The right planting time for gladiolus bulbs is once the soil starts to warm after the last frost in the spring. Planting the bulbs too early increases the risk of a late frost killing them.
To plant gladiolus bulbs, till the soil of the planting site that has access to full sun to a depth of at least 12 inches, and work in 4 inches of compost to improve drainage and enrich the soil. Dig a 4-inch deep hole, and place the root end of the bulb in the hole with the pointed end facing upward. Place the holes at least 3 inches apart to give the plants room to grow. Cover the holes with soil, and tamp it down.
After planting the bulbs, layer up to 4 inches of mulch over the soil to help it retain water. The mulch plus rain water, as long as 1 inch falls per week, is sufficient moisture for the plants. If not enough rain falls, water the plants so that the soil remains moist. Once the flowers begin to fade, snip them off. After all the flowers on a single limb have bloomed, cut the stalk off. Winterize the plants by placing several inches of straw over the bulbs. However, remove the bulbs if you live in an area with frosts.