To answer this question we tagged individual lilies in a defined plot at several locations near Saskatoon and began to follow their growth form and ability to produce seed from year to year. The availability of moisture at critical times is one important factor.
Lilies produce the shoot for next year in late summer, early fall.
If there is insufficient moisture in the spring the flower bud will not continue to grow and only the vegetative stalk remains. Research plots were established at the north end of Last Mountain Lake where the Canadian Wildlife Service uses management practices such as prescribed burning and pulse grazing to maintain the health of native prairie. Spring fires have a positive effect on flowering and seed set. Fire removes the prairie thatch or vegetative cover. The small mammals such as meadow voles and pocket gophers that eat the plant or harvest the bulb are temporally deterred.