In the spring do you cut down ornamental grasses?

Yes, ornamental grasses should be cut or clipped to the ground in late winter/early spring, just before they begin putting on their new growth. Waiting until later to cut them will not inhibit their new growth. Cutting back old growth will clip the new growth leaving straight edges on the new growth blades.

They can be pruned back in fall, too. Waiting for late winter/early spring allows the birds and other wildlife to eat the seeds from the plumes and ornamental grasses are attractive garden plants for winter interest.