How to Grow Begonia

Begonias do best in shady or partial shade locations. They can tolerate the morning sun, but the afternoon sun is too harsh for them. According to Clemson Extension, wax begonias are an exception. They can handle full sun, and wax begonias with bronze foliage do better in sun than the green varieties. Well-drained, moist soil that has plenty of organic matter is a must for these plants as they are susceptible to root rot. 

Begonias can be started indoors from seed and then transplanted outdoors but they typically take several weeks. Small plants are readily available in the garden center.

When growing indoors as houseplants, use a quality potting mix. Use a container that has drainage holes. Do not allow water to stand in the saucer under the container.

When planting outside, wait until the danger of frost has passed. Work the soil so that it is well-drained. If needed, mix compost into the soil to help good drainage. Incorporate fertilizer into the soil when planting (see recommendation below). Plant in a location where they receive bright light but not direct sunlight, which can burn the foliage. Several plants placed together in a bed create a beautiful mass. Space plants about 12 inches apart to give them room to grow. In containers they can be planted closer together.

Water on a regular basis but don’t overwater. Begonias do not like wet feet. Avoid overhead watering and water at the plant's base, preferably early in the day. This helps avoid fungal leaf diseases. 

Fertilizing

• Minnesota Extension recommends incorporating a general-purpose fertilizer with equal amounts of nitrogen, phosphorous, and potassium into the soil at the time of planting. Follow label directions. 
• After planting, fertilize monthly using a fertilizer with a higher phosphorous than nitrogen content to promote new blooms. If growing for foliage only, continue using a balanced fertilizer. 

Controlling Pests, Diseases, and Other Problems

• Fungal diseases such as powdery mildew can occur when foliage remains damp for long periods. Good air circulation and avoiding overhead watering helps reduce those problems. If necessary, fungicides can be used for treatment. Follow label directions. 
• Thrips can transmit a virus that distorts leaves or causes black patches or wavy lines on leaves. Remove infected plants from the garden. While insecticidal soaps can be effective on many plants, begonias may be sensitive to them.

Tuberous begonias have a dormant phase so aren’t a good choice for a year-round houseplant (instead, try Rieger begonias, a cross between tuberous and wax) but tuberous begonias do produce tubers that can be dug at the end of the growing season and stored indoors in a cool, dry place until the next growing season. In fact, to enjoy this plant more than one season you will need to save the tubers as they will not survive winters in most places. Reduce watering and stop fertilizing at the end of August. Dig the tubers when the foliage starts to yellow. Cut the stems to about 2 to 4 inches and allow the tubers to dry indoors. 

Storing

When tubers from tuberous begonias are completely dry, place in a box filled with vermiculite or wood shavings and store inside in a cool, dry, dark place. 

• Get more bang for your buck by propagating cuttings. Simply cut about three inches off a branch, remove leaves from the bottom half of the cutting, and then place the cutting in water. When roots appear, plant the cutting in potting soil. 
• The American Begonia Society is a great source for more on begonias.