Although gladioluses are often referred to as bulbs, technically they are not. Glads grow from corms, which are chunks of underground stems that produce roots, stems and flowers from food stored in solid center tissue. Bulbs are similar in appearance, but store their nutrients in scales instead. When choosing the corms, big is not always better. The great, big, round flat ones may be 5 or 6 years old and probably past their prime.
Gladioluses do best in soil that's rich in organic material and drains well.
Although the plants like moist soil, beds that remain soggy may rot the corms. Glads also prefer full sunlight. But in hotter, inland areas, they will tolerate some early morning or afternoon shade. The average time from plant to bloom is about 85 to 90 days. Because most of their growth is straight up or straight down, glads can be planted as close together as 4 to 6 inches.