Ornamental grasses: cutting back
Ornamental grasses fall into two main groups, evergreen and deciduous. Deciduous grasses need cutting back annually so that they will look their best. Evergreens just require a tidy-up.
Timing: Early to mid-spring
- Deciduous grasses can be cut back hard
- Evergreen grasses usually only need the dead material removing and do not always respond well to hard pruning
When to cut back
Early spring to mid-spring depending on the species.
How to cut back
Deciduous grasses, which turn a golden, straw brown rather than necessarily lose their leaves, need different treatment from those with are evergreen.
- Some deciduous species, for example Calamagrostis × acutiflora 'Karl Foerster' and Deschampsia cespitosa 'Goldtau' should be trimmed to ground level before growth starts in early spring. Other deciduous grasses, such as Pennisetum orientale, do not produce new growth until later in the season. The culms (old stems) will protect the crown, so delay clipping these types until late April
- Pruning late (mid-March to April) is also appropriate for Miscanthus, which has structural stems that persist over the winter. These should be pruned away individually with secateurs to ensure the new, green shoots are not cut off in the process
- Stipa tenuissima is classed as deciduous but in some gardens performs more as an evergreen. If the build up of dead material is low, treat as for evergreens by simply combing out the loose foliage. Alternatively, and for plants with a lot of dead, cut back fully in spring
- Small evergreen grasses, such as Festuca glauca, can be trimmed in spring. Remove any brown tips and cut back the dead leaves that usually collect around the base
- Larger evergreen species such as Cortaderia selloana (pampas grass) benefit from hard annual pruning in early spring, cutting back as far as possible without damaging new growth. Wear goggles and thick gloves as leaf blades have sharp edges, and cut tough stems with loppers. Burning pampas grass is no longer common practice as the crown can be damaged. Removing a large unwanted pampas is no easy matter and may require machinery such as a mini-digger if digging around with a spade or mattock fails to lift it
- Evergreens such as sedges (Carex and Luzula) are not cut back completely like deciduous grasses. Spent flowering stalks can be cut off, and any unsightly scorched or diseased leaves can be removed individually
- Once the clump outgrows its space, you can divide it as you would any other perennial. Debris can be removed, the area tidied, and mulched with organic matter and fertiliser spread as for deciduous grasses
Step-by-step pruning of deciduous grasses
- There are three plants in this clump. The dead leaves and flowering stalks have been left uncut over the winter. It is now ready for cutting back, before the new growth comes up in spring
- Cut back the spent stems with secateurs. Take care not to damage any new growth that may already be coming up through the crown of the plant. Stems and debris can be pulled out by hand from the centre of the clump
- The grass is now half-way cut back; it is easier to see what you are doing, and to avoid damaging any young green shoots coming up through the lower part of the clump
- You can now cut the clump back to a few centimetres from ground level, leaving a hairy tuft through which the new growth can come up easily without getting tangled with the old stems. Pick out any dead leaves or debris from the crown of the plant, and remove any weeds
- Tidy the surrounding area. You may wish to mulch and top-dress around the crown with 50g per sq m of a general fertiliser. This will feed the plant as it comes back into growth, and freshen up its appearance before the spring
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