Feathery foliage on tall and vigorous dill plants that mature and form seed quickly from large umbels of yellow flowers. Sow Long Island Mammoth dill seeds at the back of the herb or vegetable bed, as plants can reach 2m (6′) tall or more. In fact, it gets so tall, it makes a nice specimen plant, central in the garden. Harvest the leaves as needed. The leaves and seeds dry well.