I cut the bottoms off of 2L plastic soda bottles, punched a few holes in the bottom for drainage, filled them with soil and planted grass seed in them for our rabbit. I used 2L bottle because I could make them short enough, they are light enough to move frequently, and it was no big deal at all if they got wrecked. (yay for repurposing free stuff!) We currently have a few of the pots on a windowsill, and we give her access to one a day while the others grow back from her nibbling. Once she's "mowed" it (usually in about 20 mins) we remove it from her cage and put it back on the sill so she doesn't kick it over, chew on the plastic, completely destroy it, or whatever.... It's also probably healthier for her not to have moist soil all over her cage. For her, it's a nice supplement, in addition to the other food stuffs we give her, and she seems to really like it. I'm working on a few pots of herbs/leaf lettuce now for her to have access to as well, but I'm not sure if I'll actually put the pots in the cage for awhile, or if I will just clip pieces to give to her. Seems to me she could rip throw the lettuce at lightning speed, ruining the whole plant. Maybe something similar would work for your hamsters?