower stems to their base in October. Insulate the crown with a layer of dry leaves or chipped bark
Schizostylis Trim off faded flower stems to their base in November, in cold gardens protect the crown with a layer of dry leaves or chipped bark.
Scrophularia Cut back faded flower stems to 15cm in November.
Sedum Cut off the stems at the base in March, taking care not to damage any emerging buds.
Senecio (herbaceous)Cut back faded flower stems to their base in November.
Sidalcea Cut back to about 15cm of the ground during November.
Silene Cut back faded flower stems to about 15cm of the ground in October.
Sisyrinchium Cut back flower stems to their base during October, earlier if self-seeding is a problem.
Smilacina Cut back to near ground level in November.
Solidago Cut back to near ground level during November.
Stachys Remove dead and dying foliage during March.
Stipa Cut back foliage in February before new shoots appear.
Stokesia Cut back to about 15cm during November.
Symphytum Remove dead and dying foliage during November. Always wear gloves since all parts are a potential skin irritant.
Tellima If not already done, cut back faded flower stems to their base in October.
Thermopsis Cut back faded flower stems to about 15cm in October.
Teucrium Cut off faded flower stems to their base in October. Cut half way back to main clump in March.
Thalictrum If not already done, cut back flower stems to their base during October. Cut back the plants half way to main clump in March.
Tiarella Shear off faded flower stems in October.
Tolmiea Remove dead and dying foliage during March.
Tricyrtis Cut back flowering stems to about 15cm during November. In cold areas of the country provide a deep, dry, winter mulch around the crown of the plant.
Trollius Cut back to near ground level during October.
Valeriana Cut back faded flower stems to about 15cm in October.
Veratrum Cut back flower stems to their base during November.
Verbascum Cut back flower stems to their base in November.
Verbena Cut back V. rigida and V. bonariensis to about 15cm in October and insulate the crown with a layer of dry leaves or chipped bark. In cold areas, lift roots in October and overwinter in boxes placed in a frost-free place. Replant in spring.
Veronica Shear back to about 10cm during November.
Veronicastrum If not already done, cut back faded flower stems to their base in October.
Zantedeschia Removed dead leaves during October, protect the crown with a layer of dry leaves or chipped bark.
Zauschneria Cut back flowering stem to about 15cm of the ground in October. In cold areas of the country, provide a deep, dry, winter mulch around the crown of the plant.