Growing Tuberous Begonias

Upright begonias like this one are the perfect plant to add show-stopping color to your garden. 

The begonia tuber that produced the flowers in the photo above.

With up to 8-inch, showy flowers that bloom from summer to fall, tuberous begonias provide all-season color to the shadier parts of your garden. Breeders have created various classes of tuberous begonias, which are distinguished by the flower's form. Flower color ranges from pure white to the deepest crimson. There are even picotee types that feature contrasting colors on the petal edges. Cascading varieties look beautiful planted in baskets hung on decks or patios, or suspended from the branches of a large tree. Look for varieties like the Illumination series, pendula hybrids, or Begonia Boliviensis hybrids. Upright forms grow about a foot tall. and can be used in planters or along the edge of a walk. Look for varieties like “Nonstop upright,” “Bertini,”  or “double” begonias at your local garden center. 

How to Plant Begonias

Tuberous begonias are native to high altitudes growing conditions in the Andes Mountains. They perform best when grown in a similar environment with high humidity and cool nights. Tuberous begonias do not grow well in hot, arid environments without special care. Though they need to be shaded from hot sunlight, like most plants they do need some sun to flower best. Morning light or light that is filtered through leaves or a lattice roof is best for these delicate beauties.

It may take up to three months from planting the tuber to full bloom, so tubers should be started indoors at least a month before the last frost date.

1. Set tubers 1 inch apart, hollow side up, in shallow pots filled with moistened potting soil in a 70-degree room. Cover each tuber with about an inch of potting soil. Water thoroughly only once to stimulate growth, but do not let the soil dry out completely. Again, a humid environment is best. A humidity dome can help retain moisture until your tubers have sprouted. 

2. Once the sprouts are 1 to 2 inches long, re-pot the tubers in 6-inch pots, or their permanent containers. Use a light, moisture-retentive growing mix and cover the tubers with no more than 2 inches of soil.

3. To produce fewer, but larger flowers, pinch off all but a few of the young stems. For a bushier plant, allow all the buds to develop into stems.

Begonia Care

1. After the danger of frost has passed, move containers to a partly shaded outdoor location away from any strong winds. If planting in beds, set begonias 8 to 12 inches apart. Plant in a location that gets early-morning or late-afternoon sun.

2. Fertilize with a slow-release fertilizer like our Gardener’s Best Flower Fertilizer to ensure flowering throughout the season. Begonias enter dormancy in the late summer so cut back on fertilizer a few weeks before that time. 

3. Keep containers moist, but avoid overwatering, which may cause the begonia stems to rot. These shady ladies are very susceptible to powdery mildew disease, so avoid overhead watering and keep the foliage as dry as possible. Use a soaker hose, drip irrigation or self-watering containers for best results.

4. Deadhead plants regularly to reduce the threat of disease. For an exotic effect, snip a flower and float it in a bowl of water indoors.

5. For most gardeners: in the fall before frost has nipped the plants, remove tubers from containers or beds and let them dry in an airy, shady place indoors. Tuberous begonias are cold-sensitive and will survive outdoors only in frost-free areas of USDA hardiness zones 9 and 10.

6. After the tops dry, remove them and store the tubers in dry peat moss in a cool, dark place with temperatures between 35 and 45 degrees F. In late spring, begin the cycle again starting tubers indoors about a month before last frost.