As I look around my yard, the most brilliant blooms I see are the gladiolus. Often referred to simply as “glads”, these spikes of colorful flowers have delicate orchid-like blossoms. I love the way they add elegance to the flowerbed. And on occasion, when their heavy flower heads are too much for their delicate stems, I find the broken stalks also make spectacular cut flowers inside my home.
Growing Gladiolus Flowers
While these are wonderful reasons for growing gladiolus, I include them in my landscape design because they remind me of my mother. Her “secret” for growing gladiolus was to plant them by the dryer vent. She claimed the heat from the dryer warmed the soil which allowed the gladiolus corms to survive the winter in the ground.
On the surface, this seemed logical. I also planted my gladiolus bulbs near the dryer vent. Not only have my gladiolus corms survived our USDA zone 6 winters, but they have also propagated nicely. Where I planted a scant dozen corms, I now have dozens of gladiolus plants.
Yet over time, I questioned whether my mother’s rationale made sense. After all, she only ran the dryer on laundry day. Would heating the area once per week in the dead of winter prevent the corms from freezing? I think not. So why can I leave gladiolus bulbs in the ground over the winter? After all, classic gardening protocol states gladiolus is only winter hardy in zones 8 and warmer.
Why Can I Leave Gladiolus Bulbs in the Ground?
I love a good gardening mystery, so naturally I delved into why my gladiolus corms would survive the winter in the ground. Most of the articles I researched recommended digging and storing the bulbs indoors when growing gladiolus in zones 7 and colder.
It took a bit more research, but I ran across a reference for a type of hardy gladiolus (Gladiolus nanus). Unlike other types of gladiolus corms, these are winter hardy in USDA zones 5 to 7. Hardy gladiolus are available in a range of reddish-pink flower colors, and the most notable difference is they mature around 20 inches (50 cm.) tall, while other types can reach up to 5 feet (1.5 m.). My glads fit the height requirements, so I thought I’d solved the mystery.
Could I have planted hardy gladiolus? No, my glads more closely resemble the Grandiflora hybrids than the flowers on hardy gladiolus. I also found there are types of gladiolus which originated in Europe and these tend to be hardier than those native to Africa. Could crossbreeding produce hybrids which are more cold-tolerant?
Cold Tolerant Glads
Then I ran across posts from other gardeners relaying the same experience. Their gladiolus corms were surviving zones 5, 6 and 7 winters in the ground. Everything from global warming to a thick layer of mulch was credited for this phenomenon.
Perhaps my mother’s theory wasn’t so far-fetched. Was it possible the dryer vent created a microclimate suitable for overwintering gladiolus bulbs? And then again, maybe gardeners have been underestimating the hardiness of gladiolus for years.
Whatever the reason, one thing is certain. If you’re a northern gardener wondering, “Can I leave gladiolus bulbs in the ground overwinter?” The answer might be yes!