Hydrangeas are popular flowering shrubs known for their large, colorful blooms. While these bushes grow significantly larger each year, they do not “multiply” like a groundcover or perennial. Hydrangeas are woody shrubs that increase in size through maturation, requiring intentional effort to increase their overall number. True multiplication, or propagation, involves specific techniques to create separate, genetically identical plants from the original shrub. This process is often simpler than many assume, allowing gardeners to expand their collection or share varieties.
Do Hydrangeas Naturally Spread
Hydrangeas are clump-forming shrubs that expand outward from a central crown. This growth habit results in a single, increasingly large bush, not a spreading colony of individual plants. They do not produce the long, underground runners or rhizomes that allow aggressive spreading.
The perceived spreading is usually due to the natural expansion of the root ball, which supports a wider canopy of branches. The Smooth Hydrangea (Hydrangea arborescens) is an exception, as it can produce suckers, or new shoots, from its root system near the parent plant. This natural suckering is a slow, gradual process and does not result in rapid multiplication. Gardeners must intervene to create separate, new hydrangeas.
Creating New Plants Through Ground Layering
Ground layering is the easiest and most reliable propagation method because the new plant remains attached to the parent. The parent provides a steady supply of water and nutrients, sustaining the developing roots and minimizing the risk of failure. Spring or early summer is the best time to begin layering while the plant is in active growth.
Select a long, flexible, non-flowering stem, usually on the outer edge of the bush, that can be bent down to touch the soil. Where the stem touches the ground, lightly injure the bark by scraping away a small, one-inch section from the underside. This injury encourages the formation of new roots from the stem’s cambium layer.
After scraping the stem, bury the injured section a couple of inches deep in a shallow trench. Secure the stem firmly in place using a landscape staple, bent wire, or a heavy object. The tip of the branch should be left exposed and pointed upward, and the buried section must be kept consistently moist. Roots can form within a few weeks, but it is recommended to wait a full growing season, often until the following spring, before severing the connection and transplanting the new shrub.
Propagation Using Stem Cuttings and Root Division
Taking stem cuttings is an efficient alternative for gardeners who want multiple new plants or lack a flexible stem for layering. The most successful cuttings are taken from softwood—the pliable, new growth of the current season—typically from late spring to mid-summer. Select a non-flowering stem and cut a four to six-inch section just below a leaf node, where rooting hormones are most effective.
Preparing the cutting involves removing the lower leaves to prevent rotting and reducing the size of the remaining top leaves to limit moisture loss. Dipping the cut end into a powdered or gel rooting hormone is recommended, as the synthetic auxins stimulate root development. The prepared cutting should be planted in a sterile, well-draining medium, such as a mix of peat and perlite. Keep the cutting in a warm location with bright, indirect light. Maintaining high humidity, often by covering the pot with a plastic dome or bag, prevents the cutting from drying out before roots form, which takes two to four weeks.
Root division is best suited for older, established hydrangeas that produce new shoots from the base, such as Smooth Hydrangea (Hydrangea arborescens) and Bigleaf Hydrangea (Hydrangea macrophylla). This process involves separating the root crown into smaller sections. It is ideally performed in the dormant season during early spring or late fall. The entire plant is carefully dug up, and the root mass is divided using a sharp spade or knife. Ensure each new section has a healthy cluster of roots and at least one or two stems with growth buds. This method immediately yields a small, transplantable shrub.