Sunflowers thrive with regular watering. However, daily watering is not a requirement when growing sunflowers. While sunflowers can withstand drought, they tend to grow the best in slightly moist well-drained soil.
Typically, sunflowers require the most water about 20 days before flowering and up to 20 days after flowering. Once the back of sunflowers start turning brown, watering can be cut back. Burpee recommends deeply watering sunflowers to promote a strong root system. Sunflowers with weak root systems are not strong enough to hold up the heavy heads of the flower and are more susceptible to issues such as root rot.