Helianthus annuus This unique breed of sunflower grows to 2-3 feet tall and has beautiful, fluffy heads that attract butterflies and birds! Try these great flowers in your garden this spring. Growing Instructions: To grow well, sunflowers need full sun. They grow best in fertile, moist, well-drained with a lot of mulch. In commercial planting, seeds are planted 45 cm (1.5 ft) apart and 2.5 cm (1 in) deep.