Do I need to kill the grass or till the soil before starting a raised bed?

Question:

Do I need to kill the grass or till the soil before starting a raised bed?

Answer:

Before filling raised beds, remove the grass sod, if possible, and work up the existing soil with a rototiller or spade.  Add a few inches of the soil mix, then incorporate it into the existing soil.  Continue to add and incorporate additional soil mix until the raised bed is filled.  Incorporating the soil mix into the existing soil prevents the formation of distinct layers in the raised beds.  Distinct layers of soil impede water movement and discourage root growth.