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How to Grow Tuberous Begonias

By: Kristin Beane Sullivan
Learn the secrets to growing gorgeous tuberous begonias. See how to choose the best varieties, start (and save!) the tubers every year and how to keep them looking their best all summer long.

Tuberous begonia Golden balcony: Golden Balcony tuberous begonias bloom in beautiful shades of orange, peach and yellow flowers from spring to frost.

Turn heads with tuberous begonias

Hang a few baskets of tuberous begonias (Begonia tuberhybrida) on your front porch and you’ll notice that folks will slow down as they pass to enjoy the begonias. Wouldn’t the showy blooms here make you take a second look? Once tuberous begonias start blooming, they can flower continuously for four months. Here’s how to grow tuberous begonias.

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Tuberous-Begonia-collage

Tuberous begonias come in many colors, sizes & habits

Once you decide to add tuberous begonias to your garden, you’ll have lots of options to choose from. First, there are upright and pendulous forms. The uprights usually grow 6 to 12 in. tall, but some can reach 30 inches. Pendulous forms are particularly well-suited to hanging baskets and have branches that can drape over a pot’s edge by 18 inches or more.

Upright vs. pendulous forms of tuberous begonias

Your choices don’t stop there. You can find solid bloom colors in clear white and brilliant orange, red, pink and yellow. With hybridizing, there are bicolors, or flowers with two colors, and picotees, with petals edged in contrasting colors. In addition to flower variations, there are many shades of green, burgundy and bronze foliage.

How to grow tuberous begonias

Tuberous begonia plants grow from a tuber, an enlarged stem that stores food for the plant. It looks like a bulb or a corm. Start tuberous begonias from dormant tubers in winter or spring or you can buy them in the spring as started plants.

Growing-tuberous-begonias: Plant tubers in small pots of damp peat moss. Turn the plants every week so they grow evenly toward the light. If any flower buds form at this stage, pinch them off .

How to start begonia tubers

  1. Select firm tubers with brown skin and a depression on the top side and choose a spot that’s about 70 degrees F, with bright, filtered light — an east window is good. Set the tubers, depression side up, on damp peat moss eight to 10 weeks before the last frost.
  2. Water the peat moss sparingly until the tubers sprout, then keep it slightly moist at all times.
  3. The first growth is small roots all over the skin. Then pink sprouts will grow on top of the tuber. Some tubers start to grow right away; others take weeks. Pinch off all but two or three sprouts as they grow. When the sprouts reach 1 to 2 in. tall, like the ones in the back in the photo above, it’s time to transplant.
  4. Until plants are a few inches tall, pinch off any flower buds that form so energy isn’t taken from the young plant. When the pendulous varieties have 2 in. of growth, pinch out the primary growing tip to encourage gracefully hanging branches.

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Sparks-will-fly-tuberous-begonia-containers: Try planting single specimen tuberous begonias like Sparks Will Fly above in matching containers for impact.

How to keep tuberous begonias looking good

  • Wherever you plant them, begonias like light, well-drained soil.
  • A good rule of thumb is to keep 2 in. between the tuber and the pot edge.
  • Begonias prefer morning or late-afternoon sun — direct, hot sun can burn the foliage and flowers. Too much shade can cause them to grow spindly.

Don’t forget to feed

Feed begonias after you see flower buds. Use a weak solution of a low-nitrogen/high-phosphorus fertilizer at two-week intervals.

Male-and-female-flowers-on-tuberous-begonia: If you’d like bigger double flowers and more of them, pinch off  the female buds as they form beside each male flower.

Get bigger flowers

Tuberous begonias have male and female flowers. Pinch out the single female blooms so plants can put more energy into the petal-filled double male flowers.

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Tuberous begonia root rot: Stem rot is a common problem with tuberous begonias caused by overwatering.

Tuberous begonia problems

Begonia stem rot and mildew are caused by the same fungus. Fortunately, you can control both by watering only the soil and not the foliage, letting the soil dry between waterings and providing good air circulation. Pinch off brown, water-soaked stems or leaves. The same goes for white mildew patches. Then spray right away with a fungicide.

How to save tuberous begonia tubers over winter

  • Simply take potted plants indoors to a sunny window.
  • When the foliage wilts after the first frost, cut the plant off at the base.
  • Turn the pot on its side so it won’t collect water and store it where it won’t freeze.
  • Dig the tuber and let it dry for a week before storing it in wood shavings in a paper bag. Tubers store best at 45 to 55 degrees F; a heated or attached garage or cool basement are good locations.
  • Through the winter, if you find any tubers that are rooting or rotting, change the shavings and move them to a drier location for a few weeks. If any are shriveling, moisten them with a spray of water.
Published: Aug. 13, 2020
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