Petco was selling wheat grass packaged as "pet grass" in little pint-sized containers. No dirt, just a tightly woven root ball. My guys love this stuff and it looks great. I don't know how long it will last in the tank, but I was able to pull the roots apart & make three nice sized plantings out of it. They climb all over it and nibble on the blades of grass. At the base of each blade is a wheat seed where the seedling grew, and a few of them seem to love munching on those too.
Sadly, although it looked great & my hermies LOVED it, it didn't last long in the tank. I'd suggest using it as more of a food source as a treat and not an actual plant. I wouldn't suggest leaving the plant in the tank for more than a week in the spring & summer months. The plant was still looking good after a week, some of the leaves did start to yellow & became a breeding ground for fruit flies.
It was marketed for cats, lizards, dogs etc.. It's nice for a treat, but don't expect it to live & grow in your tank. Think of it more like produce.. mine lasted about 2 weeks. I'd have taken it out sooner if I knew it would attract fruit flies when it started to wilt.