Growing Begonia Rex Cultorum Group (Rex Begonia)

Pronunciation: beg-own'ee-uh  

 

Aptly named, these "kings" of the Begonia tribe display gorgeous foliage in wildly variable patterns, colors (including metallic silver), and even shapes (such as the spiral variety called 'Escargot'). Rex Begonias grow from a modified stem structure called a rhizome and are rather exacting in their requirements, but will reward your efforts with a stunning display. Popular as houseplants, Rex Begonias are ideal on a shaded deck or patio, and can light up a shady nook with their striking colors. Flowers are generally insignificant as the brilliant foliage is the main attraction.

Light/Watering: Proper light levels will help bring out the best colors of Rex Begonias. Plants should never see direct sunlight and do well only in bright but filtered light. If light comes mainly from one direction, give each plant a quarter turn every week. The surface of the soil should be allowed to become almost dry between watering during active growth and you must be sure to avoid overwatering. Water with tepid water, not cold water, as it may shock the plants. As days shorten and temperatures drop, plants may enter dormancy—growth stops and leaves may drop. At this time, water only sparingly until new leaves emerge in late winter. Rex Begonias thrive only with high humidity. Dry air will cause the leaf edges to become crisp and dry and plants will languish. Run a humidifier, or simply place potted plants on trays filled with gravel and add water just below top of gravel—do NOT let pots sit in water at any time.

Temperature: Hardy only in zones 10 to 12, Rex Begonias are treated as annuals or as houseplants in colder areas. Moderate daytime temperatures of 65–70°F and nights around 60°F are best. Sudden temperature changes may cause leaves to drop.

Fertilizer/Soil and pH: Fertilize every two weeks beginning in spring when new growth appears with a balanced fertilizer with a 15-30-15 ratio, such as our All Bloom Fertilizer. Taper off feeding in late summer or early fall, and stop in winter, resuming again in spring. A light, free-draining soil high in organic matter is preferred.

Pests/Diseases: Occasionally mealy bugs may appear as cottony white bumps tucked into leaf joints or along the rhizome. Use cotton swabs dipped in rubbing alcohol to wipe off bugs, or spray with insecticidal soap. Two fungal diseases, powdery mildew and botrytis, may occur; good air circulation is essential. Remove dead or diseased leaves promptly as well as any debris on the surface of the planting mix. Good grooming goes far as a preventative, but a systemic fungicide like Funginex may be used if needed.

Companions: Lovely grouped inside or out with other plants that prefer indirect light.

Repotting: Move into larger but shallow pots as required, ideally in spring as new growth begins. Take this opportunity to pinch back tips. If the rhizome has grown over the pot edge, cut it back also, which will force new growth along the rhizome.

Calendar of Care - Rex Begonia

Early Spring: As new growth begins, resume feeding with a balanced houseplant fertilizer with a ratio of 15-20-15, such as our All Bloom Fertilizer. Repot if needed, using a light, free-draining soil mix rich in organic matter. These plants are shallow rooted, so shallow pots are best. Pinch tips back and trim off the rhizome if it has grown over the pot edge. If plants have been moved to a higher light area for the winter, move them back to their summer spots before the sun becomes too bright.

Mid-Spring: After the danger of frost has passed, plants may be moved outdoors to a shady nook or sheltered patio. Be sure to acclimate them slowly to the new conditions to avoid leaf-drop.

Summer: Continue fertilizing and monitor light levels to avoid burning tender leaves. Continue to scout for insect pests and fungal problems.

Fall: Move plants back into house or greenhouse as temperatures fall below 60°F at night. Quarantine plants until you are certain they harbor no insect pests or fungal diseases. Stop fertilizing.

Early Winter: As the days shorten and temperatures drop, plants may enter dormancy. If this happens, water only sparingly until new growth appears in spring.

For information on planting and care of annuals, click here.