This year I purchased extra-large self-watering planters, hoping to help my "Patio Princess" tomatoes survive the extreme weather of the midwestern prairie (Zone 5). But all of the plants in these (very expensive) planters were stunted, with poor root growth. The tomatoes I planted in felt bags, using the same top-quality bagged potting soil, are still thriving, while I tossed out the purple-leaved tomatoes in the pots today. What could have gone wrong?