How to Plant, Grow, and Care for Tuberous Begonias

Tuberous begonias are standouts among the group with decadent blooms in vibrant colors. Laden with flowers, they bloom from late spring through frost to brighten shady zones. Lightly fragrant, their full flowers delight the senses and draw pollinators.

With pendulous blooms and forms that trail, they’re ideal in hanging baskets, window boxes, and pots. Upright and standard selections make a striking border planting and filler feature in container arrangements. Distinct leaf colors and forms among varieties heighten visual interest and add surprise among shade-loving plants.

What Are Tuberous Begonias?

Tuberous begonias are a class of begonias native to tropical regions of South America and southern Africa. In frost-free USDA zones 9-11, they grow outside all year, and in cooler zones, they perform as annuals or overwinter by storing their tubers. They rose to popularity in the 1850s Victorian era for their large, luscious blooms and conservatory-worthy features.

When the floriferous tropicals begin blooming, they flower continuously for up to four months or until temperatures drop. They prefer climates with mild summers and suffer in high heat and intense sun. In southern climates, treat them as spring annuals for a scrumptious display and early pollinator attractor. 

Tuberous selections bridge the transition from winter to spring beautifully in the South and make a pleasing spring welcome. As temperatures rise, try placing them in the coolest shade spot available. In more northern climates, they flower with spring’s warmth and go through fall’s frost.

As with other begonias, their long bloom time and ability to flower in shade are unique qualities. Pair them with the dynamic foliage of caladiums, coleus, heuchera, hosta, and ferns. Impatiens and fuschia make lovely blooming counterparts.

Characteristics

The substantial blooms on tuberous varieties are single, double, or ruffled and often appear in pairs or clusters of three. From sunset apricot to blush pink, orange, red, white, and bicolors, the spectrum of hues brings a glow to shady garden spots or patio plantings. Many are picotee, where a delicate edge contrasts the main petal color. The fully-petaled flowers can reach six inches across and set them apart from other begonia classes. 

It’s their tuberous roots, though, that define the group. The American Begonia Society divides the genus into informal categories, including fibrous-rooted, rhizomatic, and tuberous. Due to 1800-plus species and hybrids, distinct grouping is a challenge. The tuberous class has fleshy, starchy, modified stems that form root-like structures. Roots and shoots grow from the same bud (like a potato). The Tuberosa Group is then further classed based on form (standard, trailing) and flower (rose, carnation, camellia).

Foliage is dynamic, often serrated and pointed, and in deep green to mahogany, depending on the variety. Some have striking leaf patterns, and forms vary between trailing, upright, and standard.

Tuberous begonias are monoecious, meaning each plant contains both male and female flowers. In clusters, the male is the prominent bloom, often larger and with more petals. The female flowers are smaller, and some gardeners remove the female blooms to direct energy to the larger male ones for display purposes.

Native Area

Parent tubers to today’s hybrids came from tropical Bolivia, Peru, and the lower Andes Mountains, as well as tropical zones in southern Africa. Their natural growing conditions experience mild temperatures, humidity, organically rich soils, and regular moisture accompanied by periods of drying out. They enter dormancy in cool months, where tubers store moisture and nutrients for the growing season.

Planting

Plant the tropical beauties in containers, hanging baskets, window boxes, and beds in bright shade, where you’ll enjoy their added color and texture. They’re available as potted specimens from nurseries in early spring and also grow from tubers.

Plan for air circulation between plants to prevent fungal issues, usually with a spacing of 8 to 12 inches, depending on the variety. Shelter them from winds, which can break stems, and provide protection from afternoon sun.

Transplanting and Growing in Containers

Tuberous begonias don’t withstand frost or cold temperatures. Place them outside in the spring after the final frost. Many of us treat them as annuals, but with fall’s approach, you may opt to overwinter them indoors by lifting and storing the tubers in a cool, dry space. This is an advantage of the tuberous root structures that they can store during dormancy. In subtropical climates, they thrive outside year-round. 

B. x tuberhybrida are prime for container culture. Hanging baskets offer good air circulation and show off trailing varieties. They perform well in pots one inch beyond the tuber on all sides. Too large a pot results in a soil vacuum that holds moisture for prolonged periods and can cause root problems.

Tubers

To grow tuberous begonias from tubers, start them indoors 8 to 10 weeks before the final frost. This gives them a headstart on development for earlier blooming. If planted later outdoors in northern climates, blooms won’t begin until late summer.

Place the tubers on a tray of moist potting media to break dormancy. A well-lit, warm location or a heat mat at 70-75°F (21-24°C) helps initiate budding. Press the tuber into the mix with the bud side facing up. Leave two inches of space around each tuber for root growth. Keep the media moist but not soggy as growth ensues. 

Transfer the tubers to pots when the growth is two or more inches tall. Harden them off outside after the final frost to gradually acclimate the tender tropicals to garden conditions.

How to Grow

The prolific bloomers need good airflow to thrive, as well as regular moisture and temperate conditions. While not overly high maintenance, tuberous begonias do need specific conditions to flourish. Lifting and storing the tubers adds to seasonal tasks but makes for repeat flowering and enjoyment.

Light

The Tuberosa Group shows the best vigor and flowering in bright, open shade. This may include the morning sun or dappled light. Even late sun won’t do harm, but direct afternoon exposure causes leaf scorch and burn.

Place them in a shaded spot, like under a tree canopy, for dappled light and protection from the midday sun. The species tolerate deeper shade but may show leggy, less robust growth and fewer flowers. They rely on light for the energy needed to bloom.

Water

The tropicals prefer evenly moist soils with consistent moisture throughout the growing season. Allow the soil to dry slightly between waterings, as the stems and tubers are water-filled stores. Water when the soil surface is dry to the depth of one-inch (about a knuckle deep).

Tuberous begonias are not particularly drought-tolerant and show stress during prolonged dry spells. Conversely, overwatering is a top cause of decline. Soggy conditions lead to pest vulnerability and diseases. Striking the balance of even moisture and watering when the soil surface feels dry is a good measure.

Avoid overhead watering to prevent foliar diseases or water in the morning so droplets dry during the day. A strong spray or driving rain can cause stem or blossom damage.

Keep an eye on containers as they dry out quickly in the summer heat. Depending on your climate, pot size, and potting media, they may need water daily.

Soil

Well-draining soils are essential to begonia health. Ideal soils are loamy with good organic matter. Amend poor soils like sand and clay with a generous compost layer when planting. Organic material adds nutrients and increases aeration and moisture retention. 

In containers, use a high-quality potting mix to promote aeration and drainage. These mixes contain lighter soils than those for in-ground plantings.

Temperature and Humidity

B. x tuberhybrida withers in hot conditions, and temperatures above 85°F (29°C) hinder growth. Grow them outside in spring when night-time temperatures are consistently above 50°F (10°C).

While they enjoy humid situations, a lack of air circulation causes dampness and fungal problems like powdery mildew and botrytis. Avoid crowding plants by ensuring proper spacing according to the selection. A natural breeze helps reduce stagnant air.

To increase humidity in the immediate area around your tuberous begonias, place pots on a pebble tray filled with water. Or, water the ground surrounding the plant during a regular session.

The water-filled stems are frost-sensitive and don’t withstand cold weather. Late spring frosts, chilly nights, or early fall cold snaps inhibit flowering. Plan to enjoy them through frost or bring them indoors in advance to their overwintering locale.

Fertilizing

The prolific bloomers are heavy feeders that benefit from a boost of nutrients and minerals to complete their life cycle in a single growing season. 

Apply an organic balanced fertilizer like 5-5-5, 8-8-8, or 10-10-10 when transplanting nursery specimens or when leafy growth emerges from tubers. A granular slow-release works well to distribute nutrients over time without overfeeding. Too much fertilizer, especially nitrogen, leads to weak, leggy stems.

A liquid feed during prime summertime flowering promotes larger and longer flowering. Use applications like fish emulsion, kelp, compost tea, or a formula specific to flowering plants. Higher phosphorus (P) is more beneficial than high nitrogen (N) in the NPK ratio for boosting blooms. Stop fertilizing in late summer as the tubers prepare to enter dormancy.

Maintenance

Pinch stems if they become leggy or as they develop from tubers to encourage side shoots and a bushy form. Pinch just above a leaf node to encourage side branching. Tuberous begonias don’t need deadheading, but you can remove faded blooms for a tidy look and to show off the current blossoms.

Storing and Overwintering

To store tubers for planting the next spring, lift them after a few light frosts in the fall, which causes the leaves to brown and drop. If in a pot, remove the soil mass and root ball. For in-ground plants, dig them and shake off excess soil. Inspect the tubers for health (no mushy or moldy spots) and trim any attached roots. 

Store the entire plant in a warm, dry area for several days to dry the tuber (if outside, bring it in at night to prevent freezing). Shake off excess soil and clip off any remaining roots or stems attached to the main tuber. Stems should come off easily when the plant is thoroughly dry.

Place the tubers in a tray or crate of dry material like sawdust, straw, coco coir, or vermiculite in a cool, dry space like a garage or basement. You can also put individual tubers in a paper bag and store them in a box.

Some gardeners have success overwintering tubers in their pots in a sheltered space (the same garage, basement, or unheated greenhouse). Wait until leaves die back after a few light frosts (before the first heavy frost) to move the container inside. After stems dry, cut them back to the base.

Propagation

Tuberous begonia propagation is easiest in the home garden through stem cuttings. They also grow from seed. Since many are hybrids and do not come true from seed, they’re best multiplied by taking cuttings in the spring.

Cuttings

Stem cuttings root in water or in soil media. To root them in water, follow the steps for taking cuttings and place them in a small, clear jar filled shallowly with water (multiple stems share a jar). Change the water daily or as it becomes murky until three to four-inch roots develop.

Growing From Seed

If you opt to try seeding, here are a few recommendations for the process:

Popular Varieties

Tuberose begonias bring an array of varieties to add light and intrigue with dynamic flowers and foliage.

‘NonstopⓇ Mocca Deep Orange’

The NonstopⓇ series brings continual blooms on robust forms. Fully double blooms in rich pigments are showstopping in the border or container arrangement. 

‘Mocca Deep Orange’ features red-orange petals against dark foliage. Leaves are velvety green and mahogany, with lighter venation, ridged edges, and distinctly pointed tips. Look to ‘NonstopⓇ Fire’ in gold-orange with red edging.

‘Picotee White-Pink’

In light pink and pure white with delicate deep pink edges, ‘Picotee White-Pink’ shows off true tuberous begonia style. Crisp double blooms are large on upright stems. 

The painterly petals have slight ruffles and a timeless appeal. The dark green and full foliage provides a showy backdrop to the bright blooms.

‘Splendide Apricot’

This cascading hanging basket variety has loads of four-inch double blooms that suspend from trailing stems. In apricot shades from soft pink to warm peach, the rose-form flowers hold their color through summer without fading.

In full flower, the rosettes almost obscure the glossy green leaves tinged with rose. Stems are reddish-orange to complement the pendulous petals.

Common Problems

Plenty of air circulation and avoiding overwatering help stave off problems. Occasional pests may visit, and fungal diseases can crop up.

Pests

The best way to control insects is to spot them early. You may see the insects themselves or notice their sticky waste on plants, yellowing leaves, or stunted growth.

Aphids are common sap-sucking insects usually treatable by non-chemical means. Often, they cause no damage, but severe infestations cause curled leaves and stunted growth. They’re also vectors for diseases and viruses. They leave behind a sticky honeydew, leading to black, sooty mold. 

Mealybugs are soft-bodied and look like tiny tufts of white cotton or dust on leaves and stems. In an infestation, you’ll see the insect accompanied by yellowing, wilting, stunted leaves, and decline. Like aphids, they feed on sap and lay eggs in cellular tissues. 

Early outbreaks are easy to control, but if not caught in time, mealybugs recur and are challenging to get rid of entirely. 

In pest outbreaks, spray leaves and stems with a stream of water to deter and knock insects off the plant. Do this in the morning so the leaves dry in the early sun. A horticultural soap or oil treats severe infestations but follow label directions, as these also affect beneficial insects. 

Slugs and snails may feed on fresh shoots. Hand-pick them early in the day or evening when they’re most active. If numbers increase, bait them with beer or soda traps by filling a shallow dish and placing it at soil level.

Diseases

As with pests, the best disease control is prevention through cultural conditions, especially through proper watering.

Botrytis is a fungal disease prevalent in high-humidity conditions with limited air circulation. Brown spots and “fluffy mold” appear on stems and leaves. Patches occur when spent blooms drop onto foliage in wet, humid conditions. Take care not to overwater or overfertilize, which weakens the plant.

Powdery mildew is one of the most common fungal problems. The pathogen Erysiphe appears as a grayish-white dust on leaves, buds, and stems. During severe infections, leaves turn yellow, distort, and drop. The fungus spreads quickly, and if left untreated, plants wither and eventually die. Fortunately, powdery mildew is treatable with early detection.

Frequently Asked Questions