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 that are brightly colored in shades of green, red, silver, and even purple. Rex begonia is typically grown as an outdoor container plant or houseplant. It can be challenging to find just the right conditions for Rex begonia to display its best leaf color. Light is not usually the issue but temperature is key. Ideal daytime temperatures for this plant to thrive hover around 70 degrees Fahrenheit, nighttime temperatures around 60 degrees, 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:

• Use a porous potting mix in a relatively shallow pot.
• If planting outdoors, do so in May after frosts, but plant anytime indoors
• Feed the plant regularly.
• Keep the plant moist, but avoid over-watering.
• Provide the plant with plenty of bright indirect sun, but keep it out of direct sunlight.
• As a houseplant, rotate frequently to expose it to equal light on all sides.
• Pinch off blooms (which are insignificant) to maintain breathtaking 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. Their fine root systems prefer a well aerated peat-based potting soil in containers.

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, if misting leaves, ensure they don't stay too wet and encourage powdery mildew.

Temperature and Humidity

Rex begonias do best in moderate temperatures (60 to 70 degrees Fahrenheit) 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 foliage begonias prefer the same humid, gentle environment in which understory ferns thrive.

Fertilizer

Use liquid fertilizer weekly at quarter strength or half strength every two weeks. With a moderate growth rate, rex begonias may grow to less than 12 inches in a year.

Types of Rex Begonias

Begonia rex is the basis for many 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.

One interesting and beautiful begonia is B. masoniana, also known as the iron cross begonia. This beautiful plant was introduced to cultivation in 1952 and has puckered leaves with a dark cross in the middle. It's available in various colors.

Propagating Rex Begonias

The vast majority of begonias offered in the trade are hybrids so they cannot be accurately propagated from seed. Rhizomatous begonias such as the rex begonia can be easily propagated by rhizome division, layering, or leaf-tip cuttings. Here are steps for each method:

Propagating by division:

1. Divide rex begonias in the spring. Start by lifting the plant out of its pot.
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. Alternatively, you can put the stalk in a jar of water to encourage more growth from the roots before you pot it.
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 by layering:

1. Select a stem (with a leaf) that will easily bend down into the soil.
2. Carefully pin the leaf to the bedding mix using a U-shaped pin (a hairpin works well).
3. Make a couple of very tiny incisions in the leaf's veins so it can connect well with the soil and take care of the plant as usual.

Propagating by leaf cuttings:

1. Use a sharp, sanitized cutting tool to take off a leaf from the mother plant. The leaf should have a petiole, which is the stalk that attaches the leaf blade to the stem. Make the cut where the petiole meets the stem.
2. Gently trim the base of the petiole to clean up jagged edges.
3. Use a small paint brush to lightly paint the bottom of the petiole with rooting hormone to help the cutting sprout.
4. Use a clean stick to make a small hole in the soil for the petiole.
5. Insert the petiole stalk gently but directly into the hole in the soil. The leaf should not touch the dirt. Only the petiole stalk should be in the dirt.
6. Put the cutting in a location that is out of direct sunlight.
7. Keep the pot moist by making a mini-greenhouse. Put a plastic bag over the pot without touching the leaf.
8. Check every so often to see if the pot needs some watering.
9. Check for rooting in a few weeks after which you can remove the bag and bring the pot into a spot with more light.
   

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

The most common problem with rex begonias is wilting leaves. Besides a pest infestation, there may be other reasons why the leaves are wilting, including the following:

• The soil is too dry or too wet.
• The soil is not draining enough.
• The plant needs more light, but not intense light.
• The humidity levels are too low (but don't mist the plant because rex begonias do not like wet foliage).