What is this plant

[Worksforme]

My DM bought this plant years ago for £120 and was told it wouldn’t spread. It does. Until she can find out what it is she doesn’t know how to prune it. Any ideas?

It’s about 6ft tall and 3ft across. It doesn’t flower but dances in the wind!

Tamarix? www.rhs.org.uk/plants/details?plantid=1905

I don’t think it’s tamerix as there are no flowers, also not cane grass.

I think it is some sort of ornamental grass or sedge but other than that, can't help sorry.

Possibly miscanthus? Certainly an ornamental grass.
I'm not sure when they can be cut but I know that they can be cut right back.
Maybe try the RHS website and search ornamental grasses - should narrow it down a bit.

Yup miscanthus for me. Your Mum is lucky, mine all Peter out.

it can be lifted when dormant , oct- feb , and split/ divided and replanted.

I don’t think there’s enough info in that picture to say “Miscanthus” although that’s certainly widely planted. OP, are you sure there are no flowers? There should have been a stage when the bits which now look as if they have seeds had little furry strands a few mm long sticking out, or perhaps little bits of dandruff - that was the flowers.

It should have long narrow leaves, with parallel veins. If you follow the leaf back down to the stem, the leaf wraps itself round the stem as a sheath, and between the sheath and the rest of the leaf, there’s a dividing line, with a tiny ligule - a little flap which could be a tiny collar, a long tongue, a ragged bit of membrane or even just hairs. If you can see that lot, then it’s certainly a grass of some kind and can be treated accordingly.

If you google images of “Miscanthus ligule” there are some clear pictures of what I’ve described

Looks like some kind of Restio from South Africa. Family Restionaceae, which is related to the grass and sedge families.

They'll be the flowers in your second photo. I've seen them for sale from specialist nurseries at shows but never grown them. Your DM's plant seems to be thriving.

I wouldn't think they need any pruning of the top growth other than removing dead stems. Might need its rhizomes chopped back if it's spreading too much.