Flower beds should never be flat. They should be sculpted and made slightly higher in the center. Each flower bed that I create, if it is not on a slope, is “crowned” with a gentle slope down to all sides. This is very similar to the profile of a street where the center of the road is higher so that rainwater drains down to both sides of the road.
The basic principle here is to let water penetrate in the soil but to drain the excess water slowly away. If the surface is flat, then the water will remain and puddle in the low places. The result is that the flowers planted in these low areas may suffer from too much water accumulating around their roots. The key is to let water drain off. Crowning the bed is the best way to accomplish this.
You will need a sufficient amount of soil to make a plant bed higher in the center by a few inches. Do not skimp on this part. If you do not have an adequate quantity of good topsoil on hand, you must get it from another place on your site or bring it in. This is when the task of crowning a plant bed becomes a real chore. Using quality soil is a must. Know where your topsoil is coming from! I cannot stress this enough. Do not bring in “fill” dirt or phony “topsoil” created from silty “pond bottom” soil. I know it is tempting not to crown a bed, but all I can say is that you will get the best results if you do. It is all about the soil—its quality and how you grade it.
When creating a flower bed, make sure the center is higher than the edges. Use a spade for edging. It has a sharpened, flat edge designed for cutting through soil and roots. It is the perfect tool when a clean line and precise angle are needed. Edge the bed after you have contoured it to a crown, as shown here.