Tuberous begonias are popular flowering plants for shady, protected sites in the home landscape. Generally, sites that receive morning sun and afternoon shade are the best planting locations. Tuberous begonias are commonly planted in pots, window boxes, hanging baskets, and in beds or borders. They are available in a variety of colors, flower forms, and plant habits. Blossoms may be single or double, plain or ruffled. Flower colors include white, pink, red, orange, yellow, and bicolors. Plants may be upright or trailing.
Plant the tubers of tuberous begonias indoors about 8 weeks before the average last spring frost in your area. (Tuberous begonias can also be grown from seed. However, seed must be sown in late December or January in Iowa.) Carefully examine stored tubers before planting. Discard any that appear to be soft or rotting. When purchasing tuberous begonias, select large firm tubers. Small tubers will produce smaller plants with fewer flowers. Start tuberous begonias in pot or other suitable containers. All containers should have drainage holes in the bottom. Use a well-drained potting mix. When planting the tubers, place the concave or depressed side upward. The rounded side is the bottom. Cover the tubers with approximately 1/2 inch of potting mix. Water well. Then place the container in a warm, 70 F location. Since the tubers are susceptible to rot, keep the potting soil moist, but not wet. Once the tubers sprout, move the plants to a sunny window or place them under fluorescent lights. Plants that don t receive adequate light will get tall and spindly. Fertilize the plants with a dilute liquid fertilizer solution about once every 2 weeks. To acclimate the plants to outdoor conditions, harden the plants outdoors 7 to 10 days before planting. Initially, place the plants in a shady, protected location. Strong winds are of special concern. Strong winds can tear the foliage or break the brittle stems. Bring the plants back indoors if a frost is possible or storms are forecast. Gradually, expose the plants to longer periods of sun and stronger winds. Plant tuberous begonias outdoors after the danger of frost is past. In central Iowa, tuberous begonias can be planted outdoors in mid-May.
This article originally appeared in the February 23, 2001 issue, p. 14.