Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
If you are starting a cutting garden, gladioli are a must. They are a classic flower for arrangements. They also work well as a background plant in your border.
What is Gladiolus?
Gladiolus (Gladiolus spp.) is a genus of flowering plants that are related to iris. They are native to Asia, tropical Africa and Southern Europe. They are only hardy through zone 8. They can survive winter in zone 7 if they are heavily mulched. In colder climates, gladioli are grown as annuals. The corms are lifted from the soil in the fall and stored indoors during the winter.
Gladioli grow from corms similar to crocus. Corms are different from bulbs. Both are underground stems that store food to help the plant survive the winter or other extreme weather conditions like drought. In bulbs, the food is stored in scales that are actually leaves. Corms, on the other hand, store food in the stem itself. The surrounding leaves protect the stem from insects, animals or drought.
Gladioli have narrow sword like leaves, hence the nickname sword lilies, like their iris cousins. The leaves all grow from single stem. The plants do not branch.
The flowers grow on tall stalks like iris but look more like lily flowers to me. All the flowers bloom on one side of the flower stalk. They have been bred to come in every color except blue. Gladioli can grow to 5 feet tall and need to be staked for support.
Because of their height, gladioli make great back of the border plants. They are also effective when planted in groups. Group plantings are also good so that the plants can support each other rather than being individually staked. Aim for groups of at least 7 for the biggest impact.
How to Grow Gladiolus
Gladioli grow and bloom best in full sun. They will grow and flower in partial shade, but they won’t grow as well and the flowers will not be as brilliantly colored. They require well-drained soil. The corms will rot in heavy clay soils that don’t drain well.
Keep them moist, at least 1 inch of water each week. A thick layer of mulch (2 – 3 inches) will help keep the soil moist between waterings as well as prevent weeds from growing that will compete with your plants for sunlight, water and nutrients.
Mix some compost into your soil before you plant your gladioli. If you prefer to use commercial fertilizer, use a balanced fertilizer such as 10-10-10. You can fertilize when the plants are about 10 inches tall and then again when the buds develop to give your plants a boost.
Gladioli flowers open a few at a time from the bottom of the stalk to the top. Remove the flowers as they die to ensure that your plants will continue blooming all the way to the top of the stalks. When all of the flowers have opened and then been removed, remove the flower stalk by cutting it 2 – 3 inches from the top of the soil.
Leave the foliage to continue to grow until the fall. The leaves are making food for the corm so that it can grow and bloom next year.
How to Plant Gladiolus
Resist the temptation to plant your corms until after your last frost when the soil has warmed to 55⁰F. The corms will not germinate in cold soil. Once the soil has warmed, plant your corms 4 inches deep with the pointed end facing upwards. The flat side is where the roots will grow so it should be facing down. Space your corms 6 – 8 inches apart. This is a good time for you to add your stakes. If you wait until after the plants start to grow to install your stakes, you risk damaging the roots.
It will take 60 to 90 days depending on the variety for your plants to grow and bloom. Rather than planting all of your corms at once, try planting a few every 10 days. This will ensure that you have continuous flowers through the fall.
How to Harvest Gladiolus for Use as Cut Flowers
There are just a few extra steps necessary to successfully harvest your gladioli flowers to use in your flower arrangements. Always harvest them in the cool of the early morning or late evening. The heat of the day is very stressful for plants. The flowers will look their best and last longest if you cut them when the weather is cooler.
In addition to your pruners or a sharp knife, bring a bucket of lukewarm water out to your garden. Choose flower stalks that only have 1 or 2 flowers open. The rest will open after they are harvested. Cut the flower stalks on the diagonal and immediately plunge them into the bucket of water. Cutting on the diagonal maximizes the area of stem that can take up the water to keep the flowers fresh.
Bring your bucket of flowers indoors and place it somewhere cool and dark for a few hours to allow your flowers to rest and get acclimated to being indoors. Once they are acclimated, you can use them in your arrangement. The unopened flowers will start to open indoors just as they would outdoors. Be sure to remove the lower flowers as they die to encourage the rest to open. Every few days, you should “freshen” the cut on the stems by cutting another inch off of them, again on the diagonal.
How to Store Gladiolus Corms Indoors During the Winter
If you live north of zone 7 you will need to dig up your corms in the fall and store them during the winter.
In the fall when the foliage is fading but before it is killed by a frost, carefully dig up the entire plant. Shake off as much soil as you can and cut the plant off about 1 inch above the corms. The one corm that you planted last spring will have multiplied. There will be several smaller corms around the top. You can either discard them or you can save them also to replant in the spring. They will not bloom for 2 or 3 years until they have grown large enough to support foliage and flowers. The first two years, they will only produce foliage. The foliage will make the food to help the corms grow.
You will need to cure your corms for 2 weeks after your dig them up. Curing is the process whereby the corms dry out on the surface so that they don’t rot while being stored. Cure them someplace dark, warm and airy. Be careful while handling them not to damage the brown husk surrounding the corm. This is protecting it. Once the corms are dry, you can store them in your (cool) basement in paper or cloth bags.
© 2020 Caren White
Caren White (author) on June 01, 2020:
So happy to hear that you will be adding these stunning flowers to your garden.
Linda Crampton from British Columbia, Canada on May 31, 2020:
Thank you for sharing these instructions. My parents grew gladioli in our garden when I was a child. I loved the flowers. Your article has encouraged me to grow them myself.