Gladiolus' tall graceful spikes come in a huge array of flower colors and are long-time garden favorites. But before the flowers are in bloom and after the blooms have faded, the plants themselves are not particularly attractive. The sword-like foliage is unremarkable, and the plants can make an otherwise beautiful garden bed look rather messy and unkempt.
Many gardeners learn to plant gladiolus among other flowers, or to hide a group planting behind lower-growing plants to disguise the glads until the spectacular bloom period. But another solution is to plant gladiolus in containers, where you can place the growing plants wherever you want until they bloom and are ready for you to harvest for cut arrangements. Once cut, either treat them as an annual flower and discard the stems and corms, or let the foliage fade, then dig up and save the corms for replanting next year.
Here are some tips for growing gladiolus (also called gladiolas or just glads) in pots.
When to Plant
The rule of thumb for gladiolus is to plant them at the same time you would plant sweet corn in your area—assuming you are planting in the ground. If you are not a vegetable gardener, this means that garden gladiolas should be planted about 2 weeks before the last spring frost. Gladiolas require 70 to 90 days to flower, which means that corms planted at the beginning of May will flower in mid- to late-summer. Gladiola enthusiasts often stagger plantings every 2 weeks to ensure a supply of flowers for cutting throughout the summer and early fall.
When planting in pots, you can plant even sooner, because the soil in pots warms up much faster than the soil in the ground. You can plant up to 4 weeks before last expected spring frost, provided you are willing to protect the plants on those nights when frost is expected.
How to Pot Glads
Gladiolus are fairly forgiving and corms purchased from reputable nurseries and garden centers are usually hearty and easy to grow. They do have some important requirements, however, in order to thrive in your garden.
- Choose a pot tall enough to support them: Glads grow to be very tall—some reach 3 to 4 feet in height, but the root systems are not very robust. Although the planting depth is only about 3 to 5 inches, you will need to drive deep plant stakes to help support the stalks. Glads planted in short, squat pots will grow, but without the support of long stakes, they can easily blow over. One option is a reusable canvas grocery bag that has the depth (and girth) to easily grow several glads. Most experts say that a pot needs to be at least 12 inches deep and wide to accommodate gladiolas. And there will need to be at least 2 to 4 inches of soil below the corms.
- Provide good drainage: Make sure your pot has good drainage—if the soil remains wet, the corms will rot. Make sure the pot has one large hole or several small holes so excess water can drain out. Some gardeners place 1 to 2 inches of gravel in the bottom of the container, covered with a layer of landscape fabric to prevent the soil from draining down and clogging the drainage holes.
- Use good potting soil: Glads like fast-draining soil so their roots don't sit in water, so be sure to choose high-quality, loamy potting soil. Also, if your potting soil doesn't include slow-release fertilizer, add this before you plant. Use organic, all-purpose fertilizer and mix it into the soil once it is in the pot. Be sure to follow application directions, particularly for conventional fertilizers, as you don't want to over-fertilize.
- Plant the corms 3 to 5 inches deep, with the root side down: The corms will usually have one or more "eyes" on top, sometimes found under a papery corm tissue; these are the future plant stalks, so this is the side that should face up. For a long display, plant a new pot every two weeks—however, be aware of the first frost date in the fall for your area. Glads take 70 to 90 days to grow and bloom, so if you have short summers, you may be able to get in only one or two plantings.
- Position the pot in full sun: Gladiolas are sun lovers. They prefer full, unobstructed sun for most of the day, but they will still grow provided they get at least six hours of sun in the middle of the day. One of the advantages of planting in pots is that you can move them around as sun patterns change to ensure they get plenty of sunlight.
Caring for Glads
Potted gladiolas are fairly easy to care for if you follow some simple tips:
- Stake and support: These tall, skinny flowers may flop over unless you stake them. Once the plant stalks are about 6 inches high, pack soil around their base to improve stability. You can also stake the stalks individually or create a corral by using bamboo stakes with string or twine.
- Water heavily once a week: A single soaking once a week is much better than light waterings several times a week. After you can cut the flowers, continue to water the foliage and corms until the leaves begin to dry up and turn brown.
- Fertilize when you plant, then no more: Potted glads should be fed with a slow-release fertilizer when you plant, but not after that. No fertilizer is necessary if the potting soil you use has plant food already mixed in.
- Cut them early: Gladiolas are ready to cut as soon as the lowest buds on the stalk start to show color. Cut the stems on an angled bias and quickly put the flowers in water. For long-lasting blooms, change the water in your vase daily.
- Leave the foliage in place: After cutting, the corms will replenish themselves if you allow the foliage to remain in place until it turns brown and dries up. If you plan to discard the corms, you can remove and dispose of the foliage and stalks immediately.
How to Overwinter Corms
For zones 7 and 8, you may be able to overwinter your gladiolas right in the pot by mulching them with hay or straw. You can also try putting the whole container in a dark, cool indoor space for the winter.
In colder climates, you can try to overwinter gladiolas by digging up the corms before the ground freezes—roughly 8 weeks after blooming. Clean off the soil, either by washing or brushing and cut off the stalk as close to the corm as possible. Gladiolas normally form new corms on top of the old corms; you will be discarding the shell of the old corm and saving the fresh, new corm. There may also be small offshoot corms—"baby" corms, or cormlets—attached to the main corm. These can also be saved and replanted, though it may take several years before they are mature enough to produce flowering plants.
Ensure that the corms are completely dry before storing them in mesh bags, open paper bags, or boxes for the winter. Store them in a dry, well-ventilated, cool area that doesn't freeze. According to the North American Gladiolus Council:
"A well-ventilated root cellar is ideal but any room with good air circulation in the average home basement will suffice if temperatures can be kept between 38 - 58 degrees. The lower temperature is the best."