Answer: Mature sunflower heads get heavy and can pull the stems over after a heavy rain, but the heads are also heavy at the end of the growing season. As the seeds begin to ripen the heads bend downward - to protect the seeds from the elements. This is a natural process and there's not much you can do about it. The rigid stems are somewhat pithy in the center. This is what gives them the strength to hold the heavy heads up. I don't think there was anything wrong with your plants last year. When you plant, expect that they will follow the sun with their open flowers, that the flowers will naturally droop as they mature and that the stalks will be pithy inside when you cut them down.
Q&A Library Searching Tips