I have grown tuberous begonias from seed a few times quite successfully. I buy my seed from Antonelli's, so that I don't miss a step I've copied their instructions verbatim.

GROWING TUBEROUS BEGONIAS FROM SEED

Tuberous Begonia seed is sown in January and February. Best germination results are from seed sown February 15th to March 1st.
Begonias require soils rich in humus or other organic matter such as leaf mold, forest humus, shredded firbark or spagnum peat moss - from best to worst in the above order. To this humus material should be added light sandy loam or river sand. The usual recommended mixture is 2/3 leaf mold to 1/3 sandy loam. An alternate could consist of 1/2 well decayed forest humus or redwood soil conditioner, 1/4 sandy loam or river sand, and1/4 spagnum peat moss. Packaged seed mixes like Jiffy-Mix, Pro-Mix, etc., are excellent for Begonias. Planting medium and containers should be sterilized with steam or soil fumigant to prevent growth of fungus and weeds.
Use shallow flats or seed pans with ample allowance for drainage. Fill to a depth of one-half inch with moist, planting medium and level. Using a piece of ordinary window screen, sprinkle a thin layer of planting evenly over the surface. Sterilize soil and containers. Moisten throughly with a light spray of sterilized water. Broadcast the seed, taking care to spread it evenly over the flat to avoid overcrowding. Dusting the seed with Rootone wil make it easier to see on the dark soil.
Water carefully with a light spray of sterilized water. Do not cover seed. Cover the flats with sheets of glass and darken with newspaper (about 2 sheets thick) until germination. Seed will germinate in six to ten days at a constant temperature of 65 to 75 degrees. Fog lightly with sterilized water during the fourth day. As soon as the seed shows small white specks, the paper should be removed. Do not remove glass until after the tiny plants appear. Use extreme care in watching that the surface of the soil does not dry out at this stage of growth. Two or three days later small plants will show.
The glass should be gradually propped open and then removed. Water carefully with sterilized water as needed. Sterilized water should be used, at least, until the third leaf shows on the small plants. Then the plants may be watered with fresh water for fifteen to twenty days before transplanting.
At first transplanting, the seedlings are spaced one inch apart in flats filled to a depth of 1 1/2". When they become crowed they are transplanted again. This time they are spaced two or more inches apart. After the first transplanting. the seedlings respond very well to weekly or bi-weekly applications of fertilizer solution prepared by diluting one tablespoon of Romeo Soluble Fertilizer in three gallons of water. In five or six weeks they will be ready for potting or planting in the garden.

ANT NELLI

I have grown some very nice exhibition type Begonias from Antonelli's seed. The main thing is to get your seed from a grower instead of off the rack. The seed has to be fresh to achieve any kind of success. You don't want to go through all of the above and then be disappointed if nothing germinates. Hope this has been of some help.

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