TUBEROUS-ROOTED BEGONIA

If they're to be saved for another year, these tubers must be dug and stored in the fall. I leave them in the soil until the foliage is killed by frost, giving the plants the longest possible flowering season without in the least hurting the tuber, which can survive the first frost easily. After I dig the tubers up I rinse them off and let them dry for a few days; then I snap off the old growth. At that point I store the tubers in a container filled with dry peat moss, perlite, or vermiculite, and keep them in a cool, dry spot all winter. Ideally, the temperatures should be constant within the range of 40 to 50 degrees. (If your storage area is a little damp, I suggest dusting the tubers with a fungicide before storage.) (pgs. 277-279)

...Start them back to growth in early March. The first step is always to inspect the tubers for insects or soft, bruised spots; if the tubers aren't firm and clean, they should be discarded. Then I fill an 8 or 10-inch hanging pot with a moistened soil specially blended for container gardening [equal parts soil, peat moss, and sand, with added slow-release fertilizer]. For fullness, I plant 3 tubers of the same variety to one pot of this size. The tubers are easily damaged at this stage, so I scoop out small spaces for them in the soil, and just set them on, pressing them very lightly to establish contact with the medium. They should be sitting, rounded side down, about 1/2 inch deep. They should not be covered with soil, nor should the tubers touch one another. After planting, I move the containers into a bright spot out of direct sunlight and keep the soil barely moist for about a week while the tubers become established. At that point they're put on their regular growing-season diet: constantly moist soil and a once-monthly light dose of houseplant fertilizer, mixed with water. When the weather is warm enough, in early May, I move the pots outdoors to a spot where they're in half-day or filtered sunlight, and they bloom all summer long.

The best way to propagate tuberous-rooted begonias is by dividing the tubers. If you decide to do this, you will have to allow the tubers to begin growing in order to see where the buds, or eyes, are. I usually pot them in a shallow flat in my standard soil mix. I plant the tubers as if I were planting them for the whole season, as described above. But when the growth starts, I pry them up from the soil, working gently with a fork, and divide the tubers into one-eyed sections. Then I dust the cut surfaces of the sections with sulfur, and give them a day or two in a dry place out of the sun. When they're dry, I plant each division, eyes up, as above." [Remember that they are not covered with the soil.--Amy] (pgs. 68-70)