Purple Pampas grass
I grew some from seed in central Wisconsin. How do I take care of it for the winter. It is in two pots now.
You need to select containers that are large enough and have enough volume of good-quality container soil mix to support these grasses. And then be sure to select plant materials that are a zone or two hardier than the zone you live in, as being above ground makes them 1 to 2 zones less hardy.
Good drainage is also necessary as is making sure they get adequate water up until the soil freezes in the planter. The materials that your planter is made up of has a direct connection to the weatherization of it. Composite plastics, metal, and concrete are the most durable, long lasting, and can resist temperature fluctuations. You then line the inside of the container with a 3″ thick Styrofoam.
Mulching the containers in the fall will also help insulate the plant materials and provide moisture retention. And if possible, for winter, group the containers together in a sheltered spot or even in a garage or shed.
You can even wrap them all in bubble wrap to provide additional insulation.