Tuberous Begonias: How and When to Start Them Indoors
For bold summer color in a shady yard, it’s hard to beat tuberous begonias. These lush, tropical plants ask very little, yet bloom so prolifically. Their elegant, rose-like flowers dress up any outdoor living space and are an ideal choice for window boxes, hanging baskets, decorative urns or even garden beds. Imagine how great they would look at your house!
An Early Start is Essential
For tuberous begonias to reach their full flowering potential, they should be started indoors, 8 to 12 weeks before you move them outside. Growing the tubers is a fun late winter project. Just line them up on a windowsill until they sprout, then plant them in small pots. Warmth, light and a little moisture is all they need. Here’s a schedule to help you know when to get started (don’t know your growing zone? Click HERE)
- Growing Zone 10: Indoors: Late December; Outdoors February
- Growing Zone 9: Indoors: Early January; Outdoors: Early March
- Growing Zone 8: Indoors: Early February; Outdoors: Early April
- Growing Zone 7: Indoors: Late February; Outdoors: Late April
- Growing Zone 6: Indoors: Mid-March; Outdoors: Late May
- Growing Zone 5: Indoors: Mid-March; Outdoors: Late May
- Growing Zone 4: Indoors: Late March; Outdoors: Early June
- Growing Zone 3: Indoors: Late March; Outdoors: Early June
What the Tubers Look Like
Begonia tubers are firm, dark brown and slightly hairy with an irregular shape. If you look closely, you’ll see that one side is domed and the other is slightly concave (like a bowl). Most of the tuber’s eyes (which will sprout into stems and leaves) are clustered inside the bowl. When you plant the tubers, they should rest on the domed side, with the eyes facing up.
How to Plant Tuberous Begonias
Like most bulbs, tuberous begonias have a winter resting period. When your bulbs first arrive, especially if it’s before March, they may still be dormant. For best results, you’ll need to wake them up before putting them in the soil. Simply place the tubers (bowl side up) on a windowsill or on a tray in a warm room where they’ll get bright, indirect light. Watch closely and you’ll see the eyes get pink and gradually become more prominent. Once you see the first sprouts, it’s time to plant.
The tubers may be planted in peat pots, small plastic pots or a shallow seed starting tray. Put 2-3” of moistened growing mix in the bottom of the container and set the tubers on top (sprouts up) about 3” apart. Cover with 1-2” of moistened growing mix and then water lightly to settle the tubers.
Where to Grow Your Baby Begonias
Put your newly potted begonia tubers in a warm (70 to 75°F) place. Cover the pots loosely with clear plastic to keep the soil lightly moist (not wet). The tubers themselves should stay relatively dry.
When the sprouts are about a half inch tall, move the plants to a warm, sunny windowsill or put them under grow lights. Water as needed, keeping the soil just barely moist and letting it dry out between waterings.
Transplanting and Moving Your Begonias Outdoors
When the tubers have 3 or more leaves, it’s time to transplant them into larger containers. Be gentle, as it’s very easy to break the stems to off the tubers. If this happens, you can try rooting the broken stem in a glass of water. This doesn’t always work, but other stems on the tuber can take over.
Plant one begonia tuber per 6” pot or 2-3 tubers in a 12” pot. If you are planting the tubers in a window box or garden bed, plant them approximately 8” apart. Using slightly bigger pots that hold more soil will make it easier to keep up with summertime watering.
Don’t be too eager to move your begonias outdoors. Wait until the nights are relatively warm (above 50°F) and you’re confident there’s no threat of frost. Give the plants at least a week to make the transition from indoors to out. During this time, keep the pots in a place where they will be protected from sun and wind.
Ready to give it a try? Click HERE to choose which begonias you want to grow. To learn more, we also offer this article: All About Begonias.
Tried them last summer. I was supposed to get large flowers but only got small single flowers. Did I buy the wrong ones?
Hi Jane – Tuberous begonias produce male and female flowers. The doubles are male and the singles are female. It’s normal for the plants to have some of each — usually there are many more doubles. Did you purchase your begonia tubers from Longfield Gardens? If so, they should definitely have produced lots of double flowers. Please contact our customer service department at info@lfgardens.com
I have two pots white begonias planted indoors from last year. Can I plant them by themselves? Do I need to mix them with other Begonias?
Hi Eilasor, You can plant one tuberous begonia per pot or plant several of them together in a larger pot. Enjoy!
Is it okay to start them in full size pots to avoid transplanting later on?
Hi – Sure, that will work. We recommend starting in small, shallow pots because they’re easier to manage indoors. In a big pot you’ll need to take extra care not to overwater.
Hello, is it okay to simply leave them in the hanging basket they were purchased in? I removed all the leaves and stems in the fall and brought the baskets to my garage for the winter. Can I simply start them inside from the basket? Maybe add some nutrients? This is my first time and I don’t have a green thumb but I did buy a moisture/light/pH gage…would that help?
Hi Jordan – as long as the tubers didn’t freeze and are still firm like a potato, you can grow them again in the same hanging basket. They will just need some fresh soil. Purchase a small bag of top quality growing mix. Dump the contents of the pot out onto a flat surface or into a paper bag. Separate the tubers from the old soil. Throw out the old soil. Moisten the new growing mix thoroughly – it should feel like a damp sponge. Refill the basket with fresh soil and settle the tubers back into the soil (not too deeply – follow the planting instructions). Get them started now, so you’ll have flowers by June. Enjoy!
Hello
How many begonias would you recommenced I plant for an 18inch hanging planter? I bought two 10 inch baskets of Begonias that I would like to transfer but the 18 inch basket is quite a bit deeper as well as wider.
Thank you!
Hi Vanessa – We have an article on our website with some suggestions (scroll to the bottom) about container size: How to Grow Summer Bulbs in Containers. We recommend one begonia tuber per 10″ basket, so I think it will be just fine to grow two tubers in the 18″ basket. The extra depth will help keep the basket from drying out too quickly.
Hello, mid April my husband bought begonias hanging baskets from Costco, GTA. Till date i have kept those inside. I want to know when can i move them outdoors and best procedure to do that. Even the care and pruning information if possible. I am a beginner in plant care.
TIA
Hi – On our website you’ll find several articles about growing begonias, like this one: All About Begonias. Begonias are very cold sensitive, so if possible, don’t put your plants outdoors until nights are the the 50’s.
I bought garden ready plug plants of begonia illuminations. Grown from seed. On removing them from their pplots they seem to have become tubers Can I grow these? Thanks.
Hi – Yes you can. The plants you purchased were probably grown from cuttings and over the past growing season they developed tubers. If you are successful in saving these tubers until next spring, you should be able to get them to sprout and grow into new plants. Good luck!
We planted some new bulbs and are waiting for them to sprout. Did we make a mistake by not letting them sprout first? Somehow we did not see that they would sprout on their own outside of a pot.
Hi – They should sprout just fine as long as they are not planted too deeply and you don’t over-water. If you want, you could also gently pull away some of the soil on top of the tubers and then re-cover as the first leaves develop.
Two questions…how much sun can they tolerate? I have planter boxes hanging off the rail of my East-facing deck I was hoping to fill with them. Should I switch to hanging baskets under the eaves? Also, I’m southeast of Seattle and it looks like nighttime lows are predicted to drift into the 40s at least through mid-May. Should I wait to plant the begonias until late May?
Hi Carol – In your area, tuberous begonias should grow well in morning light. They will not be happy in direct mid-day or afternoon sun. Ideally you would get your begonias started in March/April and then plant them outdoors as young plants with several sets of leaves. If possible, start the tubers now as instructed in the article and transplant them outdoors in late May when nights are reliably 55-60°F.
I have a beautiful hanging begonia that produces tiny, bright pink flowers. Will it still produce if it gets light 25/7? It’s on our front porch and we keep the light on all night.
Hi Mary – I’m sorry, but I don’t know the answer to your question. I suspect they will be fine, but time will tell. I did find an old Cornell study about the effect of day length on begonias – you may find it interesting: https://hortscans.ces.ncsu.edu/uploads/d/a/daylengt_53a1c1a0f09d3.pdf
I purchased 20 tuberous begonia bulbs from you last March. I planted them indoors in a roll around self water garden planter on 3/24. They started popping thru the soil on 4/17. I rolled the planter outside on my covered deck when the night time lows were in the mid 50’s in late May. I have kept the soil constantly damp and have fertilized with Miracle Grow every 2-3 weeks, They are now beautiful plants 10-12 ” tall. They show no signs of flowering. No buds at all yet. What am I doing wrong? too much fertilizer? should I pinch off the top leaves? Be more patient? HELP!
Hi John – I am not a tuberous begonia pro, so I’m not exactly sure what’s happening. Though tuberous begonias will flower in the shade, they do need some sun. Are yours getting a few hours of sun each day? This may be especially important at the start of the season. Also, try letting the soil dry out a bit between waterings. Sometimes this encourages plants to set buds.