Separating hydrangeas, commonly known as division, is a method of vegetative propagation used to create new, genetically identical plants from an established parent shrub. This technique involves carefully splitting the root crown and attached stems of a mature plant into smaller sections, each capable of growing independently. Successful division relies heavily on selecting the appropriate type of hydrangea for the procedure and using the correct methodology.
Identifying Hydrangea Types and Propagation Methods
The ability to successfully divide a hydrangea is fundamentally determined by its growth habit, which varies significantly among the different species. Hydrangeas are generally categorized into two main groups: those that grow in clumps by sending up new shoots from the root crown, and those that grow with a more cane-like structure. Only the clump-forming varieties are reliably propagated through division.
The Smooth Hydrangea (Hydrangea arborescens), such as the popular ‘Annabelle’ cultivar, naturally spreads by producing suckers, making it an excellent candidate for division. This growth habit means the plant has multiple distinct crowns that can be physically separated with minimal trauma to the overall root system. The Oakleaf Hydrangea (Hydrangea quercifolia) also tends to form colonies and can often be divided successfully.
In contrast, cane-growing varieties, including the Bigleaf Hydrangea (H. macrophylla) and the Panicle Hydrangea (H. paniculata), possess woody stems that originate from a single, centralized crown. Attempting to divide the dense root mass of these types typically causes excessive stress, often leading to the death of the new sections or the parent plant. Propagation for these shrubs is more successful using alternative methods, such as taking softwood stem cuttings or employing ground layering techniques.
The Process of Dividing Established Plants
For suitable clump-forming hydrangeas, the best timing for division is during the dormant season. This is either in early spring as new buds swell or in early fall, at least six weeks before the first hard frost. Watering the parent plant deeply the day before helps hydrate the root tissues and makes the soil around the root mass more manageable, mitigating transplant shock.
Begin by using a sharp spade to dig a wide circle around the perimeter of the shrub, following the drip line to include a substantial portion of the root system. Carefully lift the entire root ball from the soil, minimizing damage to the finer roots. Once the root ball is out, gently shake or brush away excess soil to expose the individual root crowns and connecting rhizomes.
The separation process requires a clean, deliberate cut. Identify natural sections of the root mass that contain a cluster of roots and at least one to three healthy stems or viable buds. Use a sharp, sterilized knife, soil knife, or spade to slice cleanly through the connecting roots and the crown tissue. Avoid rough tearing of the root mass, as clean cuts heal faster and reduce the risk of disease.
Each resulting division must possess a robust portion of the root system to support new growth. Immediately after separation, replant the new sections in their permanent, prepared locations at the same depth they were previously growing. Planting the divisions slightly higher than the surrounding soil can improve drainage and prevent crown rot. Backfill the planting hole with soil and gently tamp it down to remove large air pockets.
Essential Aftercare for New Divisions
The immediate steps following replanting are essential for the successful establishment of the new divisions. After placing the plant in its new hole, the soil must be thoroughly saturated with water to settle the earth and ensure maximum root-to-soil contact. This initial watering is critical for the survival of the newly exposed roots.
For the first few weeks, maintaining consistently moist soil is necessary, as the compromised root system cannot efficiently draw water. Gardeners should aim to water the new divisions every one to two days, especially without rainfall, ensuring the soil is damp but never waterlogged. Applying an organic mulch, such as shredded bark, in a two- to three-inch layer around the base helps conserve soil moisture and regulate the temperature of the root zone.
New divisions are susceptible to stress from intense sunlight and heat, which can manifest as sudden wilting or drooping leaves. Providing temporary partial shade during the hottest part of the afternoon, or planting the division in a location that receives morning sun and afternoon shade, reduces the likelihood of transplant shock. The plant will focus its energy on growing new fine roots. New leaf growth in the weeks following division signals that the plant is successfully established in its new location.