Plant lilies when the bulbs are available. Large retailers and many bulb suppliers will offer them in both the fall and spring. Bulbs are harvested in the fall - often the late fall - and are kept in cold storage until spring sales. Depending on the source, I prefer spring planting as those bulbs have not been held as long as those available for planting in September - September is generally too early for much of the harvest and so fall-available bulbs may have very well been held in limbo for many months. And fwiw, fresher bulbs will often produce better results.

Thanks so much! I have my heart set on the Candida and Stargazers for two clumps among the roses. :)