Sunflowers grow best in location by chock-full sun. They are amazingly hard and will grow in any sort of soil as long it is not waterlogged. They do fine in loam that are vaguely bitter to somewhat alkaline pH 6.0 to 7.5 Once sunflowers get ongoing, they can accept lack as befits plants whose ancestors grew happily in dried up plain regions. They are so easy to grow that they often plant themselves, springing up unbidden lower a bird feeder.

I'm guessing it has something to do with weather we've been having!