For bold color in shady gardens, it’s hard to beat tuberous begonias. These lush 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, they make it easy to dress up any outdoor living space.
Indoor Growing Tips
Begonias love warmth and humidity. Grow the tubers in a warm (70 to 75°F) place and cover the pots loosely with clear plastic to help retain moisture. Moist air and damp soil will encourage quick sprouting and rapid growth. Though the soil should be moist, keep the tubers themselves relatively dry so they don’t rot.
When sprouts are about an inch long, move the pots to a warm, sunny windowsill or put them under grow lights. Water as needed, keeping the soil barely moist, not wet.
Outdoor Growing Tips
When your begonias have 3 or more leaves, you can transplant them into larger containers. Be very gentle when handling them as it’s easy to break off a stem.
Plant one tuber per 6” pot or 2-3 tubers for a 12” pot. If you are planting the tubers into a window box 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 your begonias outdoors. Wait until the nights are relatively warm (above 50°F) and there’s no threat of frost.
Tuberous begonias are sensitive to the mid-day sun, which can burn the leaves and flowers. Give them partial shade (a half day of the morning or late afternoon sun is perfect) or grow them in filtered light beneath a deciduous shade tree.
Water your begonias when the soil is dry to the touch. Check often during dry, hot weather. Removing spent blooms and wilted leaves will help to keep your begonias healthy and encourage more flowers. For maximum flower production, apply a liquid fertilizer every 2 to 3 weeks.
At the end of the growing season, as days get shorter and overnight temperatures get cooler, your begonias will flower less and the foliage may begin to yellow. If you want to keep the tubers and replant them next year, move the plants to a protected location and let them gradually die back. Dig the tubers and let them air dry for a week. Then store them in peat moss, in a cool, dark, frost-free place.