I had the same question 2 years ago, and there were so many I thought "what the heck," and sowed them in the fall. I now have lots of blackberry lilies, all from those seeds. Blooming now up here in northern Wisconsin, since first week of August. Just tossed them on the ground. I don't think they are even for my zone. Some bloomed the first year.

Hey,

Yup, you can basically just throw them in areas, you would like them to grow and your sure to get seedlings coming up in Spring!! You can also try wintersowing them!! They do require a cold period so it's best to plant now or winter-sow!
:)
~heavenlyfarm

P.S. I have had much better luck just letting them do their thing and throwing the seeds around in Fall!

And for opinion #3... I put dry seeds (that I was given) in the fridge over winter and planted them in the spring of 2014. Germination was erratic and slow. But many germinated and grew. I had no flowers the the first year but expect many next year. These are my very first blackberry lily plants (no previous experience).

Sounds like fall / winter / spring sowing works. The common theme seems to be a cold period.