Clay soil is often cursed by gardeners but clay can be a wonderful thing. The Dirt on Dirt - Clay will teach you about clay soils, why you should love them, and how to make them even better.
Any soil can benefit from adding organic matter. To learn more about transforming bad soils to good and making good soils even better read this article.
Learn how your choice of container and soil and correct watering and fertilizing practices will produce great planters.