How to Grow and Care for Rex Begonias

Rex begonia, also commonly known as painted-leaf begonia or fancy-leaf begonia, is a semi-tropical perennial plant known for its large variegated leaves in brightly colored shades of green, red, silver, and even purple. Rex begonias are typically grown as an outdoor container plant or houseplant. The plants are round in shape and usually reach a height and diameter of eight to 12 inches.

It can be challenging to find just the right conditions for this type of begonia to display its best leaf color. Light is not usually the issue but temperature can be a challenge. Ideal daytime temperatures for this plant to thrive hover around 70°F, nighttime temperatures around 60°F, and indoors, a constant humidity level around 50 percent would suffice. Note that rex begonia is toxic to animals.

Rex Begonia Care

Here are the main care requirements for growing rex begonia:

• Light: Provide rex begonias with plenty of bright, indirect sun, but keep them out of direct sunlight.
• Water: Keep the plant moist, but avoid overwatering. Allow the soil to dry partially between waterings. 
• Temperature: Place the plant in an area with temperatures between 60°F and 70°F.
• Soil: Use a porous potting mix in a relatively shallow pot.
• Planting Time: If planting outdoors, do so in May after frosts have passed, but plant indoors anytime.
• Fertilizer: Feed the plant regularly.
• Rotation: As a houseplant, rotate frequently to expose it to equal light on all sides.
• Pruning: Pinch off blooms (which are insignificant) to maintain the impressive leaf displays.

Light

Rex begonias like bright, indirect light year-round. Because they are not aggressive bloomers, they can tolerate less light than other begonias and will thrive under fluorescent lights.

Soil

Airy, light, fast-draining soil is best for growing rex begonias in containers. Their fine root systems prefer a well aerated peat-based potting soil.

Water

Rex begonias require regular water, but don't overwater them. The soil should feel slightly, yet evenly moist. Allow the soil surface to become dry to the touch before watering. Don't let the soil become overly dry or the plant will begin to wither. The plants thrive on humidity but don’t let the leaves get wet, or you risk powdery mildew.

Temperature and Humidity

Rex begonias do best in moderate temperatures (60°F to 70°F) and moderately high humidity (around 50 percent). Growth will slow in freezing temperatures and some types of begonias go into a dormant period during the winter due to lack of light. As with other begonias, the rex and other begonias grown at home prefer the same humid, gentle environment in which understory ferns thrive.

Fertilizer

Use liquid fertilizer at half strength every two weeks during growing season.

Types of Rex Begonias

Begonia rex is the basis for hundreds of hybrids, and its forms are too numerous to count. The resulting hybrids are often known in the trade only by fancy trade names used to market the plants. As a result, you might find that the same crosses have different names in different garden centers.

Recent hybrid cultivars include:

• Begonia ‘Avatar’: This hybrid cultivar bred by Byron Martin has silvery pale green leaves touched with light purple and pink accents, and deep purple veining in its frilly-edged leaves.
• Begonia ‘China Curl’: The large tear-drop shaped leaves have spiral variegation patterns that alternate deep purple black and pale silver-green.
• Begonia ‘Curly Fireflush’: This richly-colored heirloom has pale yellow-green leaves edged with deep burgundy, with a pale lilac flush at the center. Originally called 'Bettina Rothschild' when introduced in 1866.
• Begonia ‘Emerald Wave’: This hybrid has dramatic spiraling leaves of emerald green and deep plum purple.
• Begonia ‘Fireworks’: A compact plant with a striking appearance, this hybrid has silver heart shaped leaves with dark red veining and pale plum edges.
• Begonia ‘Froggy’: The small white flowers are a delicate accent to the subtle yet stunning coloring of olive green leaves with black accents that invoke spiderwebs or stained glass.

Propagating Rex Begonias

Rex begonias can be propagated in water, by cuttings, or by division. Rhizomatous begonias such as the rex begonia can be easily propagated by rhizome division, layering, or leaf-tip cuttings. New growth takes about six weeks to emerge.

Here are steps for each method:

Propagating by division:

1. Lif the rex begonia out of its pot in the springtime. 
2. Gently prod the dirt with a clean pair of scissors between the stalks to begin encouraging the rhizomes to pull apart, trying to untangle them naturally and without too much force.
3. Replant the divided stalks with roots into their own pots.
4. Keep the repotted begonia and the potted divisions consistently moist (not soggy) and out of direct sunlight for the next couple of weeks to help them rebound from the stress.

Propagating in water:

1. Use a sharp, sanitized cutting tool to take off a leaf from the mother plant. Make the cut where the petiole (the stalk that attaches the leaf to the stem) meets the stem.
2. Gently trim the base of the petiole to clean up jagged edges. Use a small paintbrush to lightly add rooting hormone to the bottom of the petiole.
3. Use a stick to make a small hole in the soil for the petiole. Insert the petiole so that only the petiole, not the leaf, is in the soil.
4. Put the cutting in a location that is out of direct sunlight.
5. Put a plastic bag over the pot (without touching the leaf) to make a mini greenhouse and keep the soil moist. Check soil every few days; water if dry.
6. Check for rooting in six weeks, after which you can remove the bag and bring the pot into a spot with more light.

Propagating by leaf cuttings:

1. Lift the rex begonia out of its pot in the springtime. 
2. Gently prod the dirt between the stalks with a clean pair of pruners to begin encouraging the rhizomes to pull apart, trying to untangle them without too much force.
3. Replant the divided stalks with roots into their own pots.
4. Keep the repotted begonia and the potted divisions consistently moist (not soggy) and out of direct sunlight for the next couple of weeks to help them rebound from the stress.
   

Potting and Repotting

Rex begonias are rhizomatous plants that grow from a shallow and knobby rhizome. As such, they do best in large, relatively shallow pots where the rhizome has room to spread. If the rhizome still has room to grow in its pot, the begonia should be considered happily potted.

When the rhizome begins to butt up against the sides of the pot, however, it's time to repot into a fresh pot with fresh soil. Divide the rhizome when repotting to increase your plant stock. As with all begonias, don't soak the soil of newly potted plants, but do keep it lightly moist and warm.

Common Pests and Diseases

Mealybugs can be an issue for rex begonia plants. To prevent the pests, keep the plant well-trimmed and remove dead leaves from the surface of the planting mix.

Rex begonias are often troubled by powdery mildew and botrytis fungal disease. A systemic fungicide can help with both issues. Remove dead leaves promptly and provide good air circulation.

Common Problems With Rex Begonias

Wilting Leaves or Leaf Loss

Wilting leaves or leaf loss on a rex begonia be caused pests, soil that is too wet or too dry, too little light, and low humidity. Assess the plant’s conditions and adjust accordingly to better meet its preferred conditions.

Soft Leaves

If rex begonia leaves lack substance or feel mushy or soft, the issue may be overwatering or underwatering. It's tricky to get this balance right, but a good rule of thumb is to check the top inch of soil before watering, and only water when it feels dry. Water deeply and let excess water drain out. Water shouldn’t stand on the surface of the soil; if it is, repotting and replacing the soil may help.