Answer: You'll want your sunflowers to develop deep root systems so they can hold their heads up without tipping over. To accomplish this you'll want to water deeply once or twice a week (depending upon weather). Keep the water off the foliage and the stalk to avoid fungal problems. Simply soak the soil beneath the plants, allow to drain then soak the soil a second time. This will concentrate the moisture around the rootmass and ensure they're fully wet.
Best wishes with your sunflowers!
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