Seeds germinate in 5 - 10 Days Plant seeds at a depth of 1 inch Plant seeds or seedlings 2 to 4 feet apart Grows to a height of 9 - 12 feet. Blooms from Mid-Summer to Fall Mammoth Gray Stripe Sunflower Seeds have enormous yellow flowers that measure 14 inches across and yield a whopper crop of seeds! They have a high oil content that makes for great roasted flavor. Matures in 100 DAYS.