The best time to cut back ornamental grasses depends on one thing: whether the grass is deciduous or evergreen. Deciduous grasses turn straw-coloured in autumn and need cutting back every year, ideally in late winter or spring just before the new shoots appear. Evergreen grasses keep their leaves and only need a tidy in spring, combing out the dead foliage rather than cutting the clump down. Get the type right and the rest is easy.
The short answer
| Deciduous grasses | Leave them standing through autumn and winter, then cut all the old growth close to the ground in late winter to mid-spring, before new shoots come through. |
|---|---|
| Evergreen grasses | Do not cut them down. In spring, pull or comb out dead leaves and old flower stems by hand and leave the healthy green foliage in place. |
| Pampas grass | The exception among evergreens: it can be cut back hard in late winter or early spring, wearing thick gloves and eye protection. |
| Autumn | Not the time to cut. The seedheads feed birds, the stems shelter insects, and the old growth helps protect the crown from cold. |
Deciduous or evergreen grasses: which have you got?
The RHS splits ornamental grasses into two care groups. Deciduous grasses do not necessarily drop their leaves; instead the foliage dies and turns golden or straw-brown in autumn, and that dead growth stays on the plant until you remove it. Evergreen grasses, and grass-like evergreen sedges such as Carex, keep living leaves all year and usually just need a quick tidy.
If you are not sure which you have, look at the clump in late winter. A deciduous grass is all one colour, pale and dry from top to bottom. An evergreen grass still has green, flexible leaves among the brown ones. Some plant labels and the RHS plant pages also state the foliage type.
Deciduous grasses: cut back to the base
Deciduous ornamental grasses, such as Miscanthus, Calamagrostis, Molinia and Hakonechloa, need all their old stems and foliage removed each year so that the new growth can come through unhindered. The timing is early to mid-spring for most, depending on the species, and the key rule is to cut before new shoots emerge from the base.
Evergreen grasses: comb out, don't cut down
Evergreen grasses don't always respond well to hard pruning, so cutting them to the ground can leave a bare, slow-to-recover clump. In early spring, pull out dead leaves, old flower stems and debris by hand, or comb through with your fingers or a rake. Snip off any dead leaves that are firmly attached, and leave the living green foliage alone. Carex, Festuca glauca, Stipa gigantea and Anemanthele are all handled this way.
Warm-season and cool-season grasses
The RHS also groups grasses by when they grow. Cool-season grasses, such as Calamagrostis, Deschampsia, Festuca and Stipa, start growing in late winter and flower before midsummer, so they need cutting or tidying early. Warm-season grasses, such as Miscanthus, Panicum and Pennisetum, come into growth in late spring and flower after midsummer, so you have longer to wait. This is why Calamagrostis is cut at the end of winter, while the RHS suggests waiting until mid-March to April for Miscanthus.
When to prune ornamental grasses, by type
This table brings together the RHS advice for the grasses most often grown in UK gardens. Where the RHS plant page and its general advice differ slightly, both are reflected.
| Grass | Type | When to cut or tidy | How |
|---|---|---|---|
| Miscanthus | Deciduous, warm-season | Late winter to spring; the RHS suggests mid-March to April | Cut all the old stems and dead foliage as low as possible |
| Calamagrostis (feather reed grass) | Deciduous, cool-season | End of winter, late January to February | Cut the whole clump to about 2cm above ground with sharp shears or secateurs, then rake out the centre |
| Molinia caerulea (purple moor grass) | Deciduous | Late winter, just before growth starts | Cut down dead foliage and old flowered stems |
| Hakonechloa macra | Deciduous | Late winter | Cut old flowered stems and dead foliage at the base |
| Pennisetum orientale | Deciduous, warm-season | Wait until late April | Cut to the base; until then the old stems protect the crown from cold |
| Pennisetum alopecuroides (fountain grass) | Listed by the RHS as evergreen, but the leaves turn pale brown in winter | Spring | Remove dead foliage and old flowered stems |
| Stipa tenuissima | Deciduous, often evergreen in milder areas | Early spring rather than late autumn | Comb out if there is little dead growth; cut back fully if there is a lot |
| Stipa gigantea (golden oats) | Evergreen | Spring | Remove dead leaves and old flowered stems; don't cut the clump down |
| Deschampsia cespitosa (tufted hair grass) | Evergreen | Early spring, before growth resumes | Cut the old flower stems to the ground; leave the evergreen leaves |
| Anemanthele lessoniana (pheasant's tail grass) | Semi-evergreen | Early spring | Comb out dead and winter-damaged leaves |
| Carex (sedges) | Typically evergreen | Spring | Pull or comb out dead leaves by hand; keep the green foliage |
| Festuca glauca (blue fescue) | Evergreen | Spring | Comb out dead foliage and trim off damaged leaf tips |
| Cortaderia selloana (pampas grass) | Evergreen | Late winter or early spring | Cut back as far as you can without damaging new growth, using loppers; thick gloves and eye protection |
Why leave grasses standing over winter
It is tempting to tidy grasses in autumn along with the rest of the border, but there are good reasons to hold off.
- Wildlife. The seedheads feed seed-eating birds such as finches, and the standing foliage shelters insects and other small creatures through the winter.
- Frost protection. The old stems help protect the crown of the plant from cold. The RHS specifically advises leaving Pennisetum orientale until late April for this reason.
- Winter interest. Grasses give a border structure and movement when little else does, and the plumes of grasses like Calamagrostis look particularly good in low winter sun or laced with frost.
I'd always rather leave a grass standing a few weeks too long than cut it too early. The one thing to avoid is leaving it so late that you cut through the new shoots.
Timing in colder gardens: check the frost dates first
A month on the calendar is only a guide. Grasses wake up when the weather warms, so the same Miscanthus can be ready earlier in a mild, sheltered garden than in a cold, exposed one. The most reliable signal is the plant itself: part the old stems at the base and look for green shoots. When they start to show, it's time to cut.
In the North East, spring can arrive at very different times a few miles apart. From 30 years of Met Office records, the typical last spring frost is around 25 March in Hartlepool on the coast, 16 April in Peterlee and 2 May in Durham city. In a colder garden there is no rush: leaving the old growth on a little longer keeps the crown protected while frosts are still likely. If you are unsure how late spring comes to you, you can check the frost dates where you live by postcode before you plan your spring jobs.
This matters most for grasses that are less hardy. The RHS rates Pennisetum alopecuroides H3, hardy in coastal and relatively mild parts of the UK, so in a cold inland garden it is worth keeping its old foliage on until spring is properly under way.
How to cut back ornamental grasses
Tools
- Sharp secateurs or shears for most deciduous grasses
- Loppers for the tough stems of pampas grass
- A rake, or just your fingers, for combing out evergreen grasses and clearing debris
- Gloves, and eye protection for grasses with sharp leaf edges such as pampas grass
Cutting back deciduous grasses
- Check the base of the clump for new shoots; aim to cut just before they appear.
- Work through the clump with sharp secateurs or shears, cutting the old stems as low as you can. For Calamagrostis, the RHS suggests about 2cm above ground level.
- Pull out any loose stems and rake debris out of the centre of the clump.
- If new growth has already started, cut above it rather than through it.
- Weed around the plant and add a mulch (see below).
Tidying evergreen grasses
- Wearing gloves, run your fingers or a rake through the clump to pull out dead leaves and old flower stems.
- Cut out any dead leaves that are firmly attached, one by one.
- For Festuca glauca and similar dense clumps, clear the dead leaves that gather at the base and trim brown tips.
- Leave all the healthy green foliage in place.
Pampas grass
Pampas grass, Cortaderia selloana, is the one evergreen grass the RHS recommends cutting back hard each year, in early spring. Cut as low as you can without damaging the new growth, using loppers for the tough stems. The leaf edges are sharp, so wear thick gloves and eye protection. Don't set fire to the clump to clear it: burning can damage the crown.
Mistakes to avoid when cutting back grasses
| Cutting evergreens to the ground | Most evergreen grasses don't recover well from hard pruning. Comb them out instead. |
|---|---|
| Cutting too early | An autumn cut removes winter food and shelter for wildlife and exposes the crown to cold. |
| Cutting too late | Once new shoots are up, cutting low damages them. Cut above the new growth if you've missed the moment. |
| Skipping gloves | Many grasses have sharp leaf edges; pampas grass needs thick gloves and eye protection. |
| Burning pampas grass | The RHS warns this can damage the crown. |
Dividing ornamental grasses
Spring, once you have cut back, is also the time to divide congested clumps. Division keeps grasses vigorous, improves airflow, and is the easiest way to make more plants. A grass that has stopped flowering may simply need more light, but a congested clump can also be the cause.
| Group | Examples | When to divide |
|---|---|---|
| Cool-season grasses | Carex, Calamagrostis, Deschampsia, Festuca, Hakonechloa, Molinia, Stipa | Late winter to early spring, as they begin to grow; may need dividing every few years |
| Warm-season grasses | Miscanthus, Panicum, Pennisetum, Cortaderia | Late spring, around May, when they are in active growth; needed less often |
- Lift the clump with a spade. Large, heavy clumps may need two people.
- Push two forks into the centre back to back and lever them apart, or cut through the clump with a spade. Very tough roots may need a sharp knife or a saw. Small grasses such as Hakonechloa can be pulled apart by hand.
- Keep the divisions as large as you can.
- Replant pieces more than 12.5cm across straight back in the garden, firm them in well and water if the soil is dry. Pot smaller pieces in peat-free John Innes No 2 compost to grow on.
- For pampas grass, cut the foliage down first and wear sturdy clothing and gauntlet-style gloves.
Dividing is also a good moment to rethink where a grass sits. If a clump has struggled in heavy clay or an exposed spot, it may do better elsewhere; my guide to plants for clay, shade and coastal wind explains how to read your garden's conditions before you replant.
After cutting back: mulch, not feed
Established grasses rarely need feeding on most soils. A mulch of organic matter such as garden compost, at least 5cm (2in) thick, is usually enough, and it gives the crown some frost protection too. The RHS suggests mulching between late autumn and late winter (November to February), so if you mulch straight after cutting back in late winter, keep it clear of any emerging shoots.
