Lilies ("Lilium") grow from bulbs composed of overlapping fleshy scales. These bulbs never go completely dormant and do not form a protective tunic unlike tulips or daffodils. Instead the overlapping scales help to ensure the survival of the "heart". Even if outer scales are damaged or broken it will not hurt the interior structures.
A broken scale is capable of asexual reproduction by producing small miniature clones called bulblets. This is the bulb's natural way of ensuring it's survival if damaged by rodents or an overzealous gardener for example.
Growers can also benefit from this defense mechanism by purposely removing a few outer scales for propagation without damaging the mother bulb. This is a better technique than dis-sectional cuttings of tunica bulbs, for example, where the mother bulb is sliced into pieces.
Getting the Scales
When you buy lily bulbs make sure you remove a few outer scales from each bulb before planting. You can generally remove several scales with no adverse effect. Use name tags as it will take 2-5 years to remember which scale belonged to which lily.
You can also dig up an existing lily bulb, preferably in late fall after the flower stem has died back and turned brown. Alternatively, you can dig a hole next to a growing lily, without removing the bulb from the ground. Gently work your way down to where the bulb is planted and break off a few scales from one side. This technique works great in a neighbor's yard.
Breaking off the scales
Make sure you get a piece of the basal plate which is the hard material at the bottom of the bulb where all the scales are attached and from where the roots grow. The basal plate is stem tissue where the bulblets will form.
You can use your thumb to gently push one scale away from the bulb. Insert the fingers in the gap and break the scale off as low as you can. You can also insert a short, sturdy knife between the bulb and the scale and cut straight down through the basal plate. The individual scales should have a slight discoloration at the bottom which is, in fact, portions of the basal plate itself.
