Styrofoam coolers? I have old coolers from when my mom got frozen meals delivered. They work wonderfully as extra insulation, as they create space between the cold and the plants. I have had to use them, as well as overturned large empty pots (the thicker the plastic the better) to protect my lilies from freezes in late May the last two springs. It looks ridiculous, and I am sure the neighbors think I am crazy, but I didn't lose any lily flowers to freeze. My sister living 3 miles away lost about 2/3rds of her lily tops, which equals 2/3rds of her lily flowers. It is no small task, as I have 50+ clumps to cover.