Pennisetum alopecuroides Fountain Grass Size: 2 to 3' high and 24 to 30" wide. Hardiness: Zones 6 to 10. Heat Zones: 9 to 1. Habit: Arching stalks of bristly, bottlebrush-like flower spikes that appear in late summer. The spikes erupt from the dense, upright mounds of slender, arching bright green leaves. Culture: Full Sun.