You can dig and divide any time the number of plants has increased, and/or when they are getting crowded and/or when bloom quality declines. The best time to divide is when the foliage has died down, or early in spring before they sprout. You can actually transplant lilies any time, if you are careful, but it's easier on them when they don't have a lot of foliage to support. Lily bulbs never go completely dormant, nor do they grow new basal roots every year like tulips and narcissus, so do your best to keep all the roots on the bottom of the bulb intact for replanting. Don't tear the roots off the bulb. Spread the roots out in the hole when you replant. Don't bother trying to keep stem roots. They are temporary, as the stem dies down every year. However, if you're transplanting when the foliage is still green and healthy, yes, keep those stem roots! Roots that are attached to stem bulbs are different; if you plan to separate and replant the baby bulbs that grow on the stem, try to preserve the roots that are attached to those bulbs.

Jeanne

thanks... I'll try after they bloomed