Ornamental grasses come in a lot of types. There are smallish ones and very tall ones.
In some areas, these grasses come back after the winter. All you do in March is cut them down and then wait until they grow again.
The plumes usually show up in the summer. They last a fairly long time. When they dry out, you can cut them and perhaps use them for decoration. I would ask someone who knows if this would be okay and have that person cut the plumes.
In winter, with snow, the ornamental grasses stand out. Even if they are dry and brown, they are plants in a dreary landscape.
To plant an ornamental grass, dig a hole large enough to place the roots into the hole. Cover the roots and tamp down the dirt. Water the roots and don’t let the dirt get too dry for a couple of weeks. That way, the roots settle into their new home happily.
If the ground isn’t frozen, you can plant the ornamental grasses. The time of year isn’t important as it may be with some other plants.