Sunflower 'Giant Single Yellow' Seeds 30 Sunflower 'Giant Single Yellow' Seeds £2.00 Out of stock. Helianthus annuus Sow: March to June Flowers: July to September Height: 1.8m+ A fantastic variety for kids – tall, with a single giant yellow flower. Great for wildlife too! Sowing instructions: Sow from March onwards. Sow a few seeds in a pot and thin out until the strongest remains. Germination takes 7-14 days. Pot on when large enough to handle.