Sunflowers need plenty of watering and sunlight, taking approximately two weeks to appear and 90 days to fully grow. If using chemical weed killer, make sure it is suitable for use on sunflowers or pull weeds out by hand. Over-watering sunflowers will likely damage flower heads, particularly 20 days before or 20 days after full bloom.
Pour around 2 gallons of liquid fertiliser solution each week around the roots of the sunflower, taking care not to pour the solution over the stem as this has been found to cause sunflower stems to rot. Read more