Gladiolus make a colorful addition to the garden and will naturalize in USDA horticultural zones 8-11. In colder areas the corms, or bulbs, will need to be dug up and stored over the winter in a warm, dry location. Corms are sold by size. Number one or number two sized corms cost more but provide larger and taller flowers.
How to Plant Gladiola Bulbs
Locate an area of the garden that gets at least 6 hours of sun daily, drains well, and is protected from strong winds. Gladiolas prefer sandy soil or sandy loam. If planting in heavy clay, lighten soil by mixing in compost. Gladiolas can reach 36 inches in height so plant behind shorter plants. Also, gladiola foliage must remain on the plants until it completely dies back for the bulbs to reproduce and will become unsightly before it can be removed.
Dig a trench, or planting area, 8 inches deep.
Add one cup of organic granulated fertilizer to bottom of trench for every 2 feet of row or for every 4 bulbs.
Add 4 inches of soil over the fertilizer application.
Place bulbs in soil 4 to 6 inches apart with the flat side down. Cover with 4 inches of soil, watering in well.