If you put sunflowers in a vase, always cut a piece of the stem first and put them in hot water first.
Sunflowers, first slant cut and then put in HOT water. Thus they will stay fresh longer.
Sunflowers put in hot water with very little splash of bleach.
A vase filled with 10 cm of the hottest water that comes from the tap. After 20 min., The vase during filling with simply, "cold" water from the tap. They do not hang.
Sunflowers are a tasty morsel for snails. It helps to lubricate the edge of the pot in which you have planted the sunflower with Vaseline, here come the snails from over.