Irises (Iris spp.), hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9, and gladiolus (Gladiolus spp.), hardy in USDA zones 6 through 10, are both in the iris family (Iridaceae) and share a number of similarities. However, when in flower or when planting initially, one can hardly be mistaken for the other. When blooms are not present, however, there might be some confusion in identifying growing plants, since their foliage is very similar.
Iris foliage is medium green and sword-like. The foliage fans out from the bottom and blades may be wide or thin, tall or short, or variegated in color, depending on the species or variety. Gladiolus foliage is nearly identical in shape and height, but sometimes the leaves appear more ridged, depending on variety or species. Although gladiolus plants do produce variegated leaves, they are very rare and few if any are in production.
What are collectively known as bulbs may include rhizomes, corms, tubers or true bulbs. Irises produce rhizomes, an underground stem that should not be planted too deeply. Rhizomes are long, thick and fleshy, similar in appearance to the ginger roots purchased in grocery stores. Foliage emerges from several growing points along the rhizome. Gladiolus, on the other hand, emerge from corms. Corms are rounded, somewhat flat underground storage organs that slightly resemble onions. Foliage emerges from the center of the corm.
The flowers of both the iris and the gladiolus are perhaps the most the most obvious factor of identification. Iris flowers have standards or upper petals, falls that are lower petals or sepals, crests or tiny petal-like structures in the center, and sometimes beards or furry section on the falls. Gladiolus also have six petals, but they all point outward. Iris flowers open one at a time from the top of the flower stalk down, while gladiolus flowers open many at a time on one side of the stalk and mature from the bottom of the stalk upward.
Care and Culture
Iris and gladiolus require about the same maintenance. Both need good drainage, but the iris is more sensitive to overly moist soils. Iris rhizomes need to be close to the soil surface, while gladiolus corms can be planted more deeply. Both need at least 6 hours of full sun, and both thrive at pH levels of about 6.5. Both get the subsequent year's energy in the current year's foliage, so both need to retain the current year's foliage as long as possible for healthy growth the following year. Both do not favor high nitrogen fertilizers, since nitrogen promotes foliage growth over flower production. For iris, high nitrogen fertilizers may also promote root rot. Gladiolus flower stalks may need staking more than iris flower stalks.