I absolutely love filling my garden with bold, exotic flowers—but I’ve learned over the years that some of the most beautiful summer bloomers need a bit of a head start to really thrive. That’s why I always begin pre-sprouting my dahlias, calla lilies, and other tuberous plants indoors in early spring. If you’re curious about how to get the best out of these (sub)tropical beauties, I’ll walk you through exactly how I do it—and why it’s worth the effort.
Summer Bloomers: Pre-Sprouting Bulbs and Tubers
Dahlias, calla lilies, and the like are popular among ornamental gardeners for their magnificent flowers. To encourage summer-flowering bulbs and tuberous plants to bloom earlier, it’s worth starting them indoors as early as March. Here’s what you need to keep in mind.
Gardeners looking to fill their garden with particularly striking and exotic plants will find it hard to pass up summer-flowering bulbs and tubers like dahlias (Dahlia), calla lilies (Zantedeschia), or Indian shot (Canna indica). However, because these plants originate from (sub)tropical climates, they often struggle to get started in the cooler Central European spring. Some species—such as Canna or butterfly ginger (Hedychium gardnerianum)—wouldn’t bloom until autumn without early indoor forcing. Even for dahlias and gladioli, pre-sprouting can bring their bloom forward by a few weeks and extend the flowering season.
How to Pre-Sprout Bulbs and Tubers Correctly
First, inspect the bulbs and tubers. Whether freshly bought or overwintered from the previous year, if they appear dried out or shriveled, soak them in water for a few hours to rehydrate them. Then plant them in pots. Start by adding a drainage layer of sand, expanded clay, or gravel, as many (sub)tropical plants are sensitive to waterlogging. Add a layer of potting soil, place the bulbs or tubers on top, and then cover them with more soil so they are about five centimeters deep.
Success now depends on placing them in a warm and very bright location. If the plants don’t receive enough light, they will grow tall and spindly—a process known as etiolation—and their thin stems can easily bend or break under the weight of their blooms. A greenhouse is an ideal location. Water sparingly until the first shoots appear. Once growth starts, you can move them to a slightly cooler spot to encourage more compact growth. From mid-May onward—when nighttime temperatures consistently stay above 10°C (50°F)—you can transplant them to their final spot in the garden.
The Advantages of Pre-Sprouting at a Glance
- You can discard dried-out or dead bulbs and tubers before planting, helping avoid empty patches in your flowerbeds.
- Summer-flowering bulb and tuber plants begin blooming several weeks earlier and may flower for a longer period.
- Plants are already established and more robust by the time they’re planted outdoors after the last frost.
Especially Beautiful (Sub)Tropical Bulb and Tuber Plants
While the calla lily (Zantedeschia) is probably the most well-known in this group, there are many other stunning flowering plants that can thrive in our gardens with a bit of care:
- Butterfly Ginger (Hedychium gardnerianum)
- Glory Lily (Gloriosa superba)
- Pineapple Lily (Eucomis bicolor)
- Peruvian Daffodil (Hymenocallis festalis)
- Indian Shot (Canna indica)
- Tiger Flower (Tigridia pavonia)
For me, taking the time to pre-sprout my summer-flowering bulbs and tubers has made a huge difference in how vibrant and full my garden looks each year. It’s a simple step that leads to earlier and longer blooms—and it gives me a chance to connect with my plants even before the outdoor growing season begins. I hope this guide inspires you to give it a try and enjoy the same burst of color and life in your garden this summer.
