Multiplying hydrangeas is an effective way to expand a collection, resulting in new plants that are genetically identical clones of the parent shrub. This vegetative propagation bypasses the genetic variability associated with growing from seed, ensuring the new hydrangea possesses all the desired characteristics, such as specific flower color and size. Hydrangeas are simple to propagate, allowing even novice gardeners to successfully create new specimens using several reliable techniques.
Propagation Using Softwood Cuttings
The most widely used method involves taking softwood cuttings from the current season’s new growth, typically during late spring or early summer when the stems are still flexible. Select a healthy, non-flowering stem segment four to six inches long. Ensure the tissue is green but firm enough to snap when bent, as this young tissue is primed for root development.
Use a clean, sharp blade to make a precise cut just below a leaf node, where growth hormones are concentrated. Strip all the lower leaves from the bottom half of the cutting to prevent rotting and minimize water loss. Leaving only the top two leaves intact, or halving larger leaves, helps the cutting focus its energy on generating roots.
Dipping the cut end into a powdered or liquid rooting hormone significantly increases the speed and success rate, though it is not strictly required. Insert the prepared cutting into a sterile, well-draining medium, such as a mixture of peat moss and perlite or coarse sand. This medium provides support while allowing gas exchange and drainage.
Maintaining high humidity is essential for the cutting’s survival, as it lacks roots to absorb water independently. Place the planted cuttings under a clear plastic dome or inside a sealed plastic bag to create a miniature greenhouse environment. Position the container in bright, indirect light, avoiding direct sunlight which can scorch the delicate leaves.
Simple Ground Layering
Simple ground layering is a less intensive method that capitalizes on the plant’s natural ability to root where a stem touches the soil. The parent plant nourishes the potential new plant until roots form. Select a long, flexible, low-hanging stem that can be bent down to reach the ground without breaking. This technique has a high success rate but takes longer than cuttings to yield a transplantable specimen.
Where the stem contacts the soil, gently scrape away a small section of the outer bark on the underside to expose the cambium layer, stimulating root growth. Applying rooting hormone to this wounded area can accelerate the process. Firmly pin the stem down into the surrounding soil using a U-shaped wire or a heavy rock, ensuring the tip remains curved upward and exposed to air and sunlight.
Cover the pinned section with soil, which must be kept consistently moist over the following months while the stem develops its independent root system. The new plant can be safely separated from the parent once a robust root ball has formed, typically within a year of the initial layering.
Dividing Mature Clumps
Dividing mature clumps involves separating the root ball and is most effective for shrub types that naturally spread from the base, such as Smooth Hydrangea (Hydrangea arborescens) and Panicle Hydrangea (Hydrangea paniculata). Division is generally avoided for Bigleaf Hydrangea (H. macrophylla) due to its growth habit. The optimal time for division is either early spring before new growth begins or in the fall after the plant has entered dormancy.
Carefully dig up the entire plant, preserving as much of the root system as possible. Clean the root ball of excess soil to visualize the natural separation points. Use a clean, sharp spade or knife to cut the clump into smaller sections, ensuring each division possesses several healthy stems and a sufficient mass of fibrous roots.
Immediate replanting of the divisions is necessary to prevent the roots from drying out; place them at the same soil depth as the original plant. Thorough watering after planting helps the soil settle around the disturbed roots, minimizing transplant shock. This process yields immediate, sizable new plants, making it an efficient method for rapid landscape filling.
Essential Care for New Plants
Monitoring for signs of successful rooting typically becomes evident when the cutting or layered section begins to produce new leaf growth. A more reliable test involves gently tugging on the base of the stem; if resistance is felt, a root system has likely developed enough to anchor the plant. This rooting process usually takes several weeks for cuttings but significantly longer for layered stems.
Cuttings rooted in high-humidity environments, like under a dome, must undergo hardening off before being moved outdoors or into full sun. This gradual acclimatization involves incrementally exposing the young plant to outside conditions over one to two weeks, starting with a few hours a day in a shaded location. This step prevents the sudden shock that can desiccate the tender foliage.
Maintaining consistent soil moisture is essential for the establishment of the new root system; the soil should be kept moist but never soggy. Once the new plants are actively growing, they can be given a light application of a balanced, slow-release fertilizer. Avoid excessive feeding until the root system is fully established.
Divisions and fully rooted layered plants can be moved directly to their permanent landscape location. Container-grown cuttings should be transplanted once their roots fill the small pot. Transplanting should occur in the mild weather of spring or fall, providing the young plant the best chance to establish itself before extreme summer heat or winter cold.