Growing Begonia Rex Cultorum Group (Rex Begonia)

Pronunciation: beg-own'ee-uh

Aptly named "kings" of the Begonia tribe, these display gorgeous foliage in wildly variable patterns, colors (including metallic silver), and shapes (like the spiral 'Escargot'). Rex Begonias grow from a rhizome and are exacting in requirements but reward with stunning display. Popular as houseplants, ideal on shaded deck or patio, lighting up shady nooks. Flowers are insignificant—foliage is the main attraction.

Light/Watering

Proper light brings out best colors. Never direct sun; bright filtered light only. If light is one-directional, give quarter turn weekly. Allow soil surface to become almost dry between waterings during active growth; avoid overwatering. Use tepid water—cold water may shock plants. As days shorten and temperatures drop, plants may enter dormancy (growth stops, leaves may drop). Water sparingly until new leaves emerge in late winter. Rex Begonias require high humidity; dry air causes crisp leaf edges. Run a humidifier or place pots on gravel trays with water just below gravel tops—do NOT let pots sit in water.

Temperature

Hardy only in Zones 10–12; treated as annuals or houseplants elsewhere. Moderate daytime 65–70°F, nights around 60°F best. Sudden temperature changes may cause leaf drop.

Fertilizer/Soil and pH

Fertilize every two weeks from spring when new growth appears with balanced 15-30-15 fertilizer (e.g., All Bloom). Taper off in late summer/early fall, stop in winter, resume in spring. Light, free-draining soil high in organic matter preferred.

Pests/Diseases

Occasional mealybugs (cottony white bumps in leaf joints or on rhizome). Wipe with alcohol-dipped cotton swabs or spray insecticidal soap. Powdery mildew and botrytis may occur; good air circulation essential. Remove dead/diseased leaves and debris promptly. Systemic fungicide like Funginex if needed.

Companions

Lovely grouped inside or out with other plants preferring indirect light.

Repotting

Move into larger but shallow pots as needed, ideally in spring as new growth begins. Pinch back tips. If rhizome has grown over pot edge, cut it back to force new growth along rhizome.

Calendar of Care

• Early Spring: Resume feeding with 15-20-15 houseplant fertilizer. Repot if needed with light, free-draining, organic-rich mix. Shallow pots best. Pinch tips, trim rhizome if over pot edge. Move back to summer spots before sun intensifies.
• Mid-Spring: After frost danger, move outdoors to shady nook or sheltered patio. Acclimate slowly to avoid leaf drop.
• Summer: Continue fertilizing; monitor light to avoid burning tender leaves. Scout for pests and fungal problems.
• Fall: Move indoors as night temps fall below 60°F. Quarantine until certain no pests/diseases. Stop fertilizing.
• Early Winter: As days shorten and temps drop, plants may enter dormancy. Water sparingly until new growth in spring.