I don't grow many lilies but I do grow a lot of daylilies and I use a slow release fertilizer like Osmocote but a less expensive version. Scotts has a vegetable and flower slow release that I get at Lowes for a reasonable price. Usually I use a formula as close to 10-10-10 as possible. Daylilies also like minimum of 1" of water weekly and should be planted in full sun. Keep in mind though that there are some cultivars that will always have smaller fans than others. A lot of spider/ufo types are like that and its just in their genetics.
