Helianthus annus flower seeds. Red Sun is a branching variety of Sunflower, which produces vibrant red petals, accented with a dark brown center. Each plant will grow to a mature height of roughly 5 to 6 feet tall, and will produce 5 to 6 inch bloom Germination takes 10-14 days. For outdoor sowings from April onwards, sow 1.5 cm deep directly into well raked, moist soil and protect well from slugs and snails. Growing: Grow the seedlings on repotting as necessary and plant out when they are about 30cm tall in a sunny spot price is for 20 seeds