Hydrangeas

Gray Barn Green Thumb Guide

Hydrangea Descriptions

 Bigleaf Hydrangea (Hydrangea macrophylla)   is a rounded shrub with either mop-head or lacecap flowers.  Flower color depends on soil type– blue in acid soil and pink in high pH soils.  It grows well in sun or shade in moist, organic-laden well-drained soil.  Plants require abundant moisture and grow 3-6 feet high.  Popular varieties are ‘Endless Summer’ with a longer bloom period, ‘Pia’ a pink dwarf shrub and ‘Nikko Blue’ with deep blue flowers.  With over 500 cultivars, there are many to choose from.

PeeGee Hydrangea (Hydrangea paniculata)  is a large shrub, often trained as a small tree.  Cone-shaped flowers open white in Summer and persist into the fall.  Flowers of ‘Vanilla Strawberry’ change from creamy white to a beautiful pink shade.  ‘Limelight’ flowers open a bright green and slowly change to a deep pink.

 Climbing Hydrangea (Hydrangea anomala subsp. petiolaris) forms aerial roots and can cover walls and fences.  Somewhat slow to establish, it is long lived and usually trouble free.  It tolerates shade or sun and is adaptable to a variety of soils.  White flowers open in June and July, covering this climber with lacy blossoms.

Smooth Hydrangea (Hydrangea arborescens) has large white flowers that bloom in June on a loosely upright shrub.  ‘Annabelle’ blooms can be up to 12” in diameter and ‘Invincible Spirit’ sports a pink flower.

Oakleaf Hydrangea (Hydrangea quercifolia) grows 5-6 feet high and wide and has lobed leaves that resemble those of an oak tree.  These turn a rich burgundy in the fall before they drop.  The long panicles of flowers bloom white during the summer.  This handsome, all-season plant grows in full sun to partial shade in moist well-drained soil.

Moisture and Hardiness

Hydrangeas need water during our dry summers.  They will begin to wilt during hot temperatures or drought, but recover quickly when given water.  Late spring frosts can damage new growth.  As a consequence, plants will produce less flowers.

Pruning

 Blooms on old wood.  This means that these plants grow a stem in the spring and bloom on that stem the following spring.  If you cut those stems off, there will be no flowers.  Bigleaf Hydrangea and Oakleaf Hydrangea both bloom on old wood and consequently do not respond well to heavy pruning.  To rejuvenate this type of hydrangea, first take out the dead wood (be careful, hydrangea canes often look dead when they are not—living canes will have some green inside).  Next take out a few of the crossing canes, especially those that are too crowded in the center.  Cut off canes lying on the ground or touching the house.  Cut these canes all the way to the ground. Deadhead flowers in fall or spring.

Blooms on new wood.  These plants bloom on the current season’s growth, so they generally start blooming later than those that bloom on old wood.  If you are unsure what type of hydrangea you have, observe the bloom time and let the plant tell you how to prune it.  If it blooms early to mid-summer, prune lightly.  For late bloomers, it’s okay to cut them way back.  The PeeGee Hydrangea and the Smooth Hydrangea both bloom on new wood and are consequently late bloomers.  They respond remarkably well to annual pruning, although they do not require it.   In late winter, cut the stems back to two or three buds, or 18 to 24” from the ground, similar to a rose bush.  This will encourage larger flower size.

 Resources

Dirr’s Hardy Trees and Shrubs by Michael Dirr, 2011

Encyclopedia of Hydrangeas by C.J. Van Gelderen and D.M. Van Gelderen, 2004

Guide to Pruning by Cass Turnbull, 2004

Hydrangeas for American Gardens by Michael Dirr, 2004

Hydrangeas:  A Gardener’s Guide by Toni Lawson-Hall and Brian Rothera, 2005

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