How to Start Tuberous Begonias in the Greenhouse
Tuberous begonias are one of my favorite summertime flowers. Striking in containers and hanging baskets, if treated right they give color all summer and into fall. These big beauties bloom in many colors and are not to be confused with the smaller wax begonias you will see later in the season sold in pony packs. The showy tuberous begonia makes a big impact.
Since tuberous begonias can be started indoors in early spring, I decided to give my begonias a jump start in my greenhouse – Starting begonias in a greenhouse.
- Choosing Good Tubers
Right around now, begonia tubers are available at home and garden centers,usually in packages of three tubers that look like this.
Starting out with healthy tubers is very important. While at the garden center, I try to examine the tubers in the package as best I can. I look past the wood chips to determine if the tubers are healthy. I look for plump, firm tubers. If a tuber feels mushy when squeezed, that means it’s starting to rot. I also look for any sign of emerging stems on the concave side of the tuber.
They usually appear at first as tiny red or pink bumps and then they start to bud out. So in this case, red or pink bumps are a good thing as this means the tuber is viable.
- Starting the Tubers in the Greenhouse
I planted the tubers in square 5-inch plastic pots that drain. I used a 50/50 blend of seedling starter mix and regular potting soil and moistened it slightly before filling the containers.
I filled each container with soil until it was about two to three inches short of the top and then placed the tuber in the middle with the root side down and the side with the emerging stems (pink bumps) up. I pushed the tuber down into the soil but didn’t completely submerge it.
Then I covered the tubers with a dusting of soil. I watered around (but not on top of) the tuber to moisten the soil. During the tuber’s time in the greenhouse, it’s important to keep the soil moist but not soggy. And since tubers can rot fairly easily, it’s also important not to have standing water on top of the tuber. So in short, water around it, not on top of it. In addition to evenly moist soil, they need lots of bright light, so my grow light will also come in handy.
Once the stems sprout a bit, I will fill more soil in on top of the tuber so that the roots can better develop. Another option at this point is to replant the tuber deeper into the soil.
- Going Outside
When the danger of frost has passed and evening temperatures stay above 50⁰F, I can replant the begonias into containers or hanging baskets and place them outside in partial shade. They should be kept evenly moist (but not soggy) throughout the summer and fertilized occasionally. I’m looking forward to the show.
About our guest writer: Heidi lives in the Seattle area with her husband, Chris. In the fall of 2014, they became the proud owners of their own Sunglo greenhouse. Read about their experiences with their greenhouse and their other home and garden projects on Heidi’s blog, My Sweet Cottage.