How to Grow Begonias Indoors and Outside, According to Gardening Experts

Begonias are beautiful tropical plants perfect for growing in shady or partial-sun areas. Many gardeners love begonias for their gorgeous, brightly colored blossoms in hues including white, yellow, orange, pink, and red. When they're not in bloom, their glossy foliage takes center stage.

Begonia is one of the largest genera of flowering plants, with nearly 2,000 species and hybrids (there is even a variety named after Martha!). In warmer climates, these plants can be grown as perennials, coming back bigger and better every year. In colder climates, begonias are typically grown as annuals or overwintered indoors as a houseplant.

Because begonias are typically understory plants, they prefer partial sun to full shade and moist soil. Ahead, we spoke to horticulture experts for tips on growing begonias, including how to prune and propagate these popular plants.

Types of Begonias

The type of begonia you have will dictate its care needs. These are the most common types of begonias you're likely to see at nurseries.

Cane: Cane begonias have many tall, woody-looking stems. They have wing-shaped leaves that are pointy and can be shiny or hairy. Occasionally, they are called "angel wing begonias" for their leaf shape. Many produce clusters of flowers in hues of pink, red, and white, blooming from spring to fall. 

Hardy: This classification of begonias is lesser known. As the name implies, hardy begonias can handle cold weather. These plants do best in moist soil and prefer partial shade. 

Rhizomatous: These plants grow from a rhizome, a thick stem below the soil that usually grows horizontally with sprouts emerging. Many begonia species are rhizomatous, flowering in the winter as they can manage with less light than other begonia species.

Tuberous: These begonias grow from tubers. Tuberous begonias range in style as some have multiple stems, often with the roots and shoots emerging from the same buds. Many produce large flowers that gardeners prize.

How to Care for Begonias

How you care for begonias depends largely on the type you're growing, but generally, these plants need partial sunlight, evenly moist soil, and above-average humidity.  

Sunlight

Each type of begonia will have its own sunlight needs. Some begonias do best in partial shade, while others thrive in full sun. That said, because begonias are understory plants in their native climate, most varieties prefer some shade. When choosing your variety, check how much light it will need and plant accordingly. 

Soil

Begonias need a well-draining, airy, soilless potting mix that is not too peat-heavy, says Christina VanWyk, president of the Delaware Valley Branch of the American Begonia Society. "Begonias prefer a neutral to slightly alkaline pH." A soil test will tell you how basic or acidic your soil is and what amendments it needs.

Water

Watering begonias properly is key to their success. "Begonias prefer evenly moist soil but do not like to sit in water," says Kelly Funk, president of Jackson and Perkins. "Allow the top inch of soil to dry out before watering again."

One of the best ways to know if begonias need water is to check the soil. "To check when to water begonias planted in the ground, simply insert your finger into the top inch of soil," says Autumn Hilliard-Knapp, horticulturist at My Perfect Plants Nursery. "If it's dry, it's probably time to water your plants." In hotter climates, be aware you may need to water more frequently. 

Temperature and Humidity

Because these plants grow in tropical and subtropical environments, begonias thrive in warm, humid regions. These plants do best in warm and hot climates where temperatures are consistently above 60 degrees Fahrenheit. In USDA Zones 5 and colder, treat begonias as an annual.

Fertilizer

Fertilize begonias during spring and summer. "When begonias are actively growing, you can fertilize once a month with bone meal, which offers a higher phosphorus content," says Jen McDonald, certified organic garden specialist and co-founder of Garden Girls. "While nitrogen promotes leafy green growth and contributes to strong plant systems, phosphorus is responsible for more blooms." That said, avoid over-fertilizing your begonias as this can lead to root burn, adds Funk.

Growing Begonias Indoors

Most houseplant begonias are rhizomatous varieties, such as the popular rex begonia. Begonias grown indoors need similar care as they do when grown outside. Ensure the soil stays moist but not waterlogged. Containers typically dry out faster, so you may find that your houseplant begonias need more frequent watering than in-ground types. Place your indoor begonias near an eastern window that receives bright morning light, but away from direct sunlight.

Pruning & Deadheading

Many plants need to be pruned to promote growth and maintain their appearance. "All varieties of begonias require grooming and pruning for a full, compact plant," says VanWyk. To prune begonias, simply cut off a few stems above a leaf node, being care not to remove more than one-third of the plant at one time.

Deadheading begonias is important for optimal growth and plant development. "It reminds the plant to send energy to new growth and will reward you with increased blooms and a bushier, healthier plant," says McDonald. "It also helps in preventing fungal diseases, as you are removing spent blooms that are likely to rot if left untouched." To deadhead begonias, cut or pinch off dead or dying blooms.

Propagating

Begonias can be propagated through leaf cuttings. "When choosing a leaf, one should look for a healthy, young but fully grown leaf," says VanWyk. "The easiest and most successful part of the leaf to propagate is where the petiole attaches to the leaf." The petiole is where the base or stalk of the leaf connects to the stem.

1. Using sharp, sterile scissors, cut a petiole about 1 inch below the leaf.
2. Fill a small container with moist, well-draining soil.
3. Place the petiole in the soil. Avoid letting the leaf touch the soil. 
4. Place the leaf-cutting in a warm area with bright, indirect light.
5. Optional: Boost humidity by placing a plastic container or bag over the cutting.
6. In a few weeks, small leaves should start appearing.
   

Potting and Repotting Begonias

Wait to repot your begonia until the current pot is filled with roots. You'll know it's time to repot this plant if you pull it out of its pot and the potting soil stays together around the roots. Choose a container with a drainage hole that is only slightly bigger (1 to 2 inches) than the current container.

1. Gently remove the plant from its container. Tease and loosen the roots.
2. Cover the bottom of the new container with well-draining potting mix.
3. Place the plant in the container and backfill with soil.
4. Water well and place the plant in a warm area with bright, indirect light.

Common Problems

Like most garden plants, begonias have their foes—but with knowledge and care, pests and diseases shouldn't be too much of a problem.

Powdery Mildew 

A fungal disease, powdery mildew, can plague many outdoor plants, including begonias. Spores are the culprit, spreading by water, wind, or insects. Powdery mildew can be prevented with ample air circulation. "To prevent the occurrence of powdery mildew on begonias, it is important to promote good air circulation around the plants," says Hilliard-Knapp. "This can be achieved by ensuring proper spacing and avoiding overcrowding." 

The way you water your begonias can also create a haven for powdery mildew to take over. "Water the plants at the base rather than overhead, as wet foliage can create an environment for the growth of the fungus that causes powdery mildew," says Hilliard-Knapp. If your begonias often get powdery mildew, consider applying a preventive treatment to help minimize the disease. "Use a fungicide as a preventive measure if powdery mildew has been a problem in the past," says Funk.

Root Rot  

Root rot is a fungal disease that typically results from overwatering. "Begonias are very susceptible to root and stem rot," says VanWyk. While root rot is often associated with container plants, it can happen in the ground, too. Root rot is preventable—don't overwater your begonias, and avoid soggy soil—especially for begonias planted in containers.

Mealybugs

Mealybugs are a common pest that can affect begonias. "The best way to prevent mealybugs from entering your collection is to isolate any new plants you bring home," says VanWyk. It's not always easy to tell if a plant has mealybugs, which is why it's crucial that plants are separated before incorporating them into your garden. "New plants should be isolated for at least three months, which is the life cycle of the mealybug," she adds.

If you find mealybugs on your begonias, there are ways to treat them. Dip a cotton swab into 70 percent rubbing alcohol and dab it directly onto the mealybug to kill it, then remove it from the leaf, says VanWyk. Another option for managing mealybugs is to introduce other insects to eliminate them. "A preventative integrated pest management (IPM) rotation of beneficial insects can also be crucial in eliminating harmful pests we may have missed when inspecting the new plants we have brought home," says VanWyk.

Spider Mites

Spider mites are another common pest that can harm your begonias. Checking the leaves often is key to detecting them. "Spider mites can be controlled with regular inspection of leaves," says McDonald. "They often prefer to hide in masses on the undersides of tender leaves."

Once you find spider mites, there are a few ways to get rid of them. One is spraying the leaves with a garden hose in the morning, so there's enough time for them to dry by evening. "Gently spray the begonia with water, paying close attention to the undersides of leaves where the mites often reside," says Hilliard-Knapp. 

Another option is to remove the leaves with a significant spider mite population. "By removing the infested foliage, you can help prevent the mites from spreading to other parts of the plant," she says. If you choose to remove leaves, remember to never remove more than one-third of a plant at one time, or you’ll send it into shock, McDonald warns.