The butterfly bush, Buddleia davidii, is a vigorous shrub celebrated for its long, colorful flower spikes that attract numerous pollinators. Propagating this plant from a cutting placed in water is a simple and reliable vegetative method that produces a genetic clone of the parent. This technique allows gardeners to easily multiply their favorite varieties without the need for specialized equipment or complex soil mixes. The process relies on the plant’s natural ability to initiate adventitious root growth when its stem is exposed to a water medium.
Selecting and Preparing the Cutting
The best time to take a cutting is during late spring or early summer, which corresponds with the plant’s active growth phase. These are known as softwood cuttings, and these young, flexible stems contain the highest concentration of growth hormones. Select a healthy, non-flowering stem from the mother plant, as flower production diverts energy away from root development.
Using clean, sterilized pruning shears, make a cut just below a leaf node. This is the slightly swollen point on the stem where a leaf or bud emerges, and it contains the highest concentration of auxins, the natural rooting hormones. The ideal cutting should be approximately 4 to 6 inches long.
Remove all leaves from the lower one-half to two-thirds of the stem to prevent them from rotting once submerged. Submerged foliage will decay quickly, fouling the water and creating an environment for bacterial and fungal growth. Leaving a few healthy leaves at the top is necessary for photosynthesis, which provides the energy required for new root cells to form. While rooting hormone is commonly used for soil propagation, it is less necessary for water rooting, but ensuring a clean cut remains paramount.
Monitoring Root Growth in Water
The environment significantly influences the speed and health of root development. A clear glass vessel is often preferred because it allows for unobstructed visual inspection of the rooting process without disturbing the delicate stem. Use filtered, distilled, or rainwater instead of tap water, which may contain chlorine that inhibits growth.
Place the vessel in a location that receives bright, indirect light, such as a north-facing window. Direct sunlight can overheat the water, stressing the cutting and promoting algae growth. The ideal temperature range for rooting is between 65 and 75°F (18–24°C).
Maintaining water quality requires a complete change of water every few days, or at least once a week. This ensures the water remains fresh and oxygenated, preventing the buildup of anaerobic bacteria and stem rot. After a few weeks, small white nubs, known as root primordia, will begin to emerge from the submerged leaf nodes.
Monitor the cutting until the newly formed roots are approximately 1 to 2 inches long and appear firm, white, and healthy. Roots grown in water are structurally different from those grown in soil, as they are adapted to a constantly saturated environment. Waiting until the roots reach this length provides a robust structure to withstand the transition to soil.
Transitioning the New Plant to Soil
The move from water to soil is a delicate shift requiring careful management to prevent transplant shock. Select a suitable, well-draining potting mix, such as standard potting soil amended with perlite or coarse sand for aeration. Avoid using dense garden soil, which may introduce pathogens.
Before planting, “harden off” the cutting to prepare the water-adapted roots for a drier environment. This acclimatization can be achieved by slowly introducing small amounts of potting mix into the water over several days. Alternatively, keep the soil consistently and heavily moist immediately after planting. The goal is to slowly reduce the moisture dependency of the roots.
When planting, create a small hole and gently place the cutting so the new roots are not bent or broken. The root crown, where the stem meets the roots, should be level with the soil surface. Lightly tamp the soil around the cutting to eliminate air pockets.
After transplanting, water the cutting thoroughly until moisture drains from the bottom of the pot. Place it in a sheltered location that receives bright, indirect light. For the first few weeks, keep the soil consistently moist, but never waterlogged, to ease the transition. As the plant establishes itself, gradually reduce watering and slowly introduce it to more direct sunlight before moving it outdoors.