(Allium ampeloprasum) Onion relative that does require a long season, but is otherwise very easy to grow. Start the tiny seeds indoors in early spring, setting out anytime after the hard frosts are gone—seedlings can tolerate a few degrees of frost with no difficulty. Give leeks the richest possible soil. As the plants start to become really large, earth up soil or mulch, covering the stems, which then blanch or turn white, which is considered to improve the flavor. Mulched leeks do tolerate cooler autumn weather but should be lifted and stored before bitter cold arrives.