Helianthus Giganteus or Giant Sunflower is a perennial to Zone 3 but is commonly grown as an annual. If you are looking for the biggest and tallest sunflower, you've found it! Reaching up to 16 feet, these huge blooms make perfect competitive flowers. The gigantic blooms are supported on sturdy stocks with large leaves. This specie sports giant flowers with light yellow to gold showy ray florets. They have large, coarse, hairy, and somewhat sticky leaves. The golden yellow flowers with brown smaller flowers make up the center. These towering sunflowers measured in at 12-14 feet tall. The seed head measures up to 15in across or more and is packed with many sunflower seeds. The plants bloom from July to September. These plants are bold, beautiful and easy to grow. This sunflower is used commercially for cooking oil and margarine, and even car oil. In its original home it was originally use for oil, flour and as a dye bye the Native American Indians. Hardiness zones : 3-9(-37c/-35f, -5c/25f). Helianthus Giganteus prefers a sunny place in a well-drained soil, and they are very tolerant of drought and poor soils. If the plants are planted in partial shade, staking may be necessary to support the plants, or the plants can be pinched at planting to promote branching.