Homemade pots in tanks

I made a pot and carved it to look cool. I wanted to put HM in it. At this time I really only grown Crinums and moss. I have not had a need (yet) to change to soil. I wanted to add something into the pot that would hold the roots of the HM. What would you use? I would not need much. I am going to try to trim and keep a neat shape with the HM without the spread or long stems. My tank is always in flux and the pots would let me grow or try plants and then move them to where they might work best.