The Rex Begonia, known for its stunning, highly decorative foliage, is typically grown in a well-draining soil mix. This plant is prized for the complex colors and textures of its leaves rather than its flowers, making it a popular indoor ornamental. While it can survive long-term in a semi-hydroponic setup, water is primarily used as a method for propagation. Water provides a clean, visible medium to encourage new root growth from a cutting.
Preparing Cuttings for Water Propagation
Rex Begonias can be propagated using either a stem cutting or a leaf cutting in a water medium. For a traditional stem cutting, select a healthy piece of the rhizome or stem with a leaf or two attached, using a clean, sterilized blade. The more common method utilizes a single leaf, where the entire leaf blade or sections of it can be used to generate a new plant.
For leaf propagation, take a whole, mature leaf and make shallow slices across several of the largest veins on the underside. These small wounds are the sites from which new roots and a plantlet will emerge. Alternatively, cut the leaf into wedge-shaped sections, ensuring each section contains a piece of a major vein where growth will occur.
Before placing the cutting into water, allow the cut end to dry out for a few hours. This brief period encourages the formation of a protective layer, known as callusing, which helps seal the wound. Callusing reduces the chance of the cutting absorbing too much water and rotting once submerged. The cutting is then ready to be placed in a glass vessel, with only the cut surface or the petiole submerged.
Optimizing the Rooting Environment
Once cuttings are placed in water, maintaining the correct environment promotes healthy root development. Rex Begonias prefer bright, indirect light, which is also the ideal condition for water propagation. Direct sunlight can overheat the water, causing thermal shock and creating an environment where algae and bacteria proliferate rapidly, which is detrimental to the developing roots.
The ideal water temperature for rooting is consistently warm, generally above 68°F (20°C), which stimulates cellular activity and root initiation. Stable temperatures are preferable, so avoid placing the vessel near drafts or air conditioning vents that cause fluctuations. Tap water often contains chlorine or chloramine, which can be harsh on new growth. Allowing tap water to sit out overnight or using filtered or distilled water is beneficial.
The most important maintenance step is regularly changing the water, ideally once a week. Changing the water removes decaying material and bacterial buildup, and it replenishes the dissolved oxygen content. Roots require oxygen for cellular respiration, and stagnant water quickly becomes depleted of this gas, which can lead to the cutting rotting before roots can form. Root development typically begins within two to four weeks, appearing as fine, white filaments emerging from the cut surface.
Successfully Transitioning to Soil
The roots that form in water, known as water roots, are structurally different from soil roots; they are more fragile and accustomed to a constant supply of moisture. The cutting is ready to be transferred once these new roots are about one to two inches long, providing enough surface area for nutrient and water uptake. Waiting too long allows the water roots to become overly adapted and makes the transition more difficult.
For potting, a small container is recommended because a large pot holds excess soil that can remain wet for too long, risking root rot. The soil mix should be light and well-draining, such as a blend of standard potting mix amended with perlite or peat moss. This airy composition mimics the high-moisture, high-oxygen environment the water roots are used to, easing the shock of the transition.
After gently placing the rooted cutting into the soil, immediately water it thoroughly. Then, place it in an environment with high humidity, which minimizes transpiration stress while the fragile roots adjust. High humidity can be achieved by covering the pot with a clear plastic dome or bag. Over the next few weeks, gradually reduce the frequency of watering, allowing the soil surface to dry slightly between applications. Slowly acclimate the plant to lower humidity to ensure long-term survival.