When to Plant Gladiolas

Planting Times

• The general rule for planting gladiola corms is anytime from midwinter to spring when the soil has warmed and there is no longer threat of frosts and freezes. Near the Canadian border, planting occurs in May or early June, in the central United States in April and May, and in the southern U.S. where corms are hardy in the ground year round, anytime from February through April. In the deserts of the American Southwest, corms are planted from November to January, according to "Sunset Western Garden Book." This allows gladiolas to bloom before the onset of the extremely hot summer, when flower-disfiguring thrip insects are in greatest numbers.

Extending the Flowering Season

• Gladiola corms produce only one flower spike and once it wanes, no replacement spike or reblooming occurs. To extend the flowering season, gardeners plant corms in succession. After the threat of frost passes, corms are planted in one to two-week intervals over a six-week period. This results in plants in different developmental stages so when the oldest plants finish flowering, the second and third plantings are coming into flower.

Planting Corms

• For ease of root development and growth, gladiola corms need a crumbly, light-textured soil. A fertile, sandy loam is ideal, but adding compost or other organic matter to sand and heavy clay improves texture, fertility and drainage more conducive for gladiolas. If possible, avoid planting broad, flat-shaped corms as they are older and less vigorous, according to "Sunset Western Garden Book." Plant corms four times deeper than their height, positioning the tapering pointed side up to the sky in the hole. In heavier loam or clay soils, plant the corms more shallowly, such as two to three times deeper than the corm height. The general planting depth for gladiola corms is between 3 and 6 inches deep. Space corms 4 to 6 inches apart.

Follow-up Care

• Supplement natural rainfall as needed to maintain an evenly moist soil when leaves and flowers exist. Avoid both dry soils as well as soggy conditions, which encourages root and stem rot and gray mold. Staking isn't always necessary or recommended for gladiolas, unless they are in a wind-exposed garden location or the cultivar is exceptionally tall growing. With rain or wind downbursts from thunderstorms always a possibility, shallow-rooted plants and those planted in loose-textured sands may lean and topple more readily.