The Bigleaf Hydrangea, or Hydrangea macrophylla, is a garden staple known for its massive, colorful blooms. Gardeners often face the frustrating problem of a healthy-looking shrub that produces only leaves, a mystery that revolves entirely around the question of “old wood” versus “new wood” blooming. Understanding this distinction is the single most important factor in ensuring a reliable summer display from this popular plant. The confusion arises because not all Bigleaf Hydrangeas behave the same way, a difference that directly impacts when and how you should prune them.
Understanding Old Wood and New Wood
The terms “old wood” and “new wood” describe the age of the stem on which the plant produces its flowers. Old wood refers to stems that grew during the previous season and survived winter dormancy. The flower buds for the next year’s bloom are formed on these stems in the late summer or early fall, remaining throughout the winter.
New wood, conversely, refers to the stems that grow in the current season, emerging from the crown or existing branches in the spring. A plant that blooms on new wood forms its flower buds on this fresh growth later in the spring, and these buds open into flowers that same summer. This difference dictates the necessary pruning schedule for maximum bloom potential.
The Traditional Bigleaf Hydrangea
The classic Hydrangea macrophylla varieties, such as ‘Nikko Blue’, established the traditional reputation of the Bigleaf Hydrangea. These original varieties set their flower buds exclusively on old wood, meaning the potential flowers for the following year are present on the shrub’s stems from late summer onward.
A major implication of this habit is the vulnerability of the flower buds to environmental conditions and improper care. Severe winter cold or a late spring frost can easily damage or kill the pre-formed flower buds, resulting in a year with no blooms, or “blind wood.” Similarly, pruning these hydrangeas in the fall, winter, or spring inadvertently removes the stems containing the next season’s blooms. Gardeners who prune these traditional types too aggressively in the spring are literally cutting away their flowers.
The Rise of Reblooming Varieties
Newer cultivars have been introduced that fundamentally change the blooming conversation for the Bigleaf Hydrangea. These modern varieties are often marketed as “reblooming,” “everblooming,” or “remontant,” and include popular names like ‘Endless Summer’. These hydrangeas retain the ability to bloom on old wood, providing the traditional early summer flush of flowers.
Crucially, these varieties also possess the genetic trait to produce a second, later flush of flowers on new wood that grows in the current season. This dual blooming mechanism acts as an insurance policy against bloom failure. If the old wood flower buds are killed by a harsh winter or accidentally pruned off, the plant will still produce flowers on the new stems that emerge later in the season. This breeding breakthrough allows gardeners in colder climates to enjoy reliable blooms from mid-summer until frost.
How to Prune for Maximum Blooms
Successful pruning of Bigleaf Hydrangeas depends entirely on identifying whether the plant is a traditional old-wood bloomer or a modern rebloomer. For traditional, old-wood-only varieties, pruning should be kept to an absolute minimum. The only necessary cuts are the removal of dead, diseased, or damaged wood, which can be done in the spring once new growth clearly shows which stems are alive. If shaping is necessary, it must be done immediately after the shrub finishes flowering, typically by late July, to give the plant time to set new buds for the following year.
Reblooming varieties offer a more forgiving maintenance schedule due to their ability to bloom on new wood. Deadheading, or removing the spent flowers, can be done throughout the summer to encourage the plant to produce new blooms. Light shaping can be performed in the early spring, but heavy pruning should still be avoided until the plant is fully dormant. To promote overall vigor in any established Bigleaf Hydrangea, it is beneficial to remove up to one-third of the oldest, thickest stems right down to the base each year, which encourages the growth of strong, productive new shoots.