Digging Up Gladiola Corms: How To Store Gladiolus For The Winter
Image by StephanieFrey
& Anne Baley
In order to enjoy the beauty of gladiolus flowers year after year, most gardeners must store their gladiolus corms (sometimes also referred to as gladiolas bulbs) in the winter. Gladiolus bulbs, or corms, aren’t hardy through frozen winter months, so you must dig them up and store them until spring if you want to grow them again the next year. Read on to learn more about how to store gladiolas for the winter.
Digging Up Gladiolus
Many people make the mistake of digging up gladiolus corms too early by doing it before the foliage has died. For the proper gladiolus winter care, you should wait until the first frost has killed off the foliage above the ground. After a gladiolus flower spike is done blooming, the plant concentrates its energy into the corm at the base of the stem.
Digging up gladiolus can start about eight weeks after this, but you can do it any time until the frost arrives. Knowing when to dig up gladiolus corms might be the trickiest part, but it’s generally safe if you wait until all of the plant matter has turned brown and died back. Once the foliage is brown, you can start gently digging up the gladiolas corms from the soil.
Storing Gladiolus Bulbs
Dig the corms of gladiolus using a garden fork or spade, digging far enough away so that you don’t touch the corm. Pull the plant by its dried leaves and shake it gently to remove any loose dirt. You may see some miniature corms growing on the bottom, which you can grow into full-sized plants in a couple of years.
The next step in gladiolus winter care is to “cure” the gladiolus corms. Leave dug corms on top of the soil for two days to allow them to dry. Transfer the corms to a cardboard box and place it in a warm dry place with good air circulation, at about 85 F. (29 C.). Keep the corms here for about two weeks to allow them to dry completely.
Separate the parts of the corm after they are dry. Gladiolus forms a new corm on top of last year’s old one, and you’ll be able to separate the two after drying, as well as removing the cormlets. Discard the old corm, and place the new corms and cormlets back into cardboard boxes, after removing any excess dirt you may find. At this time, you can also cut the dead foliage off.
What to Do with Corms of Gladiolus Over Winter
When storing gladiolus bulbs, it’s important that you defend against rotting and diseased corms. Inspect them before final storage, throwing away any you find that have soft spots or mushy places. Dust the corms with an anti-fungal powder before putting them away for the winter.
When thinking how to store gladiolus over the winter, think about imitating the environment the corms would experience in nature, only just a little bit better. Place them in single layers in cardboard boxes with newspaper in between the layers, or store them on screens or in onion bags. You may also place the corms in a breathable bag, like a paper bag, a cloth bag or nylon pantyhose. This will allow the air to continue to circulate around the gladiolus corms while they are being stored.
Keep the corms in a cool, dry spot just about freezing, or around 40 degrees F. (4 C.). Many people choose the vegetable bin in their fridge or an attached garage to store their gladiolus corms. An unheated basement or enclosed porch is ideal as well. Store the corms until next spring, when all chance of frost has passed.
Now that you know how to store gladiolus for the winter, you can enjoy their beauty year after year.
Gladiolus is a flower of many names (Sword lily, Corn Lily, Xiphium), many colors (ranging from pure white to almost black) and multiple applications- they’re priceless at the back borders, great for cutting gardens, floral arrangements and bouquets. These strikingly showy plants, planted right, are a breeze to grow and sheer joy to behold. Here’s some intel on planting Gladiolus that you might find helpful.
When to plant
Spring is the best time for planting gladiolus bulbs. A majority of gladiolus varieties are hardy to zone 7 and as such, can be left out in the garden over the cold season. Those in colder places can plant gladiolus bulbs after the last frost date in spring.
Where to plant
Look for a site that gets full sun and isn’t subject to strong wind. Gladiolus isn’t too picky about the type of soil. It must, however, drain well. You’d do well to incorporate a 2-4 inch layer of compost into the planting beds to improve the soil’s fertility and drainage. Also, rid the planting site of all weeds and debris.
How to plant
Depending on their size, gladiolus bulbs should be planted 2-6 inches deep, the pointed end facing the skies. Space the bulbs about 5 inches apart in rows. You can also plant gladiolus in groups of 10-15, with 4-5 inches separating the adjacent plantings. Cover up with soil, level the ground and then water, enough to soak the soil. Taller varieties of gladiolus require staking at the time of planting. Take care not to damage the bulbs in the act. Provide a 2-4 inch layer of mulch around the bulbs. This will aid moisture retention and help suppress weed growth. Make sure you irrigate periodically if the rainfall is less than an inch a week in summer.
Gladiolus flowers will be out and in bloom within 70-90 days of planting, coloring your space beautiful right till the first frost.
Shop All Gladiolus
Maybe you won’t have to bring your gladiolus corms back indoors for the winter! Source: westcoastseeds.com
Most gardeners in cold regions (hardiness zones 7 and below), even beginners, know you’re supposed to dig up gladiolus (Gladiolus x hortulanus) corms in the fall. You then roughly clean off the corms (bulbs), cut off the leaves and store them cool and dry for the winter. (Read Soon Time to Bring Tender Bulbs Indoors for more details on this technique.)
That’s pretty classic information and generations of gardeners have done just that with their gladiolus. No one will deny that it’s simply the best way to keep them alive and well. Even so, if you leave them in the ground, it just might happen that your gladioli survive the winter to bloom again. They can even persist that way for many years.
Most gardeners who discover this phenomenon do so by accident. They forgot to bring in their corms or just didn’t have time. Either that or they decided all that digging and replanting just wasn’t worth the effort. For whatever reason, they left their glads out for the winter and the following summer, most grew back and flowered, just like before.
The accepted hardiness zone for the classic Grandiflora gladioli (your typical garden glad) is zone 8, but it’s well known that by covering them with a good mulch, you can keep them alive in zones 6 and 7. But what’s more surprising is that sometimes (and there is no guarantee!), they survive the winter zones 4 and 5, even zone 3 with only the slightest bit of protection.
Planting the corms deeper than usual and in well-drained soil can help perennialize them. Source: gardenwise.co
Before thinking of leaving gladiolus corms in the ground over winter, it would be wise to reunite the best possible growing conditions, including:
- a location in full sun;
- loose, sandy or well-drained soil;
- extra deep planting (6 inches/15 cm rather than the usually recommended 2 to 4 inches/5 to 10 cm);
- 6 to 8 inches (15 to 20 cm) of well-aerated fall mulch;
- a good layer of snow.
Under those conditions, I find that I can grow glads outdoors with reasonable success (I do lose a few and their numbers slowly decrease over the years) in my USDA zone 3 (AgCan zone 4) garden … and that’s really cold!
Some Varieties Are Hardier Than Others
Dwarf gladioli are hardier than standard gladioli. Source: jparkers.co.uk
Of course, some varieties are hardier than others. To start with, dwarf gladioli (often sold under the name Gladiolus nanus, although in fact there is no such species) are well known to be hardier than the usual Grandiflora hybrids and can be safely grown in zone 6 without protection. With a good mulch, they’re pretty much certain to thrive in zones 4 and 5. Among other gladiolus cultivars known for extra hardiness are ‘Boone’ and ‘Carolina Primrose’.
Gladiolus communis byzantinus is a naturally hardy species of gladiolus. Source: ;Meneerke bloem, Wikimedia Commons
Then there are also species gladioli that are naturally very hardy. Originating in Europe and Asia (hybrid varieties are mostly derived from South African species), some grow in regions with very cold winters indeed, such as on the Russian steppes. Authorities usually say they’re hardy to zone 6, but I suspect that some at least are much hardier than that. These glads are proving hardy in many zone 4 gardens … and that’s with no special protection. In this group are Byzantine gladiolus (G. communis byzantinus, syn. G. byzantinum) and Turkish marsh gladiolus (G. imbricatus), both modestly available by mail order if you know where to look.
I’ve been growing Byzantine gladioli in my garden (again, USDA zone 3/AgCan zone 4) with no special attention for almost 20 years, although they do profit from good snow cover. They’re actually proving a bit weedy and I have to pull out excess ones when they start to spread too widely.
Note that these Eurasian gladiolas need to be treated like hardy bulbs and planted in the fall, not in the spring like tender glads. In other words, you have to treat them like tulip or narcissus bulbs. They flower around at the same time as the tulips too, well before the classic gladioli. Spring-planted corms (and some shady suppliers do sell them in spring) will not adapt well: they need a cold winter in order to thrive.
Gladiolus murielae is less hardy than standard gladioli. Source: Jitka.karlikov, Wikimedia Commons
On the opposite end of the spectrum, some gladioli are less hardy than Grandiflora glads. The popular Acidanthera or Abyssinian gladiolus (G. murielae, formerly Acidanthera murielae) won’t tolerate much colder than zone 8, perhaps zone 7 with good winter protection. Then there are out-and-out tropical species, too, like Gladiolus pole-evansii, rarely grow beyond zone 9.
Should You Take the Risk?
There will always be a risk when you plant anything beyond its accepted hardiness zone. I therefore suggest you bring indoors in the fall any gladioli that are of great value to you. However, if you have extra plants you could live without, experimenting by pushing gladiolus hardiness limits could definitely be worthwhile.
I’m not sure what you mean by “dangerous” – i.e., dangerous to squirrels and other animals, or to small children who are naturally curious and put everything in their mouths? Take a look at a previous entry on our website, “Will our squirrels eat gladiolus buds?”, which highlights that the little critters love to eat the bulbs (as well as buds and flowers).
Of note, gladiolus bulbs (called corms) can cause symptoms that include nausea, vomiting and skin irritation, according to the University of Wisconsin Health Wisconsin Poison Center’s “Common plants – what’s poisonous and what’s not?”. This publication also includes lots of non-toxic plants.
PennState Extension’s “Spring plants that are poisonous to horses, dogs and barn cats” states that gladiolus corms can cause salivation, vomiting, drooling, lethargy and diarrhea in cats and dogs, if ingested.
If by “dangerous” you mean”, risks the winter killing the plant”, gladiolus corms should not be left in the ground year-round, as most varieties are hardy in zones 8a-11. They are usually planted in mid-May through mid-June, so that flowers will bloom through July & August. Once the foliage has been killed off by frost, the corms should be dug up and stored.
If you wish, leave a few corms in the ground over winter as an experiment, chances are they will rot in the cold soil, but some growers indicate that glads can over-winter in the ground, even to zone 5. However, this would not be predictable, so you could be gambling each year that the corms would survive the winter. That being said, mulching the glads could protect them from the winter weather, and if your properties are blanketed with a good (insulating) snow cover, the corms would have a better chance of surviving. The Gladiolus nanus ‘Atom’ is hardy in zones 6-10 (needs thick mulch covering where winters are extreme). It grows to around half the height of the glads most of us are used to.
If you decide against glads, see “Long blooming perennials: a Toronto master gardeners guide “. I have found Geranium ‘Rozanne’ to be super-easy to maintain, while blooming over several months.
See also the Missouri Botanical Garden’s “Perennials for season-long bloom“, which may give you some ideas.