Soil. Gladiolus thrive in rich, well-drained, sandy loam soil. If the soil is too heavy and wet, the corms will rot. Light: These plants prefer full sun when growing and blooming. Gladiolus corms can also flower in the shade, but the colors are not as vivid as when grown under full sun. Also, if grown under the shade, the plant won’t grow quite as well.Spacing: Space the gladiolus corms at least 6 to 10 inches apart in the garden.Planting: Plant your gladiolus corms in spring, 2 weeks before the last expected frost date.