30 gladiolus bulbs in mixed colors fill your garden with glorious color. These are perfect for planting behind shorter flowers.These hardy gladiolus flowers bloom from midi-summer to frost in most areas. Gladiolus are annuals that like sunny, well-drained soil in zones 2 - 10. They are hardy in zones 8 - 10. Your gladiolus tubers will arrive at your home at the proper time for planting in your zone. Although gladiolus are supposed to thrive in zones 2 - 10, you might want to shelter them in lower zones.