The proper depth for planting allium bulbs depends on the size of the bulbs, but generally ranges from about 3 to 8 inches. The size of allium bulbs varies by species and can range from less than a centimeter to 8 to 10 centimeters in diameter.
A good rule of thumb is to plant the bulb at a depth that is three or four times the diameter of the bulb. It is important to plant the bulb with the pointed end facing upward. Spacing between bulbs should be anywhere from 3 to 10 inches, depending on the height of the species, but plants should be far enough apart to avoid shading each other. Allium bulbs require fall planting before the ground freezes.