When should I plant gladiolus bulbs outdoors?
Gladiolus bulbs (corms) should be planted after the danger of frost is past. In Iowa, it’s generally safe to begin planting gladioli in early to mid-May. Make successive plantings every 2 weeks for continuous bloom from mid-summer to early fall. Gladiolus corms bloom approximately 8 to 10 weeks after planting. The final planting should be made in early July.
When purchasing gladioli, select corms that are 1½ to 2 inches in diameter. Smaller corms will not bloom as well. Plant the corms 4 to 6 inches deep. Gladioli perform best in well-drained soils in full sun. Planting sites should receive at least 6 hours of direct sun per day.