Hydrangeas are classic garden shrubs known for their bold leaves and long lasting clusters of flowers in shades of white, pink, red or blue, blooming from mid summer to autumn.
All types prefer humus-rich, well drained soil. All types also are not very drought tolerant. They appreciate deep watering, especially in the summer, even once established. BIGLEAF, CLIMBING and ASPERA hydrangeas prefer part shade because they are not able to stay hydrated during hot days in the afternoon sun. SMOOTH, PANICLE and OAKLEAF hydrangeas tolerate full sun after getting established.
BIGLEAF HYDRANGEAS - H. macrophylla and H. serrata ...are typically divided into two types:
• MOPHEADS have massed clusters of petals forming big, rounded heads.
• LACECAPS have a colorful ring of petals surrounding a central cluster of smaller, fertile flowers, imparting a flatter, more disk-like shape. Most Hydrangea serrata varieties are lacecaps. Both types grow as rounded mounds generally 4 to 7 feet high and wide. Dwarf forms are often available.
Hydrangeas don’t require pruning. We recommend deadheading the flowers as they start to fade and minor rejuvenation pruning of old specimens. Studies have shown that floral shows suffer with pruning. Bigger flowers may be produced the following year because of pruning, but there will be much fewer of them than if the plant was never pruned. If a short statured plant is desired, it is best to get a dwarf variety than to set yourself up with constantly pruning a large growing variety. Older plants however, may benefit from some rejuvenation pruning. Prune a Bigleaf Hydrangea just after flowering in late summer. If pruning is delayed too long after flowering, the flower buds for the following year may get removed and the plant will not have sufficient time to develop new ones.
Remove any dead, damaged, diseased or crossing branches. Then thin the plant by cutting out the oldest (woody) branches back to the main trunk or to the ground. The more a branch is exposed to light, the more it will tend to flower.
Changing Flower Color
While Bigleaf varieties are bred for a certain color, that color may be altered somewhat by adding specific elements to the soil when planting, and each fall or spring, well ahead of bloom time. For blue colors - add aluminum sulphate (sold as “blueing formula,” which may be applied any time of year) and for pinks and reds - add dolomite lime. Avoid planting pink hydrangeas with acid loving plants such as rhododendrons, azaleas and berries. Tap water is often slightly alkaline and thus may turn flowers more pink, especially in containers. Some varieties are resistant to any color changes.
PANICLE HYDRANGEA - Hydrangea paniculata
Panicle Hydrangeas are the upright Hydrangea. They can be trained into “tree” forms if desired. Massive display of huge, cone-shape flower clusters which start white and gradually turn pink, often drying and remaining on the plants for months. Typically they grow to 8-12 feet tall without pruning.
Usually involves removing spent flower clusters if unattractive (in fall), and thinning or heading back vigorous shoots (in late winter/early spring).
OAKLEAF HYDRANGEA - Hydrangea quercifolia
These have bold, oak-shaped leaves (bigger in shadier locations), which turn a wonderful bronze or crimson in the fall (better color in sunnier locations). The flowers are in the form of a 10-inch long cluster which starts white and fades to pink. Height can reach about 6 feet.
The Oakleaf blooms on last year's growth. Prune in late summer. If you need to prune a lot of the plant, do so as early in the summer as you can, so it has time to develop flower buds for the following year.
SMOOTH HYDRANGEA - Hydrangea arborescens
These have huge white flowers on dense, upright plants up to10 feet high, except ‘Annabelle,” which grows only 4-6 feet.
Usually involves removing spent flower clusters if unattractive (in fall), and thinning or heading back vigorous shoots (in late winter/early spring). They can be pruned heavily if desired.
ASPERA LACECAP HYDRANGEA - Hydrangea aspera
These have similar flowers to the lacecap, but are blue in the center surrounded by a ring of white or pink flowers. Some varieties have big, fuzzy, almost tropical-looking leaves. These hydrangeas are taller and wispier than the bigleaf varieties. They typically grow to 8-12 feet tall and 6 feet wide.
These plants have a nice natural shape and it is usually not necessary to prune them, except to remove dead or damaged wood. H aspera bloom on old wood, so if desired, prune right after flowering in late summer.
CLIMBING HYDRANGEA - Hydrangea anomala petiolaris
A desirable mid-summer flowering woody vine that attaches itself by aerial roots to brick, masonry, or wood. Blooms are cream-colored, lacy and delicate and the flakey bark is attractive in winter. It requires little or no pruning, perhaps only to thin or direct growth. If certain shoots have grown out of bounds, reduce their length in summer.
Hydrangeas make excellent dried flowers to enjoy in winter. Choose mature blooms (whose center sepals are fully open). Remove the leaves and put the stems in water like other cut flowers. Once the flowers have become like paper, remove them from the water and use them in dried arrangements.