Rex begonia, the king begonia, is a species of flowering plant in the family Begoniaceae. Rex begonias are rhizomatous, growing from a thick, fleshy rhizome with shallow roots. They can be difficult to grow because they generally thrive in humid environments with high light levels but can resent the same conditions at other times. However, with proper care, they are rewarding specimens. Rex begonias are most commonly grown in hanging baskets or in containers where they can be exposed to higher light levels than those reached by their leaves. There are many different cultivated varieties, the most important being Rex Giant, Rex Superba, Rex Alba, and Rex Secundiflora. Rex begonias may be grown with other flowering plants, but they are particularly useful for small areas. They are of particular value as cut flowers. The large white flowers appear in clusters, these lasting well as dried specimens. The variety ‘Rex’ is resistant to mealy bugs and other pests and has longer blooms than ‘Superba’. The flowers are slightly fragrant, but not particularly attractive to insects or pollinators.
Rex Begonia Types
Rex begonias are often simply called Rex begonias, but there is a lot of confusion with the names of different varieties. Here are the types of rex begonias.
- Ballet Begonia: Ballet Rex is best suited to low-light situations and does not do well in full sun. The leaves have fine, ovate leaflets, often with a wavy margin. The flowers are small, white, and fragrant. They bloom into early autumn.
- Flamenco Begonia: Flamenco Begonia is best suited to cooler temperatures. The leaves have dense, deeply cut, ovate leaflets with a wavy margin. The flowers are white and fragrant.
- Little Pearl Begonia: Little Pearl Begonia are best suited to low light situations, including nighttime temperatures as cold as -10°F (-23°C). They have densely cut leaves with a sharp-toothed petiole, forming a small rosette. The flowers are small and fragrant. They bloom into early autumn.
- Rex ‘Superba’ Begonia: Rex ‘Superba’ Begonia has a large rosette of palmately lobed leaves. The leaves are golden-green with a conspicuous silver line running parallel to the leaf margin. The flowers are white and fragrant; blooming from mid-spring to late summer into early autumn. The flowers last well as dried specimens when harvested in the fully open stage. While ‘Superba’ is not resistant to mealy bugs, it does have longer blooms than the variety ‘Rex’.
- White Supreme Begonia: The variety is a relatively compact plant, reaching an average height of 12 – 16 inches (30–40 cm). The leaves are thick, leathery leaves edged with a pronounced silver line running parallel to the leaf margin. The petiole is swollen and spiny, forming several lobes which make the leaf look much like a plume of feathers on a swan. The flowers are white, fragrant, and slightly ruffled.
- Blue Supreme Begonia: Its large plumes of white flowers produce a striking effect in any small space. The leaves are large, and ovate but shallowly lobed on the margins, with purple spots creating a very eye-catching appearance. This plant is especially strong in bright light but does well in partial shade as well.
- Silver Limbo Begonia: Silver Limbo Rex is best suited to cooler temperatures. The leaves are deeply cut, ovate, and quite leathery in appearance. The flowers are white and fragrant, blooming into early autumn.
- Rex Secundiflora Begonia: Rex Secundiflora has a single spike of large, showy silvery-blue flowers. It is less vigorous than most begonias and needs even shade to thrive. The leaves have wide ovate blades with deep cut lobes, giving the plant a somewhat feathery appearance. The short flower stems produce long white fading blooms that continue to bloom for several weeks after being cut from the plant.
Here are tips on rex begonia care.
Escargot Begonia Growing Conditions
Rex Begonia Escargot is a relatively new and very large flowered Begonia. The flowers are long-lasting as cut flowers, up to ten days, and they are big and showy. They take just a little longer than the Superba variety to mature into an established plant. The plant grows quickly, with a large rosette of leaves often 10 inches or more in diameter or more. This variety requires average watering but be sure it drains well before drying, the leaves must have good drainage for this plant to perform at its best.
- Temperature: Rex begonias thrive best if kept between 65 and 78 degrees Fahrenheit (18-21 degrees Celsius). They grow outside in some areas of the US. A cold greenhouse should be kept at a minimum of 55 degrees Fahrenheit (12.8 Celsius) and night temperatures may be as cool as 40 degrees Fahrenheit (-4 Celsius). Keep them warm in the winter, but do not allow water to sit on their leaves. This is because the begonia will lose its glossy appearance and you will not be able to see the bright colors of the plants.
- Watering: Begonias need a lot of water. They can tolerate drought conditions provided they are watered well before dryness sets in. Keep their soil moist, but avoid wetting the leaves as they tend to rot easily if they get wet. The roots produce a substance called glucomannan which is found in many types of leafy greens, among others in spinach and Swiss chard, that help prevent rot by absorbing excess moisture. Use about one inch (2.5 cm) per week for Begonia Escargot.
- Light: Rex begonias grow best in bright shade, but the leaves can burn if exposed to the sun. Begonias grow best with two to four hours of direct sunlight a day. Begonia Escargot prefers full shade to part sun and any hot direct sun will burn their leaves. On the other hand, do not let them sit in a dark corner where light cannot reach them at all. The leaves need some light for photosynthesis and will eventually start to wither away from the lack of sufficient light.
- Humidity: Begonias like moderate humidity (50-60%) with relatively dry air. This includes the leaves and the pots in which they are growing. If the humidity is too high, the leaves may become sticky and rot. Keep them moist by letting the potting mixture dry a bit before watering it again. A little moisture will evaporate quickly with the movement of air and a lot will condense on dry surfaces when slightly humid conditions persist so if you regularly water your plant, you may want to remove excess water from its leaves by misting or spraying with a stream of air before watering again to reduce condensation. Low humidity can cause wilting of leaves and in extreme cases death.
- Soils: Begonias need a rich, free-draining potting mixture for growth. They can grow in a variety of soils, including those that contain large amounts of sand and even small amounts of cinders. Most rex begonia growers use a standard peat-based potting mix that is amended with extra perlite or vermiculite to increase airflow and trainability. A mix with a pH of 5.5-6 will work well as the tap water used in most homes is close to this level. If you have very alkaline water, you may want to add some sulfur to the soil when potting up your plants to lower the pH. Avoid very acidic soils as these can cause root and leaf damage.
How to Grow Rex Begonia
Rex begonias are grown from seed and require about four months to reach maturity before being ready for flowering. They thrive in full sun and well-drained soil that is kept moist during the growing season (spring through autumn). Allow the soil to dry out a little between waterings. While most of the elements of your garden want moisture, harvest all flowers immediately after flowering and before they wilt. Lift the entire plant from its pot and cut off any dead flower stems with a sharp pair of scissors if you are going to leave them on your plant. You can grow begonias as cut flowers. If you are growing them from seed, allow the soil to dry out and then sow the seed in a nursery pot filled with potting soil. Water the seeds quite frequently while they grow, especially if it is warm outside. When they are large enough to handle and they are ready to be potted up, prepare a growing bed by digging over a vacant area in your garden. Begonias do not transplant well but can be propagated by dividing their roots every spring. Prepare to plant holes that are as deep as possible. The roots should be easily visible after you cut them off from the parent plant while they are still relatively small.
Pests and Diseases
Identifying pests and diseases on begonias is not simply because they are very difficult to distinguish from one another. Here are some pests that could affect your begonias.
- Broad Mite: Mites are among the most common pests and they are present on most begonias. The mite most often seen on begonias is the broad mite, greenhouse mite, or two-spotted spider mite. They suck the juices from the leaves of your plants eating holes through them and causing the leaf to appear silvery if you view it from above. If the area is large, spraying or dipping in soapy water will deter them for a short time. Another method is to crush the pest between your thumb and forefinger and then pull out the legs by their base. Use a cotton swab dipped in rubbing alcohol to remove their exoskeletons from the affected leaf.
- Lace Bugs: Lace bugs attack and skeletonizes your foliage before moving on to other plants in your garden. They eat the undersides of the leaves and their presence is usually indicated by webs they create while they wait for the foliage to appear. While these bugs are not serious pests, they can cause some leaf loss. To deter them from attacking your plants, remove as much of the webbing as possible with a paintbrush or soft cloth wet with soapy water. Spray plants regularly with insecticide and check for eggs on the undersides of leaves. Remove eggs and adults when you find them.
- Nematodes: Nematodes are microscopic worm-like animals that attack roots and can kill the plant. They cause plants to wilt and die. Remove most nematode infestations by digging up and destroying the infected plants. Avoid using heavy chemical fertilizers on begonia beds as these may increase the nematode population in the soil.
- Scale Insects: Scale insects are small, immobile insects that feed on plant sap with their piercing-sucking mouthparts that are found on stems, leaves, and fruits of many species of plants. They often start as a small red or white bump, which may swell and become painful. Scale insects are usually small, less than 2 mm long, but can be larger. When you see it, remove these insects by hand, dipping them in soapy water or rubbing them off with a cotton swab dipped in rubbing alcohol. Removing these insects from the plant is usually a job for the entire family.
Some diseases that could affect your begonias are bacterial leaf spots, powdery mildew, botrytis, Pythium root rot, and Rhizoctonia crown rot.
- Bacterial Leaf Spot: Bacterial leaf spot appears as small, purple spots surrounded by a yellow halo. It is common on the lower leaves of your plants and spreads rapidly as it is carried by water splashed from the leaves of one plant to another.
- Powdery Mildew: Powdery mildew is not a true fungus but a parasitic plant that covers the begonia’s leaves with a powdery white coating. While this disease won’t kill begonias, it may reduce the vigor of their growth, especially if they are already stressed. Prevent infections by removing dead or yellowed foliage, pruning off any affected stems, and giving them plenty of room to grow so they can receive adequate air circulation.
- Botrytis: Botrytis is a fungus that causes brown, beige, or grey spots on leaves. These spots will eventually grow into lesions and appear wet. Remove and destroy affected plants to avoid spreading the disease to other begonias.
- Pythium Root Rot: Root rot is not a specific disease but rather any number of root diseases that attack begonias from the roots up. Symptoms of root rot include wilting, reddish stems, yellowing leaves, and fungus growth in the soil around the crown area of the plant. Avoid these problems by providing your plants with plenty of drainages and keeping them well-ventilated.
- Rhizoctonia Crown Rot: Rhizoctonia crown rot usually appears on begonias that are kept too wet. This disease is identified by leaves and stems that turn yellow, brown, or black, and collapse after a small area around the crown becomes brown and mushy. Avoid this problem by allowing the soil to dry out between waterings and improve drainage. Some hosts of the disease can be eliminated by adding dolomitic limestone to your soil before planting.
Fertilizing the Plant
Be sure to feed your begonias every two weeks during the growing season. Select a balanced fertilizer specifically formulated for flowering plants and apply a ratio of one teaspoon of soluble fertilizer in one gallon of water. Apply the solution to all the plant’s foliage by watering it into the soil around and under each plant. The flowers should be fertilized every week with about one-quarter strength, but you should never fertilize too much or too frequently on begonias because this will lead to weak stems. Once mid-autumn arrives fertilizing should be discontinued. Like all flowering plants, begonias need calcium added to their growing medium with a 1:1 ratio of calcium nitrate (Ca(NO3)2) and dolomite lime (CaO). This can be done using a 1:1 ratio of each when planting the seeds, or by applying two tablespoons of lime per plant per week. If you are using a prepared potting mix, add 1/2 teaspoon of dolomite lime to the soil in each 3-inch diameter pot and mix in thoroughly.
Propagation of the Rex Begonia Plant
When you want to propagate escargot rex begonia, choose a stem that is close to its leaf node and cut it just above the node. Remove the leaves from the seedling to expose the roots of the new plant. Use a sharp pair of scissors or pruning shears because it is difficult to remove all dead leaf matter at once. Place your young begonia in a separate pot and repot it into its container, keeping moist after transplanting but with very little water placed in until the roots are well established. You can propagate your begonia by dividing the roots, which should be done whenever the plant is at least two years of age. Dig up the entire plant and divide it down to its root ball. All begonias can be grown from seed, but the seeds should be sown in a sterile growing medium. Leave enough soil attached to the roots so that they will not dry out while you are working on them. Remove any dead foliage around the seed and cover the pot with a plastic bag. Keep the soil moist but do not overwater. After 10 to 12 days remove the bag and begin to water well until germination begins, then gradually reduce watering. About 26–30 days after sowing, remove any remaining partially formed green leafy growth and sow your seeds. Allow the seeds to germinate in a separate tray or pot before transplanting them into their growing media.
Care of the Rex Begonia Flowers
Keep the begonia in a place where it will receive full sunlight, but not direct sunlight. This plant needs warmth to grow properly, so keep it away from heaters and hot lights. Place the begonia in a 65-to-70-degree area that is bright and warm with no drafty areas. Rex begonia flower buds are poisonous to cats and dogs, but almost any animal that can eat them without getting sick will be fine. To maintain their health and vigor, keep them in pots with a planting pad or under a grow light that exposes the roots to more sunlight than the top leaves. Different rex begonia varieties require different amounts of light. You should water them regularly to keep the soil moist but not overwatered. The begonia plants that you keep indoors will need to be watered more frequently than those you keep outdoors, especially during spring and summer. To avoid overwatering, water plants in the morning so any standing water will dry out within 4 hours. Do not soak them in water as this can cause root rot and disease.
The Rex Begonia plant is a beautiful addition to your garden or greenhouse, and when properly cared for it will last for many years and provide you with a beautiful flower. This flower is not as hardy as other begonias, but you can keep it warm in your home and greenhouse by using heating equipment. These begonia flowers are delicate, so you must be careful how you handle them. Try to keep it safe from anything that could harm it, such as frost or over-watering. It is not a very hardy plant and should not be left outside during the winter months.