Lilium michiganense, Lilium canadense (plus few others) are the kind of lilies that require warmth for the first stage of germination (about 20˚C), and then a period of cold (0-5˚C for 2-3 months) for the true leaves to emerge. If you get these seeds in late fall or winter, this is the tried recipe to make sure that they’ll start growing leaves in the spring:
Place the seeds in a Ziploc bag with moist vermiculite and keep them during the winter months (Nov/Dec.-Feb/March) at room temperature. Check the moisture once in a while. After the tiny bulblets appear, place the Ziplocs in the fridge for the cold treatment (March-May). Pot them afterwards and place outside.
These bulblets had their photos taken and now are ready to switch places in the fridge with the seeds that are coming out for sowing. Some grow out of the seed and are visible, while some can remain more or less enclosed.
And bulblets of another woodland edge growing, tall Lilium (supposedly canadense); we didn’t catch it in flower last year, but it was an impressive exemplar. It has been placed on the ‘watch list’ for this year so we can properly identify it.
Although North American native species, these Liliums and also few others are almost never grown by commercial nurseries. Start growing your own, besides being ‘hot’ plants, they are pollinated by hummingbirds, sphinx moths and butterflies like the Monarch and Spicebush Swallowtail!