How to Care for Rieger Begonias

Rieger begonia (Begonia x hiemalis) is a hybrid begonia variety characterized by broad, glossy leaves and showy blooms available in a range of colors. Growing up to 18 inches tall and 10 to 12 inches wide, the compact plant can be grown in a hanging basket or pot, or massed together as a bedding flower. Rieger begonias also work well as houseplants.

Rarely bothered by pests and diseases, Rieger begonias require minimal care to look their best.

Indoors, choose a location with bright, filtered sunlight, such as the light from an east-facing windowsill. In winter, move to the sunniest windowsill available to maximize light. Outdoors, plant in partial shade. Rieger begonias are hardy in U.S. Department of Agriculture plant hardiness zones 9 to 11.

Rieger begonias thrive in a temperature around 70 degrees Fahrenheit during the day and 50 degrees Fahrenheit at night.

Do not place in areas with hot or cold drafts. If frosts are predicted, move outdoor potted plants indoors until frosts pass.

If planting multiple Rieger begonies outdoors, provide at least 12 inches of space between plants. Pinch back long, leggy stems to maintain an appealing compact plant, and remove spent flowers to prolong flowering.

Increase humidity for indoor plants by placing the pot on a shallow tray with pebbles partially filled with water. Misting the surrounding air around the plant with water also increases humidity.

Plant Rieger begonias in soil that drains well. For potted plants, use a sterilized potting soil that contains equal parts organic matter, peat moss and sand or perlite. Water regularly to keep the soil evenly moist, allowing it to slightly dry out between waterings. Do not allow the soil to become flooded or waterlogged, and do not allow potted plants to sit in a saucer or tray with water.

After the first year, move potted plants to the next largest pot the following spring; Rieger begonias do not perform well when potbound. All pots must have a hole in the bottom for drainage.

Fertilize every two weeks during the growing season, from spring until the first frosts of fall, with a water soluble 15-30-15 fertilizer. Dilute 1/2 teaspoon of fertilizer into 1 gallon of water and apply mixture to the soil as if you were watering the plant. Keep out of reach of children.

Rieger begonias are usually not bothered by serious pest infestations, though common sap-sucking pests such as mealybugs (pale, slow-moving insects protected by a wax-like coating), spider mites (tiny, spider-like pests) and whiteflies (powdery, moth-like insects) can become a nuisance on indoor plants. All three can cause foliage damage. Both whiteflies and mealybugs can also excrete honeydew, a sticky substance that attracts black sooty mold.

A direct stream of water may be enough to dislodge pest colonies. Mites, mealybugs and whiteflies can be killed by spraying the plant with insecticidal soap. Mix 5 tablespoons of insecticidal soap per 1 gallon of water and spray the entire plant, thoroughly wetting all surfaces. Always follow label instructions exactly. Store unused insecticide in a secure location away from children and pets.

You can also remove mealybugs by hand by wiping the plant with a cotton swab dipped in rubbing alcohol.