Growing Hydrangea (Shrub)

Pronunciation: hye-dran'jee-uh 

This variable group is beloved for its delicate clusters of papery flowers, borne between July and September depending on the variety. Some types are shrubby while others are more treelike; all bring a stately, old-fashioned feel to the landscape. Most grow quite quickly under good culture, and are long-lived.

Some Hydrangea macrophylla varieties flower on old wood, and must carry their flower buds through the winter. Early or late freezes may damage flower buds and prevent them from blooming. For example, in Zone 5, bloom may only succeed 3 years out of 5, but the plant itself is hardy there. Fortunately for gardeners in colder zones, recent introductions will bloom for them, as they flower on new growth as well as year-old stems, so blossoms are guaranteed even after a cold winter.

Climbing Hydrangea (H. anomala petiolaris) will grow and flower even in a northern exposure. This large, heavy vine has lateral branches that will grow out as much as 3′ from the supporting structure. It is superb for growing up the trunk of large shade trees, walls, or along a stonewall. The reddish brown, peeling bark is attractive in winter. Although growth is slow the first couple of years after planting, this species is vigorous once established. Blooming usually begins in 3–5 years.

Light/Watering: Most varieties tolerate full sun in the North, but benefit from afternoon shade. In the South, plants require afternoon shade. Moist soils that do not dry out are best; do not plant in hot, dry, exposed sites. Mulch to conserve moisture and buffer soil temperatures.

Fertilizer/Soil and pH: Fertilize once in spring with a fertilizer designed to encourage blooms (such as 15-30-15). Soils should be moist but well drained, and rich in organic matter. In some varieties (H. macrophylla and H. serrata), flower color is determined by the pH of the soil; at low pH (acid soils) flowers will be blue and at higher pH, flowers will be pink. Generally, a pH below 5.0 results in deep, vivid blues and as the pH rises the flowers range from blue to lavender to mauve to a vivid deep pink at pH 7.0 (neutral). The pH determines the availability of aluminum in the soil; this element is more readily available in acid soils, and this availability results in the blue flower color. Since phosphorus ties up aluminum in soils, using a fertilizer low in this nutrient will aid in attaining blue flowers. If pink flowers are desired and your soil is acid, simply add lime to raise the pH and use a balanced fertilizer. Aluminum sulfate will lower pH if blue flowers are desired.

How to test your soil?

We recommend that you visit your local Cooperative Extension Service to find out about soil testing in your area. Follow this link for a directory of institutions involved in the Cooperative Extension program.

We also offer a Soil pH Meter, which allows you to test your soil and provides quick, accurate results.

For our complete selection of Hydrangea growing supplies, click here.

Pests/Diseases: None serious. Occasionally powdery mildew will infect the foliage, especially in humid areas with poor air circulation. Treat with an appropriate fungicide if the problem is serious, and be sure to rake up and destroy all fallen foliage in the autumn.

Companions: Old-fashioned tawny Daylilies are a classic combination with the PeeGee or Tree Hydrangea (H. paniculata 'Grandiflora'). Astilbes and Oriental Lilies in shades of rose, pink, and white are lovely with the shrubby Hydrangeas.

Pruning: The pruning of Hydrangea shrubs varies by variety, as some flower on old wood and some on new, and others on both.

Hydrangea anomala petiolaris (Climbing Hydrangea): Remove any dead wood in early spring. Prune as needed after flowering. Blooms on old wood.

Hydrangea arborescens (Smooth Hydrangea): If desired, prune to shape plants and remove any dead branches in early spring. If your shrub is too large, prune to desired height in fall or early spring. This includes H. a. 'Annabelle,' H. a. Bella Anna™, H. a.  'Haas' Halo,' H. a. Incrediball®,  H. a. Incrediball® Blush, H. a. Invincibelle® Spirit, H. a. Invincibelle® Spirit II, and H. a. Lime Rickey®. These varieties bloom on new wood.

Pruning: If your Hydrangea is growing too large, prune to the desired size by the end of August. In spring, only prune out dead wood once the new growth has emerged. This includes H. m. 'Big Daddy,' H. m. Cityline® Mars, H. m. Cityline® Rio, H. m. Cityline® Venice, H. m. Color Fantasy®, H. m. Double Delights™ Star Gazer, H. m. Everlasting™ Amethyst, H. m. 'Lady in Red,' H. m. Light-O-Day®, H. m. 'Nikko Blue,' H. m. Pink Shira™, and Paraplu®. These varieties bloom on old wood.

For mophead varieties blooming on both old and new wood, by the end of August cut back stems by about half if plants are growing too tall. Remove some of the oldest stems at ground level to thin out the shrub as needed. In spring, only prune out dead wood once the new growth has emerged. This includes H. m. 'Blushing Bride,' H. m. Double Delights™ Star Gazer, H. m. Endless Summer®, H. m. Endless Summer® Bloomstruck™, H. m. Everlasting® Revolution, H. m. Let's Dance® Big Easy, Let's Dance® Blue Jangles®, H. m. Let's Dance® Moonlight, Let's Dance® Rave™, H. m. Let's Dance® Starlight, H. m. Mystical® Opal, H. m. Nantucket Blue™, H. m. Pistachio, and H. m. Twist-n-Shout™.

Hydrangea paniculata (Panicled Hydrangea): During the first few years of establishment in the garden, prune in early spring by 1/3 to encourage more branching and blooms. Little pruning is needed beyond removing any dead wood whenever seen. If desired, mature plants can be cut back as needed in early spring. This includes H. p. Bobo®, H. p. 'Bombshell', H. p. Fire and Ice, H. p. Fire Light®, H. p. 'Grandiflora' (PeeGee), H. p. Great Star®, H. p. 'Limelight,' H. p. 'Little Lamb,' H. p. Little Lime™, H. p. Little Quick Fire™, H. p. Mystical® Flame, H. p. Quick Fire™, H. p. Pinky Winky™, H. p. 'Tardiva,' H. p. Vanilla Strawberry™, and H. p. White Diamonds®. These varieties bloom on new wood.

Tree form Hydrangea paniculata : Prune in early spring, removing lower suckers and up to half the older top growth. In the first few years of establishment, branches can be pruned by 1/2 in late fall to reduce toppling over in snowy locations.

Hydrangea quercifolia (Oak Leaf Hydrangea): Young plants benefit from pruning to promote branching, but plants will not flower until the following year. Little pruning is needed beyond removing any dead wood whenever seen. If desired, plants can be cut back to shape as needed after blooming. This includes H. q. 'Alice,' H. q. Gatsby Gal™,  H. q. Gatsy Pink™, H. q. Jetstream™, H. q. 'Little Honey,' H. q. 'Ruby Slippers,' and H. q. 'Snow Queen.' These varieties bloom on old wood.

Hydrangea serrata (Mountain Hydrangea): Little pruning is needed, but if shrubs grow too large, cut back stems by about one-third by the end of August. In spring, only prune out dead wood. This includes H. s. 'Blue Billow,' H. s. 'Fuji Waterfall,' H. s. 'Miranda,' H. s. 'Pretty Woman,' and H. s. 'Preziosa.' These varieties bloom on old wood. H. s. Tuff Stuff™ is a variety that blooms on both old and new wood. If no fall pruning was done, stems can be cut back by one-third in spring if necessary—but this will sacrifice the bloom on the old wood and shrubs will not flower until late summer.

Reflowering: Regularly deadheading the blooms of H. macrophylla that bloom on both old and new wood helps encourage repeat bloom on the current year's growth. You may cut the first flowering stems of H. arborescens 'Annabelle' and hang to dry for arrangements; rebloom may then occur in August or September.

Transplanting: Young plants may be transplanted when dormant in early spring. Prune top growth after transplanting to reduce water loss.

End of Season Care: Rake up and destroy any fallen foliage that was infected by powdery mildew or other fungi. You may wrap H. macrophylla varieties with burlap or other protective covering to help preserve flower buds through a cold winter.

Calendar of Care

Spring:Prune Hydrangea varieties as indicated above, according to their species. Prune out any dead wood from all varieties. Check soil pH and adjust up or down if needed for desired flower color of H. macrophylla and H. serrata. Feed plants with a fertilizer high in phosphorus (such as 15-30-15) to encourage blooms. Complete any transplanting before leaves unfurl. Mulch plants after soil has warmed to conserve moisture and buffer soil temperatures. Watch for powdery mildew and treat as needed.

Summer: As soon as blooms fade, remove spent flowers from H. macrophylla, H. quercifolia, and H. serrata varieties. Cut flowering stems from H. arborescens 'Annabelle' and hang to dry if desired.

Fall: Remove and destroy any fallen foliage that was infected by powdery mildew. If desired, wrap H. macrophylla varieties with burlap or other material to help flower buds overwinter in colder climates.