For bold color in shady gardens, it’s hard to beat tuberous begonias. These lush, heat-loving plants have attractive foliage and big, rose-like flowers that bloom continuously from midsummer to frost.
Planted in window boxes, hanging baskets, decorative urns or garden beds, tuberous begonias make it easy to dress up any outdoor living space. Imagine how great they’d look at your house!
An Early Start is Essential
For tuberous begonias to reach their full flowering potential, they need to be started indoors, about . The tubers require warm, moist growing conditions to sprout and in most parts of the country, springtime temperatures are just too chilly.
Growing the tubers indoors is a fun project and an inexpensive way to get a lot of beautiful plants. Allow 6 to 8 weeks indoors. The chart on this page will tell you approximately when you need to plant the tubers, based on your growing zone.
What the Tubers Look Like
Begonia tubers are firm, dark brown and slightly hairy with an irregular shape. If you look closely, one side is domed and the other is slightly concave. Most of the tuber’s eyes (which will sprout into stems and leaves) are clustered inside the concave area. When you plant the tubers, they should rest on the domed side, with the eyes facing up. For photos, see here: Which End is Up?
How to Plant Tuberous Begonias
You can start the tubers in peat pots, small plastic pots or a shallow tray. Put 2-3” of moistened growing mix into the container and set the tubers on top (sprouts up) about 3” apart. Cover with 1-2” of growing mix and water well to settle the tubers.
Where to Grow Your Baby Begonias
Put your newly potted begonia tubers in a warm (70 to 75°F) place and cover them loosely with some clear plastic to retain moisture. Moist air will encourage quick sprouting and rapid growth. The soil should be moist, but the tubers themselves should stay relatively dry so they don’t rot.
When the sprouts are up by about a half inch, move the plants to a warm, sunny windowsill or put them under grow lights. Water as needed, keeping the soil moist, but not wet.
Transplanting and Moving Your Begonias Outdoors
When the tubers have 3 or more leaves, they’re ready to be transplanted into a larger container. Be very gentle as it’s easy to break the stems.
Plant one tuber per 6” pot or 2-3 tubers in a 12” pot. If you are planting the tubers into a windowbox or garden bed, plant them approximately 8” apart. Using slightly bigger pots that hold more soil will make it easier to keep up with summertime watering.
Don’t be too eager to move the plants outdoors. Wait until the nights are relatively warm (above 50°F) and there’s no threat of frost.