Begonias are highly sought-after ornamental plants, prized for their diverse foliage, striking colors, and continuous blooming capacity. Their wide range of species and cultivars includes fibrous, rhizomatous, and tuberous types, offering flexibility in selection and propagation. Whether starting with a dormant tuber, taking a cutting from an existing plant, or attempting seed starting, begonias offer multiple avenues for cultivation.
Waking Up Dormant Tubers
Tuberous begonias enter dormancy, usually over winter, and require specific conditions to prompt new growth in the spring. To initiate this process indoors, place the tubers in a shallow tray or pot eight to twelve weeks before the last expected frost date. Use a well-draining, slightly moist substrate such as peat moss, coco coir, or a soilless mix.
Proper orientation is important for successful sprouting. Begonia tubers have a concave, bowl-like side, which contains the growth points. This indented side should face upward. The tuber should be pressed lightly onto the surface of the medium, or barely covered to a maximum depth of 2 centimeters, ensuring the top remains exposed.
The environment must be warm to encourage sprouting. Maintain a consistent temperature between 70 and 75 degrees Fahrenheit for rapid growth initiation. The medium should be kept just barely moist, as too much water can cause the tuber to rot. Once the first pink shoots appear, move the plant into brighter, indirect light to support foliage development.
Propagating New Plants from Cuttings
Propagation by cuttings creates genetic clones, maintaining specific traits of a desired variety. The technique depends on the begonia’s root structure: stem cuttings are used for cane and fibrous types, while leaf cuttings are used for rhizomatous varieties like Rex begonias. Stem cuttings should be taken from healthy, non-flowering shoots, ideally three to five inches long with at least one node.
For cane and fibrous types, remove the lower leaves. The cutting can be dipped in a rooting hormone to enhance root formation. These stem sections root reliably in a sterile medium composed of perlite, vermiculite, or a light sand and peat mix, which provides aeration and moisture retention. Maintaining high ambient humidity, often achieved with a clear dome or plastic bag, prevents desiccation while roots are forming.
Rhizomatous begonias are propagated using a leaf-section method. Select a mature, healthy leaf and score or cut its primary veins. The entire leaf or sections of it are then laid flat, vein side down, onto a moist rooting medium. New plantlets will form where the cut veins contact the substrate. All cuttings should be placed in a location with bright, indirect light to provide the energy needed for root development.
Germinating Begonias from Seed
Starting begonias from seed is the most technically demanding method due to the minute size of the seeds and their specific environmental needs. Begonia seeds are dust-like, requiring careful handling and precise sowing techniques. Since these seeds require light to trigger germination, they must be surface-sown and never covered with the growing medium.
Use a sterile, fine-textured starting mix, such as screened peat or a peat-vermiculite blend, to prevent “damping off.” After moistening the medium, gently sprinkle the seeds across the surface. Cover the container with a clear lid or plastic wrap to maintain near-100 percent humidity, which is necessary because the tiny seeds can dry out quickly.
Consistent warmth and light are required for seed starting. A temperature range of 70 to 75 degrees Fahrenheit promotes the fastest germination. Since natural light is often insufficient, place the trays under grow lights for 14 to 16 hours a day. Seedlings develop very slowly, often taking several weeks to germinate and many months to reach a transplantable size.
Transitioning Started Plants to Containers
Once begonia plants have developed a robust root system, they must be moved into individual containers for continued growth. Plants started indoors benefit from hardening off before being moved outside permanently. This involves gradually exposing them to outdoor conditions, including cooler temperatures, wind, and direct sunlight, over one to two weeks.
When transplanting, select a well-draining potting mix that is slightly acidic (pH 5.5 to 6.0), often a peat-based formula amended with perlite or orchid bark. A highly porous mix prevents waterlogging, which can cause stem or root rot. The new pot should only be slightly larger than the previous one, as begonias prefer to be somewhat root-bound, and large containers can contribute to overwatering issues.
For tubers and seedlings, plant them at the same depth they were previously growing. Rooted cuttings should be positioned so the former soil line is maintained in the new container. After transplanting, water the plants thoroughly and place them in a location with bright, indirect light, allowing them time to acclimate before initiating a regular feeding schedule.