Time to Wake Up Your Tuberous Begonias

By Larry Hodgson

The tuberous begonia (Begonia × tuberhybrida) is among the most popular summer bulbs. Its ability to produce beautiful, large, colorful flowers all summer long makes it a star. And it can do this even in fairly shady spots where so few other plants bloom well.

But to have it in bloom from the start of summer, you have to start this begonia indoors several weeks in advance. Usually at least 6–8 weeks before the last frost date. That can be as early as January or as late as May, depending on your local climate.

Regrowing or Fresh Purchase?

If you already have tubers from last year, just pull them out of their storage space, probably in the basement. Otherwise, begonia tubers are on sale in garden centers everywhere. Some even offer small tuberous begonia plants in plug trays. They’re already growing, ready to transplant into a 6-inch (15-cm) pot. Sometimes these little plants are even in bud!

Tuberous begonia tuber with small shoots.
Begonia tuber that is starting to wake up, showing tiny pink shoots. Photo:

The tuber resembles a flattened, fleshy brown bowl, as its upper surface is usually concave. It’s in this hollow that you already see, in earliest spring, the little white or pink shoots that will become the future flower-bearing stems. When you take them out of storage, the tubers are more or less in suspended animation. They’re waiting for you to plant and water them so they can continue their growth.

Simple Planting

Hand placing begonia tuber in metal pot. Pink sprout is visible.
Place the tuber on moist potting soil, then cover lightly with more mix. Photo: iBulb

Planting is certainly simple enough. Take a 6-inch (15-cm) pot and fill it about halfway with moist potting soil. Place the tuber in the center, on the potting soil. Just make sure the concave side, the ones with the shoots on it, is facing up. Now, pour in potting soil, barely covering the tuber. Water lightly. Just make sure you don’t leave any water sitting in the hollow of the tuber. That could lead to rot. Place the pot in a moderately well-lit location at about 70 to 75°F (21–24°C) to stimulate growth.

After a week or two, the shoots with lengthen and begin producing leaves. As they grow, gradually increase watering, just enough to keep the soil slightly moist at all times. If possible, also, lower the temperature at this point to around 60°F (15°C) at night. That isn’t absolutely necessary, but it does tend to produce a stockier, denser plant.

Young sprouts and leaves of tuberous begonia
The leaves grow fairly quickly and you can then add more potting soil. Photo: Summer1810, depositphotos

When the shoots are about 6 inches (15 cm) high, add more potting soil to the container. You can fill it up to ½ inches (1 cm) from the edge. The part of the stem that ends up covered in soil will then produce roots. This will result in a stronger plant that is less likely to break in the wind.

That the flowers of the tuberous begonia are edible? They offer a delicious tangy taste to salads, poke bowls and smoothies, not to mention giving your meal some very pretty colors!

Hardening Them Off

When outside temperatures warm up, you can begin to acclimatize your begonia to outdoor conditions. Take it outside on a fairly warm day (60°F/15°C or more), placing it in the shade at first. Bring the plant inside in the evening if the temperature drops below 60°F (15°C). Repeat daily, gradually increasing the light intensity each day for a week or so. Most tuberous begonias prefer growing in partial shade. Multiflora begonias (such as Non Stops), though, can tolerate full sun.

Yellow and orange trailing begonias.
Some tuberous begonias have an attractive trailing habit and are ideal for hanging baskets. Photo: Debu55y, depositphotos

Transplanting and Care

When there is no more risk of frost and night temperatures remain reliably above 60°F (15°C), you can move them to their summer home. Transplant your tuberous begonia to the garden or to a planter. Plant hanging varieties in a hanging basket or window box.

During the summer, water and fertilize tuberous begonia as you would any annual.

And in the autumn, of course, don’t forget to bring the tuber back indoors after the first frost. You just have to keep it dry and dormant in your basement over the winter.

Other Bulbs to Start Indoors

It’s not just the tuberous begonias that sometimes need a head start indoors in the spring. The same kind of regime (planting indoors early in the spring) also applies to other frost-sensitive bulbs that you have kept stored in the basement during the winter:

  • Alocasias,
  • Callas,
  • Cannas,
  • Caladiums,
  • Dahlias,
  • Gladiolus,
  • And many others.

It’s time to wake them up too for an early start to a long and gloriously flower-filled summer!

Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, will continue its mission of demystifying gardening and making it more accessible to all.

11 comments on “Time to Wake Up Your Tuberous Begonias

  1. Elaine Greene

    I have learned so much from the “Laidback Gardener”. I read everything I can on gardening, but your column has become my trusted “go to” from composting, planting, plant issues, etc,, etc. Thank you for your expertise; it is greatly appreciated. You have helped me “progress” in both knowledge of gardening and helped my 6 gardens grow abundantly! KEEP UP THE GOOD WORK!!!

  2. Capitola used to have a Begonia Festival, back when Antonelli still grew begonias in the region. It is unfortunate that those sorts of specialty nurseries are no longer regarded like they used to be.

  3. Thanks for the feedback. Think I will just let the tuber grow, but try some pinching and propagate the pinched stems.

  4. Linda Bradley

    Should I ever split a begonia tuber or just keep putting it in bigger pots each year? I have a few of those dinner plate sized ones. Also Should I pinch them back to get bushier growth?

  5. Begonias are so easy to overwinter I am not sure why people don’t do it. I have overwintered a Begonia boliviensis for many years. The tuber is now the size of a dinner plate and puts on an incredible show every summer. Beats the little four inch pots available in Spring.

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