How to Prune and Care for Hydrangeas

There are six species of Hydrangea regularly grown in North American garden landscapes:

• H. anomala subspecies petiolaris (Climbing hydrangea),
• H. arborescens (Smooth hydrangea),
• H. macrophylla (Bigleaf hydrangea),
• H.serrata,
• H. paniculata (Panicle hydrangea) and
• H. quercifolia (Oakleaf hydrangea).

Pruning times and methods for each of the six should be accurate to ensure excellent flowers and good plant form. Below are specific instructions for each of the six.

H. anomala subspecies petiolaris (Climbing hydrangea) – Photo #1

A clinging vine with rootlike holdfasts introduced from China in 1865. This hydrangea grows and flowers well in Plant Hardiness Zones 5 – 8. Flowers develop from the lateral shoots of the previous year’s wood.

Climbing hydrangea requires little to no pruning in the first years after planting because it grows and climbs very slowly during this period. Prune established plants minimally but immediately after flowering to allow flower buds to establish for the following year. Prune elongated shoots and lateral branches back to a healthy bud.

Old overgrown vines tolerate hard pruning in early spring that leaves only the bare bones structure. This type of pruning reduces flowering for several seasons. It is probably to the garden’s advantage to spread hard pruning out over several years.

H. arborescens (Smooth hydrangea) – Photo #2

A native low-growing rounded shrub introduced to horticulture in 1736, it grows and flowers well in Zones 4, possibly 3, to 9. Flowers develop from current season’s wood.

Smooth hydrangea plants sucker from roots and become an unmanageable mass with little or no pruning. The best time to prune and thin old canes is in late winter (south) or early spring (north) before the plant starts active growth. If cut to the ground, the new growth produces stunningly large flower clusters in June through July.

H. macrophylla (Bigleaf hydrangea) and H. serrata – Photo #3

“H. serrata is in every degree as diverse (floristically) as its big sister, H. macrophylla,” states retired University of GA, (Athens) horticulture professor Michael A. Dirr on page 155 in Hydrangeas for American Gardens, 2004.

Introduced from Japan and Korea in 1870, H. serrata is less well-know in North America than Bigleaf hydrangeas. It grows and flowers well in Zones 6, possibly 5, to 7.

Mention hydrangea and most gardeners usually think of some kind of Bigleaf hydrangea (H. macrophylla). Introduced from China to England at the end of the 18th century, popularity of these plants spread to France and from there to the United States at the beginning of the 19th century. They grow and flower well in Zones 6 to 9, and sometimes with careful siting in Zone 5.

Both H. macrophylla and H. serrata bear flowers on the previous season’s wood. n warmer climates, they should be pruned immediately after flowering; in colder areas leave old flowers on over winter and prune in mid-spring. Prune stems that have flowered back about 12″ to a set of fat buds.

Keep plants in good form by cutting out old, non-flowering branches at ground level. Remove thin and weak branches completely at ground level or cut to any existing strong bud.

The Endless Summer® Collection of remontant (reblooming) hydrangeas developed from H. macrophylla usually needs no pruning. Plants bloom from previous season’s wood as well as from current year’s growth. Prune out dead wood along with thin and weak wood at ground level.

H. paniculata (Panicle hydrangea) – Photo #4

Sometimes called tree hydrangea, panicle hydrangea may be trained into either shrub or tree form. This is probably the most cold hardy hydrangea, growing and flowering in Zones 3 to 8. Introduced to N.A. horticulture in about 1860, it flowers in mid to late summer on current season’s wood.

Prune in early spring to a low pair of healthy buds for large flowers. Establishing a woody framework is essential to keep panicle hydrangea neat. This framework may be as low as 10″ for specimens or low hedges, or 2′ or more at backs of borders or tall hedges.

H. quercifolia (Oakleaf hydrangea) – Photo #5

A native woodland plant, introduced to horticulture in the early 19th century, Oakleaf hydrangea grows and flowers best in Zones 5-9. It flowers from previous season’s wood, but leaf buds may not be injured by cold as much as flowers buds are. Autumn leaf color is an outstanding red-purple color.

Pruning is minimal except for cleaning out winter dieback, removing thin, weak stems along with old inflorescences in mid to late spring.

Dirr on page 132 in Hydrangeas for American Gardens, 2004 states, “The foliage (of H. quercifolia) is exquisite and provides justifiable reason to grow this plant in northern gardens (Zone 5).”