Date: April 1989 (Revised April 1995)
Source: NDSU Extension Service Horticulturists
Tuberous-rooted begonias are a valuable addition to the flower border. They grow quite well in shaded areas. You can anticipate a wealth of color throughout the entire summer and early fall months.
You can get an early start by planting tubers in mid- to late-winter. Place the tubers in peat moss or a soil mix containing one part soil, one part peat moss and one part vermiculite (ver-MIK-ya-light). Cover with about 1/2 inch of the mix and set in a warm location. Keep the growing medium moist at all times.
Grow the plant in an east or north window during the winter and early spring months.
Do not give tuberous-rooted begonias full sunlight.
Some gardeners place several tubers in a small container and transplant them after new growth makes its appearance. Other gardeners plant one tuber directly in a 5- or 6-inch container.
Keep the soil uniformly moist at all times throughout the spring and use a complete fertilizer available from retail stores that handle garden supplies. Be sure to follow the manufacturer's directions.
Turn plants about once a week to get a symmetrical plant. This is important since only a little light will be available in an east window.
You can shift begonias to your outdoor garden after the last frost in the spring. This is usually in early- to mid-May. Do not bury plants any deeper in the garden soil than they were in your indoor containers.
Tuberous-rooted begonias need water. Avoid planting in heavy, poorly drained soils. It is important to prepare the soil prior to planting by using liberal quantities of compost or peat moss.
Work a 1-inch layer of material into the upper 4 inches of the bed. An ideal location is one where water drains away from the begonia bed.
You can harvest tubers in the fall after a killing frost. Remove all foliage and the stem at the soil line. Carefully remove tubers and shake off excess soil. Store in a cool basement where temperatures range from 45 to 50 degrees. You can surround tubers with very lightly moistened peat moss.
Check periodically during the winter for signs of tubers drying or rotting. Drying occurs with warm and dry storage conditions. Bulbs rot when conditions get too warm and moist.
If you have further questions, please contact your county office of the NDSU Extension Service.
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