Consult this chart for optimal, even spacing

Bedding plants

Many annuals are suitable for massing in beds to produce a swath of color. Set out bedding plants in offset rows, so that groups of four form diamonds, as shown above; space them as recommended in the individual plant listings or at the nursery. For even spacing, measure the distance between plants with a piece of wood of the desired length. The chart below shows the area that will be covered by a particular number of plants set out at various spacings.

Recommended spacing
between plants
Area plants will cover
 48 plants*64 plants*
4 in.4 1/2 sq.ft.6 sq. ft.
6 in.10 sq. ft.13 1/2 sq. ft.
8 in.18 sq.ft.24 1/2 sq. ft.
10 in.28 1/2 sq.ft.38 1/2 sq.ft.
12 in.41 1/2 sq.ft.55 1/2 sq. ft.
*Plants per flat