Sunflowers grow best in locations with full sun. They are remarkably tough and will grow in any kind of soil as long as it is not waterlogged. They do fine in soils that are slightly acidic to somewhat alkaline (pH 6.0 to 7.5). Once sunflowers get started, they can tolerate drought as befits plants whose ancestors grew happily in dry prairie regions. They are so easy to grow that they often plant themselves, springing up unbidden beneath a bird feeder.
Sunflower seed, leaves and stems emit substances that inhibit the growth of certain other plants. They should be separated from potatoes and pole beans. Where sunflower seeds are regularly used as bird feed, toxins from the accumulated seed hulls eventually kill the grass below. Harmless to animals or people, the toxins eventually biodegrade in the soil.