Advice
RHS Help & Advice
How to cut back ornamental grasses
Many people feel unsure how to approach the cutting back of ornamental grasses, as if grasses were somehow different from other herbaceous perennials. They are not. But they can be large, and they are often left uncut over winter, as the bleached stems provide structure, movement, and shelter for wildlife in a season when many plants have died back completely.
Cutting back 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.
Cutting back evergreen grasses
Evergreen grasses are not cut back completely like deciduous grasses.
Spent flowering stalks can be cut off (left), 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 mulch and fertiliser spread as for deciduous grasses.
Maya Albert