How to trim ornamental grasses: when and how to prune the different types

Finding out how to trim ornamental grasses means first establishing what type yours is. Many varieties only need minimal pruning and cutting back, while other types need a hard chop to tidy them up. Whichever option is right for your ornamental grass the good news is that it's easy to do, which makes them a top choice if you’re after a low-maintenance option. 

Evergreen grasses are the easy option as they can be left to get on with it all year-round apart from occasionally removing any dead foliage. Meanwhile, the deciduous varieties of ornamental grass tend to fizzle out at the end of summer when their foliage turns brown and straw-like, so they will need cutting back hard once a year to keep them looking their best. There are also semi-evergreen grasses to add to the mix.

Knowing the optimum pruning time is a key part of learning how to grow ornamental grasses, so make sure you are up to speed with the correct time of year and the right methods for doing it. 

Expert guide on how to trim ornamental grasses

It might seem that autumn is the natural time to tidy up many different types of ornamental grass as part of your fall gardening checklist, but it's worth pointing out you shouldn't be in too much of a hurry. 

'Many ornamental grasses have excellent winter presence, adding beauty and interest, while also providing important cover for wildlife through the cold months,' says Beth Chatto Gardens head gardener Åsa Gregers-Warg. 'The perfect time to cut many of them back is when late winter begins to give way to early spring, before new foliage appears.'

Expert tips how to trim evergreen ornamental grasses

Evergreen ornamental grasses don't require hard pruning. It's more a case of tidying them up rather than getting stuck in with your best secateurs. 'They provide texture, movement, softness, transparency and interest for the winter garden as they look lovely with a hoar frost,' says garden designer Jane Bingham. It's certainly one of the main reasons why gardener Monty Don's favorite ornamental grasses for fall color look so impressive in his own garden during the cooler months. 

'Evergreen grasses such as Deschampsia (Tufted Hair Grass) and Luzula (Snowy Woodrush) keep their foliage in all seasons, so trimming them in the conventional sense is not necessary,' says Morris Hankinson of Hopes Groves Nurseries. Usually, a comb or pull-through in spring is all that's needed. 'Don’t forget to wear thick protective gardening gloves,' adds Morris. 'Some of these grasses are tough and will give you a sharp cut or two on unprotected skin.'

Other popular evergreen grasses that can be tidied in spring include Festuca glauca, and varieties of Carex. Remember that all evergreen grasses are an excellent choice if you like landscaping with grasses as they offer interest year round.

'To keep evergreen grasses like Stipa gigantea and Poa labillardierei looking good cut them back to a neat dome-shape,' says Åsa Gregers-Warg. 'Gently groom to remove any old thatch by running a rake or your hands (wear gloves!) through the grass. As the new growth emerges they look not unlike shaving brushes.'

Follow these simple tips to keep them looking their best. 

1. Start by removing any brown tips and cutting back dead foliage that may have built up around the perimeter at the base of the plant.
2. Spent flowering stalks can be cut off, and any unsightly leaves removed. Comb your fingers through the clump at the same time to sift out any faded foliage. 
3. Water the clump with the spray attachment of the garden hose to freshen it up and water away any loose debris.
4. Apply a liquid fertilizer to your ornamental grass to give the new growth a head start.

How to trim deciduous ornamental grasses in a few simple steps

Popular deciduous ornamental grasses that benefit from hard cutting back as part of your spring garden jobs include Miscanthus, Calamagrostis x acutiflora 'Karl Foerster' and Deschampsia cespitosa 'Goldtau'. They should be trimmed to ground level before fresh growth starts to emerge in early spring. 

Deciduous grasses such as miscanthus, panicum and calamagrostis are cut back to two or three inches from the ground with garden shears or secateurs. 'There are a few exceptions: Pennisetum orientale and P. villosum are slightly more more tender and will come into growth later, so are usually left until mid spring to protect the crown,' explains Åsa Gregers-Warg. 'Grasses like Molinia and hakonechloa die back in fall and as ours are underplanted with early flowering bulbs, we tend to rake away the collapsed stems before Christmas.'

'Deciduous grasses such as Imperata (Japanese Blood Grass) and Chasmanthium (Sea Oats) die right back every winter,' says Morris Hankinson. 'Simply chop them back close to ground level in spring when the weather warms, but before the plants show new growth.'

These simple steps will ensure your deciduous grass looks its best once it bursts into new growth. 

1. The ideal time to trim deciduous grasses is in spring before the new growth shoots up. Your clump of grass is probably not looking it's best at this time as it will be full of dead leaves that have accumulated since last fall.
2. Start by combing through the plant with your fingers to remove any dead foliage that sheds easily. It's a good idea to wear gloves.
3. Next grab loose handfuls of dead stems and begin to cut them back hard with secateurs. This needs to be done carefully so you don't damage any new growth.
4. Tackle the crown of the plant where it forms a clump at soil level and the stems emerge. Again, be careful you don't accidentally snip any fresh green shoots. Aim to cut the clump back to a few centimetres, making sure you get rid of any dead or tired looking old stems. Pick out any dead leaves that may have accumulated in the crown.
5. Now is a good opportunity to clear the clump of any weeds that may have popped up either in it or in the surrounding area.
6. If the clump of grass looks dry given it a quick spray of water to spruce it up and clear away any remaining debris.
7. Now feed your ornamental grass with a general fertilizer to give it a boost as the new growth will start to emerge more freely now it has been trimmed back.

How do you trim semi-evergreen ornamental grasses?

There is another category of ornamental grasses where you need to go with the flow. Semi-evergreen grasses drop their leaves in cold winters but keep them if it is mild, adding interest to your winter landscaping. 

'Semi-evergreen grasses such as Koeleria (Blue Hair Grass) and Stipa (Golden Oats and Pony Tail Grasses) usually keep their foliage right through winter unless it’s very cold in which case they will likely die back,' explains Morris Hankinson. 'In a normal season treat them like evergreens, combing and pulling at any dead leaves and snipping back the old flower stems.' If they die right back after a cold winter then chop them back in the same way as you would deciduous grasses.

Stipa tenuissima is a popular ornamental grass that is semi-evergreen and can easily look scruffy after the winter. 'I was told when I first started working as a gardener not to cut them back too hard as they might die,' says Åsa Gregers-Warg. 'Perhaps this is because we’re on free draining soil in a mild climate here at Beth Chatto Gardens, so they don’t seem to mind the harsh treatment of thatch being pulled out and being trimmed back to a couple of inches from the ground. It’s all about trial and error when it comes to how to trim ornamental grasses as all keen gardeners know.'

What are the best tools for pruning ornamental grasses?

'There are several different tools you can use when pruning ornamental grasses, it really depends on the size and age of the plant,' says Paul Hicks, product manager at Stihl. 

'For small or young plants we recommend using a pair of the secateurs and for mid-sized plants it might be better to opt for a battery powered tool, such as the Stihl HSA 26, which makes light work of the task while also keeping you in control of what you want to remove.'