When I am picking out plants, whether I'm planting them at home or selling them at the shop, I usually buy one gallon containers in multiples of three. Generally they are perennials (plants that come back year after year) so I want them to make an permanent statement in the garden. One plant is often lost - three plants (I usually plant in a triangle as opposed to a row) will grow together and make more impact.
Here is a huge row of beautiful deep red geraniums. As you can see there are only a few blooms. This is actually the ideal stage to buy plants. I prefer one bloom so that you know what color you're getting with lots of buds. If you buy a plant at the nursery that is covered in blossoms more than likely you've already missed the show and you will get few new blooms after you take it home. So next time you're at the nursery look for buds - not blooms!