Insufficient Sunlight
A surprise to some, sunflowers really do need full sun—at least six to eight hours daily—to fuel their rapid growth and heavy blooms. I once tucked a row along the north side of my shed, hoping they’d brighten a shaded spot, only to end up with pale, leggy stems reaching desperately for every stray ray!
Relocate sunflowers to the brightest area of your garden, away from tall trees or buildings that cast afternoon shadows. If true full sun isn’t possible, consider dwarf or branching varieties that tolerate part-sun locations better, though they’ll still reward you with lively, pollinator-friendly flowers when given ample light.