One method of dealing with rocky soil is to create raised beds or berms for plants to grow in, above the rocky soil. These raised beds or berms should be at least 6 inches (15 cm.) deep, but the deeper the better for larger, deep rooting plants.
Sunflower roots spread widely and can withstand some drought. However, it is best to water them regularly during their most important growth period which is about 20 days before and after flowering. Deep, regular watering helps encourage root growth, which is especially helpful with taller...