Summary: Tuberous begonia care is simple. Follow a few rules in your care – direct sunlight, well-drained soil, and water. Soon bulbs full of colorful, showy bloom will fill a pot or hanging basket, raining color on the landscape.
Question: My mother made tuberous begonia care simple. Her pots and hanging baskets of “tubular begonias,” as she called them, showered our patio with summer bloom and color during their season.
Unfortunately, Mom is no longer around to share her tips on how to care for tuberous begonias. Can you give me some care and growing tips to start my begonia growing legacy? Carla, Baltimore, MD
Answer: Growing beautiful tuberous begonias (Begonia tuberhybrida or Begonia x tuberhybrida) is not as difficult as many gardeners, especially beginners, seem to think.
In fact, one needs only to keep to a few basic rules to ensure healthy bedding plants that will be the center of attention in your neighborhood.
After you have had just a little success growing these tender perennials, they will become a hobby within a hobby. That is how it happened to me.
Growing Success First Time Out!
I first tried growing these colorful bulbs about 15 years ago in Maine. The front of our house was shaded by some huge elms and horse chestnuts.
As I loved color, I tried all varieties of partial shade-loving flowering plants but soon found out I was wasting my time.
The thought of tuberous begonias came to me, so I purchased but a few tubers, as it was expensive to fill a 60-foot front.
Fortunately, I had fairly good luck, though the begonia bulbs I overwintered for the next year rotted on me when I started them the following Spring.
It was due, I later found out, to insufficient warmth – these shade-loving plants need a temperature of about 70° degrees Fahrenheit.
Since then, with that temperature reading, excellent results have been obtained by starting them in the cellar.
Start Early For Early Flowers!
To ensure early flowers, start planting tuberous begonias indoors at any time from late February to mid-March. Mine always started about March 15 at my home in Massachusetts.
When growing begonia tubers, it’s best to start in early spring or late winter.
To avoid confusion later on, it is best to keep colors separate (keep that special hybrid apart to show it off in a pot by itself).
As the yellows develop more slowly, they need to be started before the reds, which grow more quickly. Plant them with the depression end up – the top of the tubers in pots, trays, or flats.
I use the smaller 3-inch deep flats for the potted plants, as they are easier to handle. A mixture of equal parts sand and peat moss is suitable, and it is important not to plant them too deeply.
The little begonia tubers always present a problem. As they are so small, it is difficult to determine which end is the top, and if they do not sprout within a certain time, they should be dug up to see if they have started.
A bulb planted upside down must grow its shoot downward first and then up, while the roots at the top have to grow downward.
Even though I have been growing other types of begonias for years – rex begonias and Geiger begonias – I still find it hard to be certain which end is the top and which is the bottom.
More on: Rex Begonia Care
Start Tuberous Begonia Bulbs In A Warm Place
As already mentioned, when it comes to growing tuberous begonias, the bulbs need warmth at the start. Remember, they thrive in USDA hardiness zones 9 to 11.
Some of mine are started in the basement and some in the kitchen, although those in the basement need to be brought to bright light when the sprouts appear.
They stay in their original flats until the sprouts have started. Then they are transplanted into 4-inch pots or containers and placed in my small greenhouse in Maine.
Why does this matter?
Until the addition of the greenhouse, equal success was obtained by placing the flats in a garage with a large window.
My very first plants were placed in window boxes in front of the house. When I decided to set them in the ground as well, I realized the roots of the trees presented a problem, so I decided to plant them in pots.
Here’s the deal…
Growing begonias in pots, it was possible to prepare the potting soil or fresh potting mix thoroughly for each plant and to arrange the pots in the ground in such a way as to produce the best effect and floral display.
Now the pots are arranged in tiers, starting with the drooping kinds in the window boxes and working downward to the lowest specimens at the front of the border.
In this way, the flowers show up to better advantage. For more contrast of color, I keep the reds, yellows, whites, and other colors in separate groups.
This Begonia Soil Mixture Never Let’s Me Down
I like 8″ inch clay pots or seed pans for each bulb. In fact, the containers cannot be too big.
My soil mixture consists of the following:
- One part of rotted manure
- One part peat
- Two parts light, gravelly soil – sand is added if the soil is clayey
- A handful of bonemeal with the same amount of balanced chemical fertilizer for each wheelbarrow of the mixture.
For good drainage, rocks or broken clay crocks are placed at the bottoms of the pots.
These drainage holes on the bottom allow the roots to breathe and excess water to drain freely.
This is very essential, for if plants are kept too wet, the flower buds and blossoms drop – a difficulty every beginner soon learns.
My experience shows that the crispers drop their blossoms the most, though I do not know why.
The camellia-flowered types hold theirs the best.
Wetting the foliage, especially if it is dusty, is a good practice. In my place, I also find that the elm seed which falls on the green leaves will cut a hole through them if they are not washed off periodically.
Moreover, Tuberous begonias are heavy feeders, so apply a slow-release fertilizer throughout the growing season to encourage consistent flowering.
Protect The Begonias From The Enemy – Wind
My indoor plants start to flower about the first of July and are at their peak during August, although flowers last until well after the 15th of October.
To rest the houseplants sufficiently, watering should be withheld after Labor Day. Otherwise, they will remain tender.
A great enemy of tuberous begonias in the garden is the wind. As I am near the ocean, it is one of my worst problems.
I have plenty of shade and would like to grow more begonias, but the wind is the foe that needs reckoning.
However, to counteract it at the front of the house, I have recently planted an arborvitae hedge to cut out the wind from the northwest.
At the same time, the hedge permits the air to circulate, an important need, as tuberous begonias resent stagnant air.
Begonia Care Winter & Fall
A killing frost determines the time the stems are to be cut in the Fall. After it strikes, the tubers are dug, and the stems are cut off an inch from the base.
Then they are dried until the soil can be cleaned off, and the stem is cut back to the tuber.
For the winter, they are simply stored in paper bags. Place the colors in plastic bins with no peat moss, vermiculite, or sand to keep the colors separate.
They must be kept fairly dry, so they will not rot, yet not too dry so they will shrivel.
Moreover, tubers can be left in the ground over winter in frost-free climates.
Diseases and pests with me are few, but although rare, powdery mildew may become a potential problem.
The 15 percent yearly loss of tubers is due primarily to a white grub that eats out the inside. When planting the bulbs, I never sterilize the soil, though it is a safe practice.
Begonia Tubers Live for Years
I now have about 200 bulbs, some 10 years old. These simply keep on growing larger and larger, so I find it difficult to locate large enough pots for them.
I do not like to propagate them by cutting in sections, as they only seem to grow roots on the side that was not cut. But if you want to try to grow them through stem cuttings, it’s all up to you.
Tuberous begonia care for me has come down to simply following the steps I have outlined and trying some things out each year to improve.
Tuberous Begonias FAQ
How and when do you dig and store tuberous begonias? WG., Ind.
Allow tubular begonia to remain in the soil until after the first killing frost. Then lift the tubers leaving any soil that clings to them.
Store in a cool, dry place until thoroughly cured. This usually takes until December.
Then remove the soil and dead roots and store them in dry peat or a similar substance until time to replant in the spring or after the danger of frost has passed. Tubers will benefit from a spray of Wilt-Pruf (amazon).