Starting A Tuberous Begonia

Tuberous begonia is undoubtedly one of the most popular begonias grown around the world, according to the American Begonia Society. While this begonia variety can be started from tubers, it can also be started from seed with a little effort and plenty of time for the seedlings to grow. Follow these steps to grow tuberous begonia from seed.

Step 1: Obtain Tuberous Begonia Seeds

While seeds can be harvested from tuberous begonias in the garden, the most reliable seeds come from commercial seed companies that have a few varieties of begonias. According to the American Begonia Society, sometimes this is the easiest way to obtain seeds of the newest species.

Step 2: Prepare Fluorescent Light Setup

Seedlings won’t grow unless they have an adequate amount of bright light. In most instances, this requires a fluorescent light setup because the idea is to provide a constant, even source of light. Just sticking a growing tray on the windowsill probably won’t suffice. The seedlings that do come up will likely be spindly and leaning to one side. Use a shop light and inexpensive, cool fluorescent lights.

Step 3: Prepare Mix For Starting Seeds

To grow seeds, mix equal parts of peat moss and perlite. Some experts, including the American Begonia Society contributing writer, Brad Thompson, like to use one part peat moss to 1/3-part perlite. Sprinkle some vermiculite on the top. Other gardeners like to use Miracle Grow^TM potting mix, since it already contains fertilizer.  

Step 4: Sterilize Pots

Use a hot water and bleach solution to thoroughly sterilize the growing pots or containers. Allow to dry. Note: Small pots (1-1/2 inches in diameter) work best, rather than trays.

Step 5: Fill Pots With Potting Mixture

Pour potting soil mixture into the pots and gently tamp down to about ¼-inch below the rim. Then put the pots in a tray filled with water and allow the water to soak up through the potting soil mixture.

Step 6: Placing Seeds In Seed Trays

This step is a bit tricky as seeds of the tuberous begonia are so tiny they’re like specks. Pour out a small amount on a piece of white paper and use the paper to roll the seeds off onto the potting soil mixture. Use a few to each pot, since tuberous begonias seem to like a little company. Too few and they won’t grow, while too many will crowd each other out. Do not press the seeds into the soil. Gently mist the seeds to set them.

Step 7: Place Planted Pots In Enclosed Container

Brad Thompson recommends putting the newly-planted tuberous begonia seed pots in a larger container such as a plastic shoebox with a lid. This ensures the right type of humidity under the fluorescent lights. Paper towel or newspaper is good to line the shoebox to catch any moisture from the bottom of the pots.

Step 8: Set Under Lights

The final step is to set the pots in their shoebox-type growing greenhouse under the fluorescent lights. Starting in a warm bright spot is crucial. Keep the lights on for at least 14 hours. Some gardeners leave the lights on all the time. Tuberous begonia seeds should start to sprout anytime between 4 days and a month, depending on variety.

Step 9: Wait To Transplant

Tuberous begonia seeds that come up need to have at least one leaf that’s about a ½ inch around before they’re ready to transplant into individual pots. Don’t rush them.