The tall ones spread more (5-7 feet) than the short ones (2-3 feet). If I didn't want them to spread, I'd do some cutting. In general with Alstroemerias, when the blooms are spent and the stalks start withering away, you have to pull the stalks out of the ground. The roots stay behind and start spreading. If you cut the stalks at ground level, the plants won't rebloom or spread. If I wanted the plants to stay within a small circle, I'd pull the stalks in that circle and cut the stalks outside the circle.
