Growing Instructions for Tuberous Begonias
Tubers can be planted from February to June. In areas with hot summer temperatures, it is wise to have the well established before hot weather arrives.
Begonias should be planted with 1 to 1.5 inches of soil covering the top of the tuber, in well-draining beds or large pots. Partial shade is necessary in all but the coolest climates, although begonias do need some sunlight. An Eastern exposure is also acceptable, receiving full sun in the morning with afternoon shade. Any light soil is satisfactory. Humus such as peat moss or leaf mold is good for retaining moisture and creating slightly acid conditions. Begonias need to be moist at all times. Any mild fertilizer can be used at intervals throughout the season. A natural fertilizer such as fish emulsion is ideal. For best results, fertilize lightly in the first few weeks of growth, as this will promote earlier bloom. Increased nitrogen after blooming begins will help maintain greener foliage.
Tuberous begonias are tender and cannot be placed outdoors until danger of frost is past. In order to advance the planting season they may be started indoors about 8 weeks before the proper planting season. Fill a flat or box at least 2 ½ inches deep with coarse peat or loose soil. Place the tubers hollow side up with the top just below the surface. Keep the soil MOIST, but do take care not to over-water before growth is started. Optimum temperature should be from 50 to 75 degrees F (10-24 degrees C), but slightly higher or lower will do no harm. Starting at 72 degrees F is ideal to advance growth for earlier bloom. After the bud appears, the plant needs sufficient light. The begonias may be transplanted to an outdoor location any time after good root development is apparent and before the top growth is more than 4 to 5 inches tall.
Begonias prefer cool, moist conditions, so on very hot days, frequent spraying of plants with water will help maintain cool conditions.
After leaves turn yellow and the blooming season is over, water should be withheld. Tubers may be lifted and stored in a cool, dry location until planting time again next spring.
INDOORS or GREENHOUSE:
Tubers may be planted directly in pots or started as above. Pots should be at least 6 inches in diameter. Any good potting mixture will serve, or and humus and sand for good drainage to any suitable loam soil. Bright, indirect light is necessary and cool temperatures are required.