Wo these need to be cut back and if so, when?
Red Fountain Grass
Whether you cut ornamental grasses back in the fall or early spring is up to you. Dormant grasses look nice in a barren winter landscape. However, if you get a lot of snow, grasses can be flattened under the weight. They will not regain their upright form. Leaving grasses intact increases the chance of many seedlings next year unless you remove the inflorescence (seedhead).