Originally posted by: Bryophyte
Don't worry about them too much. If you're going to be laying sod there, they won't be able to survive the frequent mowings.
Exactly.
They spread like crazy. Have you noticed them encroaching on the yard? No?? That's because when you mow the yard, you're cutting off the green part of the tiger lily, which supplies energy for the bulb, which eventually withers up and dies.
Just hoe up the area that needs grass, plant grass seed. As the tiger lilies start to grow back, mow them down along with the grass. The grass survives being cut low. Tiger lilies won't for very long.