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I planted two miscanthuses in spring 2019, but I didn't have time to cut them back in March this spring (three or so inches above ground, as almost universally recommended).

In April, I gathered, it was too late, it already started growing, so I left them as is.

However, they grew without problems and reached over 6 ft this year (as opposed to 5 ft last year). Old stuff just fell off naturally. What is than the deal with cutting them back in early spring/late winter? Is it really needed?

Aleksandar M
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  • This is not an answer, but a caution. Depending on where you live, miscanthus could be a highly invasive pest. On Long Island, NY, some towns have banned its use in landscapes because it produces lots of highly mobile seeds and winds up growing in meadows and forest edges, displacing native plants. While sometimes not quite as showy, there are a number of native grasses that can be used in its place. Panicum virgatum and Sorgastrum nutans come to mind - both of which would also have great benefits to native birds and mammals. Miscanthus is very difficult to eradicate. – That Idiot Oct 05 '20 at 10:25
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    Well, what can one do, there is no ideal plant. But, invasiveness is not the same for all continents. In Europe, where I live, there is much less problems with miscanthus than in north America (the reason could probably be less frequent usage). Another example is Norway maple, which is in Europe quite peaceful tree, while, in my understanding, is considered dangerously invasive in US. Nature is so strange. @That – Aleksandar M Oct 05 '20 at 14:20

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It appears cutting back is needed solely for aesthetics purposes.

I base my answer on this web page (PRUNING MISCANTHUS), that says:

In nature, nobody prunes deciduous grasses. New leaves simply emerge through old, tired ones and eventually cover them up. And the old leaves eventually decompose and disappear, usually the same year. Remember too that the very best compost for any plant is its own dead foliage! Allowing the old foliage to remain intact will slightly slow down the speed at which the grasses seem to green up, but in no way harm them … and an unpruned plant will soon catch up to a pruned one.

If your ornamental grass is in the back of the garden, where the transition period—where you see a mixture of green and brown leaves (which can last up to mid-July)—is not so visible, you can simply walk away and let the plant take care of itself.

In spots where the grass is highly visible, however, you may want to cut the grass back in early spring.

Aleksandar M
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We inherited a stripy miscanthus when we moved into our current house a few years ago. It hadn't been cut back for goodness knows how long, was full of dead stuff, looked tired and a bit of a mess. I chopped it back, mulched/fed it and was rewarded with a much improved plant with lots of fresh, attractive young growth. Here's a photo taken today (5 October) seven months after its annual trim.

Miscanthus

Peter4075
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  • Thanks for sharing your experience, but where are flowers/seeds in the picture? They are usually very distinctive at this time of year, should be in the center, the highest part of the plant, like this: https://images-na.ssl-images-amazon.com/images/I/61IvbGrLJtL._AC_.jpg Is yours some kind of sterile one? – Aleksandar M Oct 05 '20 at 15:54
  • @AleksandarM - early November and the flowers are just starting to appear. – Peter4075 Nov 06 '20 at 12:50
  • Probably a matter of climate and cultivar. My "Gracillimus" already flowered in summer in zone 7. @Peter4075 – Aleksandar M Nov 09 '20 at 18:35