While using a limited number of colors is a plus in a flower bed, planting in shallow rows that top out at a single height is a major negative. When planning beds, go deep—4 to 5 feet front to back, if possible. Then place plants according to height, with the tallest in back, medium-height plants in the middle, and the shortest ones in front. The effect of this layering approach: a profusion of blooms. Stepping down plants by height also lets you reach back rows more easily for deadheading. And such dense planting helps crowd out any weeds. Here, primary colors of yellow, red, and blue look lively but not riotous thanks to the small size of the yellow and red flower heads and lots of green foliage. Soft blue-green lambs’ ears in front provide the third element, and the bonus of fuzzy-leaved texture.