Answer: Ornamental grasses as a rule do grow very tall and wide. By late August they should have reached their maximum size for the season with the exception of the flowering plumes yet to come. Trimming now (or any time in the season) would ruin the natural shape because these grow from the base only, not from the tips. Trimming now would also remove the blooming stems coming up through the top of the plant. Unfortunately, there is no way to control the size of these plants by trimming. You might consider moving it next spring instead. On the other hand, trimming would not kill it. Once frost hits the top of the plant will be killed back to the ground and can be cut off at the base either this fall or early next spring before growth begins.
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