Gladiolus, often called the “sword lily,” is a vibrant summer-blooming flower grown from an underground storage structure known as a corm. Successfully growing gladiolus in Texas depends on planting precisely when the threat of cold weather has passed and the soil has warmed sufficiently for root development. Because the Texas climate spans multiple hardiness zones, a regional approach is required to determine the optimal planting window.
Regional Planting Timelines Across Texas
Planting time for gladiolus across Texas is determined by the last expected frost date and a soil temperature of at least 55°F (13°C). Planting corms in a series, roughly every two weeks, starting at the earliest possible date, ensures a continuous flowering period throughout the summer.
North Texas
In North Texas, including the Panhandle and the Dallas-Fort Worth area (USDA Zone 7 and 8a), planting should begin only after the last hard frost, typically in late March or early April. Staggered planting should continue until early summer to maintain blooms through late August.
Central Texas
Central Texas, covering areas like Austin and San Antonio (Zone 8b), has a milder climate allowing for an earlier start. Corms can be planted beginning in late February or early March, provided the soil has reached the minimum temperature threshold. This longer growing season allows for succession plantings, extending the bloom period into the hotter months.
South and Coastal Texas
In the South and Coastal Texas regions, such as Houston and the Rio Grande Valley (Zone 9 and 10a), the planting window opens the earliest, sometimes in January or February. However, extreme summer heat can be detrimental to bloom quality. Gardeners here often plant very early to maximize spring and early summer blooms or treat them as annuals.
Essential Site Preparation
Selecting the correct site is important for gladiolus success. Gladiolus requires a location that receives a minimum of six to eight hours of direct sunlight daily. While they can tolerate partial shade, insufficient light results in weak stems and sparse blooms.
Poorly drained soil is the most common cause of gladiolus failure, as corms are susceptible to rot. Texas soils, often heavy in clay, must be amended deeply—up to 12 to 15 inches—with organic material like compost to improve drainage and aeration. The ideal soil composition is a fertile, well-drained sandy loam with a pH that is slightly acidic to neutral.
Planting Techniques for Optimal Growth
Once the planting site is prepared, pay attention to depth and orientation. The corms should be planted with the pointed side facing upward. A planting depth of 4 to 6 inches is standard, though larger corms benefit from a deeper placement, up to 8 inches, to provide better stability for the tall flower stalks.
Corms should be spaced 4 to 6 inches apart to allow for adequate air circulation and growth. After placing the corms, cover them with soil and water thoroughly to settle the soil and initiate root growth.
Managing Corms After Bloom
Post-bloom care allows the corm to store energy for the following season. Once a flower spike has finished blooming, the spent stalk should be cut off, but the foliage must remain intact. The leaves continue to photosynthesize for approximately six weeks, transferring energy back down to the corm for the next year’s growth.
When the foliage naturally yellows and dies back, the corms are ready to be lifted, especially in cooler parts of Texas where winter wetness or a hard freeze poses a risk. After digging, the corms should be cleaned and allowed to cure in a warm, well-ventilated, dry area for two to three weeks.
Cured corms must then be stored in a cool, dark, and frost-free location, ideally between 40°F and 50°F, until the next spring planting. In the warmest parts of Texas (Zone 9 and 10), gardeners may leave corms in the ground with protective mulch, but lifting and storing offers the best guarantee against rotting during a prolonged, wet winter.