Tell us what kind of grasses they are, and we can answer intelligently. ;>)

They are: Fountain grass, Blue Festuca, Maiden, and Ribbon. thanks.

Fountain Grass: It can vary, but I'd say to give it at least 2 feet in any direction. As the common name implies, it grows into a fountain shape, much wider at the top than the bottom. There are dwarf cultivars, shich can be spaced more closely.

Blue Festuca: Foliage grows to approximately 1' by 1' and blooms are fine and a bit longer. Give it 18" in each direction.

Maiden Grass: Another one which varies based on clutivar. In general, it's a big tall grass which can easil hit 6-7' to the plumes, and most will grow wider and wider each year. Give it at least 3' in each direction.

Ribbon Grass: This can reach 5' in height, depending on the cultivar and conditions. If it's a straight green variety, it can be a very agressive spreader...almost invasive. Variegated forms are less so, but still spread actively. I'd consider planting this one either in a container, or someplace where physical barriers will contain it, like between a building and a sidewalk.