Tuberous begonia a showy summer bloomer

Dr. Gilbert created a shaded area for his tuberous begonia experiment from benches, shade cloths and roofing material. Photos by Karen Lawrence

Dr. Bob Gilbert – Columnist

Dr. Bob Gilbert

Several years ago, I wrote about the leader of North Korea Kim Jong’s obsession about a tuberous begonia that was named in his honor.   He built multiple large greenhouses country-wide to grow thousands of his name variety called “Kimjongila” while a large portion of North Korea’s population was starving to death. It’s curious that “gila” means mad or crazy.  Shortly after writing about this I visited a friend here in Franklin who was growing beautiful tuberous begonias successfully.  So, I decided to try a few last year with limited success. The problem is that I do not have the right amount of sunlight and a limited potential growing area. It is shaded in the morning and in full sun in the afternoon.  This is exactly opposite of what is needed for successful growing.

Tuberous begonias are showy summer blooming plants perfect for high elevations and cooler locations.  They cannot stand heat or direct sunlight. For example, I have seen hundreds of them growing as bedding plants in British Columbia at Butchart Gardens that has high shade.  These plants are grown from round flat tubers.  They are convex on one side where the roots emerge and concave on the other where the plants develop.  The concave sides ae potted up.  They are not the same fibrous types of begonias sold as bedding plants in the spring.   Here in Franklin tuberous types will do well on a deck that does not get the afternoon sun or a bright porch will work.  There are now hanging basket selections that bloom continually all summer.  Non-Stop Begonias are one example. Their blooms are smaller but very showy.

 Another great feature is that the tubers can be stored over the winter to grown again the next year.  These are not annuals.  In the fall let the plant completely dry out.  Then you remove the soil and after the tuber is very dry and store it in a brown paper bag with a little peat moss in your garage or someplace cool until spring.  In the spring you will find small buds forming on the concave side of the tuber.  Place the tubers slightly submerged into tray full of potting soil.  Keep the soil barely moist.  When the new shoots are about 2-3 inches tall plant each tuber into a separate pot and cover the tuber with about ½ inch of soil and water.  Always be aware that these tubers will rot standing in overly wet soil.

female part with male
pink edged begonia
red edged
Red Tuberous Begonia

 Tuberous Begonia blooms come in all sizes, many colors and bloom configurations with both single and double blooms. Picotee selections are quite showy with thin red petal margins. Some varieties have blooms that can reach up to five inches in diameter.   The first year I had trouble growing them successfully because I had too much sun and it was too hot and humid in my greenhouse.  This year I decided to give it one more try. However, I needed to create the right environment: Namely bright but not direct sunlight, high shade.  We had an unusual amount of rain this year so I also needed to control moisture if I was going to grow them outside. I happened to have an unused greenhouse bench and some other easily assembled big box store plastic benches. I stacked them to create an enclosure.  It is not attractive but it works. Over the top to control moisture and overhead sunlight, I placed plastic opaque roofing material. Then, I ordered shade cloth from a greenhouse supplier to create a shade curtain. This was needed because my enclosure received direct sun all afternoon.  I rotated the plants about every two weeks in order to get even light because the back of my enclosures faces the wall of the garage.  All summer I moved the heaviest bloomers to the screened porch.  I would like to be able to view them all together uncovered but I do not have the right conditions for that.  They are fertilized with a weak dilution (half strength) of a liquid fertilizer every two weeks.

 One trick to get larger blooms is to remove the smaller female buds that are right beside the larger male bud. (See photo) Usually the female blooms are single and much smaller.  This directs more energy to the male bloom which enhances its size.

I have searched for the variety “Kimjongila” for sale without success. It is truly beautiful. Curious that it has not reached the commercial market.

Next year I want to try couple of varieties I do not have. Do not be intimidated by tuberous begonias. They will make you look like a master gardener. Also, being able to save the best performers for the following year is another plus.

Dr. Bob Gilbert co founder of Smith Gilbert Garden in Kennesaw, Ga.

Karen Lawrence professional wildlife and botanical photographer from Franklin.