First time I've noticed seed pods on the Lilac tree. Guess I just haven't paid that much attention to them...
I assume you leave them alone until they naturally open, but do I need to let them winter and plant next year?
Lilacs (syringa) may have slightly different germination requirements depending on which one, but in general, most need to have the seeds exposed to a period of moist cold before they will germinate. Moist cold ( about 35-40F) of anywhere from 1 - 3 months, followed by additional 2 - 8 weeks at approx 70F for germination.
Seeds are surface sown, some light may be beneficial to germination.
Most lilacs we are growing are hybrids and/or grafted - propagating from seed may not produce plants similar to the parent. You could have something lovely, or something not worth the space in your garden :)
This is the Lilac.
I have a hillside that I'm letting grow back in.
Really like the way this one is growing and would be nice out there.
When I collect the pods, I'll take half in to do what you suggest.
The other half I'll sow on the hill and let nature take it's course.
This will be an interesting experiment!