Tuberous begonias (Begonia)

The most spectacular of all are the Begonia tuberhybrida, which grow about 10 to 12" (25-30 cm) tall and have rose shaped double blooms up to six inches wide. They are suitable for pots, window boxes, hanging baskets, and beds or borders. Tuberous begonias are available in a variety of flower colors, forms, and growth habits. Blossoms may be single or double, plain or ruffled, and are available in white, pink, red, orange, yellow, and bicolors. Plants may be upright or trailing.

Two other forms of tuberous begonias are Begonia multiflora, which has smaller but more plentiful flowers and grows about 8-10" (20-25 cm) tall, and Begonia pendula, which is a hanging type and ideal for baskets.

Selecting plant or tubers

When purchasing plants, select stocky plants with green, healthy foliage. As with tuberous begonias started indoors, harden the plants outdoors for a few days before planting.

Tubers for all three of these types of Begonias are available in majority of garden centers and nurseries. Choose only firm tubers and look for those with tiny sprouts showing on their upper, concave surfaces. Examine the tubers carefully for soft spots or rot before purchasing.

Planting begonia tubers

Tubers can be started indoors or planted directly outdoors in May. Since flowering typically begins 12 to 14 weeks after the tubers are planted, most home gardeners start them indoors to maximize their bloom period.

Prepare seed trays or small clean pots about 2 to 3" (5-8 cm) deep with adequate drainage holes with a mixture of good organic compost. If you're using commercial potting mix, mix it with equal parts of peat moss and sand or perlite.

Place each tuber hollow side up just below the soil level. The tuber should have no more than ½" (1 cm) of light soil covering it, as they rot easily if planted too deep. Water the tubers once really well, to wake them up, and place them in a warm, bright spot where the temperature will never fall below 16-17°C (60°F). Cover the freshly-planted tubers with paper or polythene to promote growth, but remove the covering as soon as growth appears. Don't water again until you see some growth or the soil is quite dry; the begonias don't have any roots yet and you don't want to drown them. Some begonias will sprout right away others will take weeks; generally, expect to see growth shoots in five to six weeks.

General care

Once the shoots are showing, water regularly, never allowing the soil to dry out. Give maximum light, but shade from direct sun. Applying liquid plant food will improve your Begonias' growth; feed them with half strength balanced fertilizer the first time when their leaves and stems are about 3" (8 cm) tall, wait two weeks, and then start a regular feeding schedule. When the shoots are 6 inches (15 cm) tall, the begonias are ready to be transplanted to the garden or outdoor containers. Don't put them outdoors, though, until all danger of frost has passed, and remember to harden them off properly.

Tuberous begonias thrive in partial to full shade and need well-drained soil. They need to be kept away from hot sun and drying winds. As they dislike dry conditions, they'll need to be watered generously, especially during hot weather. Keep their soil moist but not soggy; the tubers will rot if they get too much water. Always water the soil around the plants rather than the plants themselves, if possible, to avoid mildew, and at the first sign of a white patch on any of your begonias' leaves, apply a fungicide right away. Feed Begonias with a well-balanced plant food every 2 to 3 weeks.

For appearance's sake, pinch off extra or too-long stems as the plants are developing, keeping the three strongest stems and pinching off the others. Large flowered begonias look best with fewer, larger flowers, and you don't want your begonias to get leggy. Pinch off the early developing flowers, too, until the plants are 10" (25 cm) tall.

You'll also want to deadhead all your begonias regularly; removing wilted leaves and flowers encourages them to produce more blooms. The large-flowered types of Begonias should be staked.

Overwintering

Carefully dig up the tuberous begonias within a few days of a killing frost. Leave a small amount of soil around each tuber. Cut off the stems about 1" (2-3 cm) above the tubers. Place the tubers in a cool, dry area to cure for 2 to 3 weeks. After curing, shake off the remaining soil and bury the tubers in dry peat moss, vermiculite, or sawdust. Store the tubers in an area with a temperature of 40 to 50°F (5-10°C). Do not allow the tubers to freeze.