Yard And Garden: Preparing Tuberous Begonias Indoors In Cold Weather

 

The weather is cold outside, but it’s the perfect time to start preparing and growing tuberous begonias indoors to get them ready for a move outdoors when spring arrives.

 

The process can be challenging, but here are some tips from Iowa State University Extension and Outreach horticulturists on how to best ready tuberous begonias during colder months. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

 

Tuberous begonias can be grown from seeds and tubers. Growing tuberous begonias from seeds is rather challenging. Tuberous begonia seeds are tiny. There are approximately 1 million seeds per ounce. (To make the seeds easier to handle and sow, many seed companies coat the seeds with clay or a similar material.)

 

Also, tuberous begonia seedlings grow slowly. The crop time for tuberous begonias is 18 to 20 weeks. Seeds must be sown indoors in early January to produce good size plants by spring. Because of the challenges associated with growing tuberous begonias from seeds, starting tuberous begonias from tubers is the best option for most home gardeners.

 

 

Plant tubers indoors about eight weeks before the average last spring frost in your area. Start tuberous begonias in pots or other suitable containers. All containers should have drainage holes in the bottom. Use a well-drained potting mix. When planting the tubers, place the concave or indented side upward. The rounded side is the bottom. Cover the tubers with ½ to 1 inch of potting soil. Water well. 

 

Then place the containers in a warm, 70 degree Fahrenheit location. Since the tubers are susceptible to rotting, keep the potting soil moist, but not wet. Once the tubers sprout, move the plants to a sunny window or place under fluorescent lights. Plants that don’t receive adequate light will be tall and spindly. Fertilize the plants with a dilute fertilizer solution once every two weeks.

 

Plant tuberous begonias outdoors after the danger of frost is past. In central Iowa, mid-May is an appropriate planting date.  

 

Plants started indoors or purchased at a greenhouse should be hardened outdoors seven to 10 days before planting. Initially, place the plants in a shady, protected location. The tuberous begonia foliage will burn if immediately placed in direct sun. Strong winds can easily tear the foliage or break the brittle stems. During the hardening procedure, gradually expose the plants to longer periods of sun and wind.

 

Tuberous begonias perform best in moist, well-drained soils in partial shade. Choose a site sheltered from strong winds. In the home landscape, locations that receive morning sun and afternoon shade are often excellent planting sites. Use a well-drained potting mix when planting tuberous begonias in window boxes, hanging baskets and other containers. When planting tuberous begonias, place plants at the same depth as they were grown in the container. Planting them deeper than previously grown may encourage the buried portion of the stem to rot.

 

Once planted, watering, fertilizing and deadheading are the primary maintenance practices. Tuberous begonias should be watered weekly in beds and borders in dry weather. Plants in containers will have to be watered more often. Check container-grown plants regularly (daily or every other day) and water as needed. Fertilize tuberous begonias every two weeks with a dilute fertilizer solution. Remove spent flowers to improve their appearance and encourage additional blooms.