I needed some showy flowers for three large containers near our front door and decided to try tuberous begonias. Here’s what happened.
In late March the tubers were planted indoors in 5-inch peat pots, with an inch of dry planting mix on top of each tuber. The pots were soaked in a tray with an inch of water, but after that kept just barely moist until leaves started to appear. This took a while: some tubers sprouted after a couple of weeks, and others took as long as six weeks, but all grew eventually. Sprouts were fed every other week with half strength liquid fertilizer.
In mid-May I transplanted two begonias to each large (18-inch diameter) outdoor container. The top inch or so of each peat pot was removed before planting (if any portion of a peat pot is above the soil line it will act as a wick sucking moisture from the roots). Plants on the north side of the house were fine after transplanting, but those in another container that got strong afternoon sun ended up with scalded leaves, and never did totally recover.
The plants were fed monthly with a slow release fertilizer. Three to four inch double flowers started to appear in late June and continued until the first frost. Spent blooms were removed regularly to encourage more flower production. Some plants got so top-heavy that they started to heave out of the soil and had to be propped up with bamboo stakes.
Each container had one red and one yellow begonia; even though the catalog stated that they were the same size the yellow plants were quite a bit shorter, on average. I made diagrams showing the location of each color in each container, so that when the tubers were dug up after the first frost I knew which was which. They were air dried for a week or so then stored indoors in peat moss in plastic bags.
Next time I’ll plant the tubers a month earlier. This will give them more time to sprout, and allow time for hardening off to avoid the leaf scalding issue. I should be able to get them outside sooner and hopefully have earlier blooms. And I’ll plant only one color in each container so that the larger plants don’t dwarf the little guys.
Jim Janke is an Extension Master Gardener Volunteer in Haywood County.
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