Organic Mammoth Grey Stripe Sunflower Seeds. 90 to 110 days to maturity. Helianthus annuus. Heirloom, Non-GMO, Annual. Mammoth sunflower seeds grow one of the tallest, brightest, and most breathtaking flowers in the world! Mammoth sunflower seeds grow an unbelievable 9 ‚12' tall and world famous for their stunning 12‚ blooms. ~ 400 Seeds/ounce.