Lilies propagate on their own. As part of the plants' design, lilies have underground root structures called bulbs that multiply and cling together onto one main bulb. In time, usually after 3-4 years, it is time to separate the lily bulbs since the garden may be overcrowded and not thriving if too many lilies are using the same water and nutrients. Separate lily bulbs in the fall, but as long as you can physically dig into the ground (it's not frozen), you can divide them in the winter. It may, however, take a year for the lilies to bloom again, so you may want to do only a few clumps at this time.
Prune back the foliage if you haven't done so already. Leave about an inch or two of foliage on each plant.
Lift lily bulbs out of the soil using a garden fork or shovel. First dig a circle around your plants. Then pull the handle down in several places to gently lift the lily bulbs out of the soil. Typically, lilies are planted 4-8 inches below the soil's surface.
Remove excess dirt outside and then wash them gently in some water.
Use your hands to separate the bulbs. Separate even little ones. You should not use a knife to divide lily bulbs.
Plant the separated bulbs immediately while you can still dig into the ground. Keep in mind that lilies like well draining soil (add some compost if necessary) and that small bulbs may not bloom for several years so you may want to place them in a separate area of your garden.