Decorative angel hair (Stipa tenuissima), also called feather grass, in any case should not be cut back too early, otherwise moisture and cold can harm the plant.
Old stalks protect from water, cold and frost
Ideally, we cut back the feather grass when strong night frosts or long periods of frost can be ruled out. Therefore, I myself usually cut back the grass from mid-March to early April.
In any case, the grass should not be cut back before the winter months. Moisture could otherwise accumulate at the root ball due to the lack of foliage, freeze there and thus harm the plant.
Already after a few days after cutting back, we see that new green sprouts from the cut stalks, you can literally watch.
Support growth with grass fertilizer
To help the plants quickly rebuild their lush foliage, I fertilize the soil of the grasses immediately after cutting. This is easily done and provides the plant with nutrients for the coming season. I always use the Bamboo and Ornamental Grass Fertilizer from Dehner (Amazon affiliate link).