Both the white and the red ones have been seeding around for several years but the seedlings haven't reached flowering size yet. The flowering clumps get bigger each year too. I hope/expect someday that much of the backyard woodland beds will be carpeted with trilliums in the spring! I try to give the trilliums the same sort of conditions that exist in a nearby woodlot that has a fabulous display of trilliums each spring - I leave all the fallen leaves, do not give them supplemental water, and try not to disturb the soil around them. This patch also has a 'nurse' log:

Where I grew up, the red trilliums were most common so I have a nostalgic fondness for the red ones :-

The red ones here seed around but not as freely as the white ones as you can see by the fewer seedlings visible in this picture: