For an established clump of true lilies, autumn after the foliage has naturally yellowed is usually a convenient time to lift and transplant the bulbs. Work while the soil is workable, and account for local weather. There is no single September or October date that fits every garden.
Make sure these are true lilies
This advice is for Lilium, including many Asiatic and Oriental lilies. Daylilies are Hemerocallis and have a different root structure; calla lilies and other plants with “lily” in their names also need different guidance. For daylilies, use the daylily transplanting guide.
Let the foliage finish its work
Do not cut healthy green stems off simply because flowering has finished. Retaining foliage allows the bulb to rebuild reserves. Mark the clump’s location before stems disappear so you can find it without digging blindly.
The University of Washington’s Miller Library discussion identifies fall as the usual recommendation while acknowledging that lilies can be moved at other times with care. An urgent relocation is different from routine dormant-season division.
If you must move an actively growing plant, preserve the root ball and shoots as far as possible and provide aftercare. Do not interpret the ability to move it as a guarantee that it will flower normally that season.
Prepare the destination before lifting
Choose conditions suited to the species or hybrid, especially good drainage. A chronically waterlogged planting hole is not corrected by a little compost placed over the top. Plan enough room for the mature stems and access for watering or staking where needed.
Have the planting area ready before digging. Lily bulbs should not be left exposed to dry while other work is completed. Keep cultivar labels with the bulbs if several varieties are being divided.
Lift carefully and replant promptly
Begin digging outside the clump and loosen soil carefully, allowing for bulbs and roots deeper than the visible stems suggest. Lift rather than pulling hard on the stalks. Separate readily detachable offsets without unnecessarily breaking healthy bulbs or roots.
Remove dead stems when appropriate, but do not cut off live growth to “redirect energy” as a general transplanting rule. Keep lifted bulbs protected from sun and drying wind and replant promptly.
Planting depth depends on the type of lily and bulb size. The RHS lily growing guide distinguishes stem-rooting lilies and shallower-planted exceptions. Follow guidance for the identified lily instead of covering every bulb and small offset with the same fixed depth of soil.
Water, watch and divide only when useful
Water after planting to settle the soil, then monitor moisture without keeping the bulbs saturated. Adjust any mulch to the plant, climate and drainage; do not pile material against emerging shoots. Label the site so future digging does not damage the bulbs.
Small offsets may need time to reach flowering size. An immediate display is not a reliable test of whether the move succeeded. Divide when a clump is crowded or relocation is needed, rather than lifting every lily automatically every two or three years.
If growth declines after the move, check drainage, planting depth, root damage and the identity of the plant before adding fertilizer. These problems are not solved by feeding on a fixed schedule.
A serious risk for cats
According to the FDA’s lily safety guidance, true lilies and daylilies can cause life-threatening kidney injury in cats. Keep bulbs, foliage, flowers and pollen away from them. Suspected exposure needs immediate veterinary advice, even if the cat seems well.
