Garlic and onions do best in light, well drained, but heavily composted soil. Garlic is a gross feeder while it is growing tops, before the bulbs start forming. Stop fertilising once the bulbs start forming, but do not let them dry out until the tops begin to dry off. Bulbs will rot if watered past this point. Top setting garlic should not be watered once the flower stems are obvious, as this will stress the plant causing it to form tight layers of protective skin.