10 EARLY MAMMOTH RUSSIAN SUNFLOWER Helianthus Annuus Flower Seeds BLOOM TIME: Late Summer - Fall HARDINESS ZONE: Annual PLANT HEIGHT: 72 - 96" . . . PLANT SPACING: 18 - 24" LIGHT REQUIREMENTS: Sun . . . SOIL / WATER: Average Yellow 12 inch flowers. The Mammoth Sunflower has huge edible seeds. This variety of sunflower has very sturdy stalks and do not require staking. It is the earliest flowering giant sunflower variety.