Pay attention to what stays green longer, or gets green sooner, in your area. Most likely if you bought some fancy plant, it wouldn't stay alive in your climate. Plus, the chickens may or. Ay not eat it, since a lot of things that stay green, are tough and brittle. Also, if they did go crazy for it, they would most likely kill it, because it wouldn't have a chance to grow.....
An idea to give them something to do in the winter, is put some soil in there that has decaying leaves, etc. they love to scratch through it. Of course, you would have to do this on a warmer day, when the ground wasn't freezi, which may not be possible. We let our chickens free range all year round. I think it helps with feed costs.