Consult this chart for optimal, even spacing
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.