As a large group of tropical foliage and flowering plants, begonias are very popular in both indoor and outdoor gardens. Their abundant, beautiful flowers and handsome foliage make them a star in any gardener's eyes. Begonias are divided into three major groups according to their root structures: fibrous-rooted, rhizomatous, and tuberous-rooted begonias. Of the tuberous begonias, the best known come from a sub-group bred from American stock called Tuberhybridas. Although the tender tubers must be dug up from the garden and stored over the winter, they can last for 10 years with proper care.
Height & Spread
Tuberous begonias grow 12" – 18" tall, spreading 1' – 1-1/2' wide at maturity. The new compact multi-flora types grow to about 6" tall.
The showy, waxy begonia blossoms vary from red, pink, yellow, orange, and white. They come in single or double forms — bi-colored, ruffled, or smooth. They bloom during the summer and right up until frost. Male and female flowers appear separately on the same plant, and some gardeners pinch off the smaller female buds for larger male blooms.
The leaves of tuberous begonias are almost as varied as the flowers. Appearing alternately on the stem, each leaf — or in some cases, the vein — may be colored reddish brown instead of the usual medium green. Leaves are oblique and sometimes called "elephant's ears".
- Determining the Top or Bottom of Bulb: The rounded side of the bulb with roots is the bottom. The top side is the concave side.
- Sprouting Time: Usually within 4 – 6 weeks of planting. If in the ground, it can take a little longer if the temperatures are still cold.
- Bulb Preparation: Plant tubers immediately in containers.
- Shelf Life: To ensure adequate blooming time, planting should occur by mid-June.
- Location in Garden & Spacing: Begonias prefer partial sun. Cover with only 1/4" – 1/2" of soil, spacing about 6" apart. Wait until the threat of frost is over.
- Potted Plants: Plant one per 6" pot or combine together into larger pots. Leave at least 4" of spacing in between the tubers and the pot's edge. It's best to add fresh soil or increase pot size the following spring, as the tubers grow in size every year. Since trailing varieties need room to hang downwards, don't place them in the same pots as the upright varieties.
- Soil: Use regular potting or garden soil. Cover with only 1/4" – 1/2" of soil.
- Watering: Water upon planting and a couple times a week all summer.
- Fertilizer: Maintain flower size and count from year to year. For best results, use Roberta's Flower Magic Plant Food twice a month all summer.
- Lighting: Partial sun is preferable. Full sun will burn flowers.
- Temperature Zones 9 – 11: If planted in the ground, they'll come up at the right time without worry of frost damage. If planted in pots, you may place them outside and leave them there all summer when nights stay above 45°F. In the garden, they can handle temperatures down to about 35°F.
- Winter Dormancy: In late autumn, when leaves fall off and stems separate easily from the tubers, begonias are ready for storage. Cut plants back to the ground. You can leave them in containers in a cool, dark spot where temperatures remain above 35°F. Refrain from watering until the following spring. Or, lift tubers and store them in dry peat in a cool, frost-free place until spring.
- Propagating: Begonias bloom every summer from mid-June to October. After 2 – 3 years in the spring or fall, you may divide the bulbs into small divisions and replant. This is not necessary, however. At a minimum, increase pot size or add fresh soil to potted plants annually.
Frequently Asked Questions
Q: If it freezes where I live during the winter, how do I winterize?
A: In late autumn, when the leaves fall off and stems separate easily from the tubers, begonias are ready for storage. Cut plants back to the ground. Leave them in containers in a cool, dark spot where the temperature remains above 35°F. Don't water until the following spring. Or you can lift tubers and store them in dry peat in a cool, frost-free place until the following spring.
Q: Help! My bulbs are slow to come up!
A: Make sure you planted them with shallow covering — only 1/4" – 1/2"of soil. You might want to make sure that they were planted top-side up.
Q: Why are some of the flowers different sizes?
A: Male flowers are the largest, female the smallest. Usually there's one male to two females. To increase the size of the male flowers, pinch away the females. This can add 50% more size to the male flowers.