Immense begonias, sought after for their massive, camellia-like blooms or strikingly large foliage, represent the grandest scale of the Begonia genus. This size is typically achieved by cultivating Tuberous Begonias (Begonia tuberhybrida) or certain rhizomatous varieties like Begonia ricinifolia ‘Immense’. Successful cultivation requires a specialized approach, providing the precise conditions and nutrients necessary to support robust growth. This guide details the foundational environmental setup, the routine of feeding and watering, and the seasonal care required to grow these magnificent specimens to their full potential.
Selecting the Site and Soil Preparation
Tuberous and immense-leaf begonias require a planting location that provides bright, filtered light to prevent leaf scorch. They thrive in conditions that mimic their natural understory habitat, receiving indirect sunlight or morning sun only, and must be shielded from intense afternoon heat. Larger pots directly correlate with the plant’s potential size, provided the soil volume is sufficient to support the extensive root system.
The soil mixture must be highly organic, well-aerated, and possess excellent drainage capabilities to prevent the tuber or rhizome from rotting. A common mix includes components like peat moss, perlite, and a small amount of sand, though many growers use soilless media. This blend ensures moisture retention without becoming waterlogged, a common hazard for begonias.
The growing medium should be slightly acidic, with a pH range between 5.5 and 6.5, which optimizes nutrient availability. When planting a dormant tuber, place it with the concave side facing upward, as this is where the growth shoots will emerge.
Routine Watering and Feeding Schedules
Consistent moisture is mandatory for immense begonias, but they are highly susceptible to rot if overwatered. Apply water directly to the soil at the base of the plant, avoiding the leaves, which can promote fungal diseases like powdery mildew. The soil should be allowed to dry out slightly between waterings, letting the top inch or two become dry to the touch before re-saturating the medium.
These large plants are heavy feeders, requiring nutrients to sustain abundant foliage and continuous production of massive blooms. A regular fertilization program is necessary for achieving immense size and flower quality. A diluted, balanced liquid fertilizer, such as a 20-10-20 N-P-K ratio, should be applied every one to two weeks.
During the initial growth phase, use a fertilizer slightly higher in nitrogen to promote lush, strong stems and leaves. Once the plant begins to set flower buds, shift to a formula higher in potassium to support the development of large blossoms. Fertilization should be reduced and stopped in late summer or early fall, signaling the plant to prepare for winter dormancy.
Seasonal Maintenance and Winter Storage
As the plants mature and produce heavy blooms, structural support is necessary to prevent the large, brittle stems from snapping. Staking with bamboo canes or using specialized grow cages provides the stability needed for upright varieties. Removing spent flowers (deadheading) is recommended, as it redirects the plant’s energy from seed production into creating new blossoms and foliage.
During the growing season, monitor for pests and diseases to keep the foliage healthy. Begonias are prone to fungal issues like powdery mildew and botrytis blight, often exacerbated by poor air circulation and high humidity. Pests such as mealybugs, aphids, and whiteflies can be managed with insecticidal soap or horticultural oil if detected early.
Tuberous Begonias are not hardy in cold climates and require careful preparation for overwintering. After the foliage naturally begins to yellow, or immediately after the first light frost, cut the stems back to about an inch above the tuber. The tubers are then carefully dug up and allowed to dry or “cure” in a cool, dry place for one to three weeks.
Once the tubers are cured, gently brush away any remaining soil and roots. Pack them in a dry, insulating medium like peat moss, vermiculite, or sawdust. The optimal storage temperature is a consistently cool environment between 40 and 50 degrees Fahrenheit, which keeps the tuber dormant without freezing. Storing the tubers ensures they remain viable for restarting indoors in late winter.