There are plenty of things you could grow in that size, the problem I would foresee is that if they are fabric they could dry out a bit easily as they are losing water all around and not just from the soil surface. Standing them close together and touching in a group would help, the ratio of surface area to volume changes dramatically as you get bigger. They are a good way to grow things on a hardstanding, like a concrete yard, and if you stood them close on a bit of weedy ground it would be just about weed free by the end of the season.