So sorry, by a foam container I meant the lightweight pots that look like clay but are really plastic. So any container that does not heat up as clematis like cool roots. You can successfully grow clematis in a clay or even metal container as long as the pot is always in the shade. Clay containers dry out quickly in the sun and warm the soil so a plastic (some are made of thick plastic much like foam) or glazed ceramic containers help to insulate the roots in a sunny site. Just make sure any container you use has drainage holes. Add more drainage holes if there is only one small hole as the clematis roots can clog a drainage hole in just a few years. You are the way to a beautiful clematis garden, thanks for coming to class. Keep growing, Marianne Binetti