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How do I prune my hydrangeas?
Hydrangeas are classic garden shrubs prized for their beauty, durability and diversity of flower color – from pink to purple and blue to white. These deciduous, medium to large shrubs provide color from midsummer to autumn when few other plants are in bloom. There are many different types of hydrangeas; many require different methods of pruning. It is important to know the identity of the hydrangea in the landscape so the proper pruning technique can be implemented.
Hydrangea macrophylla – Mophead or Lacecap Hydrangea Zone (5)6-9 and Hydrangea serrata Zone (5)6-7
This is a commonly grown hydrangea with either large globe-shaped flowers (mophead) or flattened heads of tiny fertile flowers surrounded by a ring of larger, sterile, showy sepals (lacecap). It is frequently forced by florists and sold as an indoor pot plant during the spring season. Once moved outdoors, flower color is dependent upon the availability of aluminum in the soil and the pH of the soil in which it is grown: blue if acid; pink if alkaline. There are also several white flowered cultivars. Pruning can be accomplished at two different times: late summer or early spring. Late summer is more widely practiced since this type flowers only from the end buds of upright or lateral shoots produced during late summer and fall of the previous season. Prune as soon as the flowers have faded and strong shoots are developing from the lower parts of the stems and crown. Remove at the base some of the weaker shoots that are both old and new. Always try to keep several stems of old productive wood, with a sufficient number of stout new stems that will flower the following season. Early spring pruning (March), although acceptable, may result in the sacrificing of bloom for that growing season. This is a topic of debate among experts. Many suggest to perform only deadheading (removal just below the flower) or clean-up (removal of shoots damaged by winter or late spring frosts) pruning at this time, especially when growing this species in colder zones. Pruning this species too late in the fall (September) is harmful. New growth, both vegetative and reproductive, will not develop proper maturity which increases its vulnerability to winter dieback.
Hydrangea arborescens – Smooth Hydrangea Zone 4-7(8)
This hydrangea is grown for its huge white blooms which appear in profusion in spring and summer. Many gardeners grow this species in hedges. It can be pruned to the ground line each winter or early spring because it flowers abundantly on new growth, and is frequently killed back during winter. If a larger shrub is desired (3+feet) and/or it is not killed back over the winter, prune less severely. Create a woody framework by removing some branches to the ground; cut others back at varying heights from 1 to 3 feet.
Hydrangea paniculata – Panicle Hydrangea Zone 4-8
This is a commonly planted hydrangea because of its massive displays of large, white, panicle-shaped flowers in mid to late-summer. They gradually turn pink and remain on the plant in a semi-dried condition long after the leaves have fallen. Pruning involves the removal of dead flowers, if unattractive, and annual corrective pruning of vigorous shoots. This species responds very well to annual pruning by producing much larger flower heads. Thin and/or cut back the previous season’s growth in late winter or early spring, since flower clusters occur on newly developing branches. Without regular pruning, this hydrangea can rapidly become overgrown and out of scale in the landscape. It can, however, be developed into a single or multi-stemmed tree form. It is best to promote a strong woody framework when these plants are young. Cut back all weak branches leaving 3 or 4 of the strongest measuring at about 10-24 inches. When established, prune out all lifeless stubs and prune back all the shoots to their lowest pair of healthy buds above the woody framework.
Hydrangea quercifolia – Oakleaf Hydrangea Zone 5-9
This plant is grown primarily for its oak leaf shaped foliage, excellent fall color, attractive flowers, and interesting winter bark. It is ideally suited to a lightly shaded or protected location, and if grown in an exposed site, it is subject to some winter dieback. Prune out any dead wood in early spring. Cut back just to the point of injury and periodically remove a few of the oldest stems to the base to stimulate new growth and create a more dense habit. Flowers develop on old wood so any additional pruning (only minimal) should take place after the flowers are spent.
Hydrangea anomala subsp. petiolaris – Climbing Hydrangea Zone 4-7(8)
This is a desirable mid-summer flowering woody vine that attaches itself by aerial roots to brick, masonry, or wood. Flowers appear on the previous year’s lateral (side) shoots. As young plants, tie shoots to their support structure until they form aerial roots. Once established pruning should be kept to a minimum. If certain shoots have grown out of bounds, reduce their length along with any outward growing laterals to allow more sunlight into the canopy. To promote good flowering, deadhead all shoots that have flowered to a healthy bud.