Answer: Sunflowers are annual plants so once they have flowered and set seed, the plants will die. What you describe is normal for sunflowers. As the flowers begin to set seed they become heavy and instead of facing the sun, they lean down towards the ground. This serves two purposes: it protects the seeds from rainfall and if you did not harvest the heads to collect the seeds, the leaning over would allow the seeds to drop onto the ground where they could germinate and grow into new plants next spring. You can tell when the seedheads are mature enough to harvest by watching the back of the head. When it turns from green to a tannish color, the seeds are ripe. You can cut the head off the stalk and set it in a protected spot to finish drying. I put mine on a bench in the garage - just to keep the birds from feasting on the seeds. After about a week, rub two seedheads together and the sunflower seeds will pop right out.
After harvesting the seedheads, dig the old stalks out of the garden.
Enjoy your sunflowers!
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