In my neck of the US sunflowers grow tall and die before October, not the best for a "cover crop" description.
It seems to me like sunflowers are highly allelopathic. So growing them as a cover crop would tend to supress germination of crop species and/or interfere with growth.
Gilbert Fritz wrote:Joseph, how long does this effect last? I know rye is allelopathic, but that makes it a better cover crop; it suppresses weeds, and the effect breaks down in about six weeks. Does the sunflower effect last longer?