Pruning Hydrangea is not difficult. You just have to know the type of plant you are growing and when it sets its flower buds:

Pruning Young, Newly Planted Hydrangeas

Pruning Hydrangea - Species List

Hydrangea anomala is the Climbing Hydrangea. 

Pruning: No need to prune - Just train on a tree or a wall

Hardiness:  USDA Zone 4

Cultivars and Descriptions:

This plant is considered by many to be the Cadillac of all vines. It is a strong grower but not so aggressive that it will tare down a house or fence like many vines.  It is in fact poorly suited for a fence because it does not twine but climbs by aerial roolets.  It is at its best when grown on the trunk of a tall oak tree or covering the face of a brick wall.  It blooms from late June to early July.   Its lightly fragrant, creamy white blooms are 6 to 10 inches across and composed of a lacy center of fertile flowers ringed with a bracelet of larger sterile florets.  The effect is breathtaking and any self- respecting designer should include this plant in his or her arsenal of plants. This jewel is also noted for its attractive thick glossy leaves and its rich brown exfoliating bark.

There are several new cultivars of climbing hydrangea that are worth looking for. 'Skyland's Giant' (image above) is a new variety selected for especially large flowers. 'Fire Fly' is a new variegated selection of climbing hydrangea that is simply spectacular in in the spring when the plant flushes. It has the same great flowers as the species. As the season progressed the variegation becomes less pronounced.

Hydrangea arborescens - Smooth Hydrangea. 

Pruning: Forms its flower buds in the late Spring to early Summer: Prune in late fall, winter or early spring. Responds well to being cut back to about 10"-12" above the ground. This give your stronger stems and larger flowers.

The selection White Dome™ hydrangea is very attractive in the winter, so early spring is best for this selection.

Hardiness:  USDA Zone 4

Cultivars and Descriptions:

Everyone knows the large, snowball-like blooms of Snow on the Mountain the common name for the cultivar ‘Grandiflora’.  Unlike the species, this plant does not have the flat flower head composed of mostly fertile flowers.  It has a big ball of sterile flowers that bow to the ground after a heavy rain. The cultivar most commonly grown today is ‘Annabelle’.  This is because it has the extremely large, tight,  symmetrical blooms, reaching up to  14 inches across. It is widely used in the north because it is hardy to zone 4, and because it blooms on new wood.  The wood will often freeze back in the winter but will still reliably bloom from buds produced in the spring  It can be pruned either in the fall or spring, or in mid to late summer after it is finished blooming.  The one negative attribute of ‘Annabelle’ is that its blooms are so big and heavy the plant will often collapse under its own weight.  Staking is often necessary to keep this plant together. White Dome™  hydrangea is a new lace-cap variety that has large lacy dome shaped blooms. It has attractive large dark green leaves and strong flower stems that never flop. This plant is particularly attractive in the winter when the snow settles a top the dried flower heads.

Invincibelle Spirit is an Annabelle type of plant but it is the first with pink flowers. It is very reliable flowering and in fact a strong reblooming plant that keeps making new flowers right up until frost.

Hydrangea macrophylla - the Big Leaf Hydrangea

Pruning:

Big Leaf Hydrangeas typically do not require much pruning - but if you wish to build a tighter plant or maintain a shorter size follow these instructions:

The flower buds form in later summer and then flower the next year in early to mid summer. The best time to prune is it after it blooms, from mid-July to mid-August.  Selectively prune out any dead stems, or old non-flower producing stems. Cease pruning in mid-august to allow time for the flower buds to form prior to winter.

Hardiness:  USDA Zone 5

Watering: High moisture. Moisture is a necessity of this plant.

Fertilizing: Fertilize in early spring by applying a slow release fertilizer specialized for trees & shrubs. Follow the label for recommended rate of application. Flower color is affected by pH. For blue flowers, the soil must be more acidic and for pink flowers, the soil must be more alkaline.   An easy way to induce blue flowers is to add one tablespoon of Aluminum sulfate to a gallon of water and soak the roots in early spring. Treat two times. 

Uses: Groupings or masses, perennial or shrub borders, specimen, screens or hedges, mixed container, cut flowers.

Cultivars and Descriptions:

Extremely popular today because of it is the most colorful of all the species.  Like Hydrangea arborescens, this plant too can be categorized into two main groupings: Mopheads (snowballs) and Lacecaps.  The Mopheads are large round clusters of sterile flowers and the lacecaps are flat heads composed of both fertile and sterile flowers.  The Mopheads are the most popular because we tend to love the gaudy.  The lacecaps are gaining in popularity and are considered by many, including myself, to be even more beautiful because of their delicate looking nature.

Hydrangea macrophylla is unique for several reasons.  It sets it flower buds in the fall and overwinters them.  A hard winter can kill the buds and eliminate flowering. An early  fall or late spring freeze may also result in a loss of flowers.  Although completely root hardy in Zone 5, the buds should be protected with a light mulch in the North to improve the bloom reliability.  Feedback from growers around the country have provided us with valuable information on bloom reliability.  The most exciting news is that the cultivars 'Endless Summer' and Let's Dance™ hydrangea  have the ability to bloom on old and new wood alike. If the buds are winter killed the plant will form new buds in the spring and still bloom. These are great selections for the Midwest where it is hard to get Hydrangea to bloom.

Pink Shira™ hydrangea, Endless Summer, Forever and Ever and other reblooming plants may not be the best choice of Hydrangea if you live on the West Coast, East Coast or the South where big leaf hydrangea blooms reliably. People in these areas have a wonderful array of varieties to choose from, many with superior foliage and flowers. For example - consider the new dwarf cultivars sold under the CITYLINE™ series. These compact plants form a neat compact plant that is covered with blooms.

Flower color -  How to change Flower Color

Another interesting  attribute of this plant is that its flower color may change depending on soil p.H..  It is not the p.H. itself that changes the color, but it is the availability of Aluminum ions that directs the color. Aluminum has greater availability in acid soils thus the blooms turn blue in acid soils.  If the soil is either basic or high in phosphorous, the aluminum is tied up and flowers tend to be pink.  The degree of color change is dependent upon the amount of aluminum ions available and the cultivar itself.  It should be noted that if you are growing in a container your soil mix you may not have much aluminum availability even at low p.H. levels.  Aluminum sulfate treatments would then become necessary to get blue flowers.  If you fertilize your plants be aware that you will tie up the aluminum with high levels of phosphorous. 

Many new and rediscovered cultivars of Hydrangea macrophylla are hitting the market.  It’s real exciting to see so many varieties, but only time will tell which are the best for your area.  New breeding efforts are underway to bring us hardier cultivars and more varieties that will bloom on new wood.  Until then, remember to mulch in the winter and to site these plants in a microclimate for best results.

Hydrangea paniculata (Panicle Hydrangea)

Pruning: Best pruned in early spring. Blooms on new wood. Very tolerant of hard pruning, in fact cutting the plant back from 1/2 to 1/3 will result in larger flowers. Can be pruned in winter but why not enjoy the winter beauty of snow on the dried flower heads.

Some selections, particularly limelight make an excellent hedge.

This is our hardiest species and perhaps the best choice for the Midwest.  How can one help but say “oooh!” when we see this plant change daily from its pure white blooms to hues of warm pink. It is unfortunate that many nurseries sell only the tree form of the cultivar ‘Grandiflora’ which we call Pee Gee or P.G. for short.  This plant is noted for its abundance of sterile blooms on its thick conical flower head.  What is unfortunate is that so few growers, retailers and designers have yet discovered the many excellent cultivars now available. Also, it need not be a tree form to look good.  In fact, the plant shows off its flowers better if grown as a shrub.  I particularly like the cultivar Pinky Winky™ hydrangea which has very large but delicate, lacy flowers.  Its combination of fertile and sterile flowers gives it a soft intricate look. It is also one of the earliest cultivars to bloom and its flower heads continue to grower as the season progresses. This continued growth results on interesting bi-colored because the older flowers turn dark pink while the new flowers emerge white.   Quick Fire™ hydrangea is a very early blooming selection which blooms in late June - early July. It is not as open as Kyushu, but not as dense as Pee Gee.  When used together with other varieties  the bloom period can be extended over three months. Other new cultivars include ‘Little lamb’ which has tighly packed sterile blooms in petit flower heads. The plant is only 3-4 feet tall so it makes a great shrub for around the home.  In the autumn the blooms turn pink  to create a breathtaking floral display.  Perhaps the most exciting news for Hydrangea paniculata comes in two new and markedly distinct new cultivars. Limelight is a fantastic new selection from the Netherlands with exquisite cool green  flowers. The blooms are large and held up on strong stems making a handsome display. The color, may seem odd, but once you seen the flowers you'll be convinced this a great plant that blends wonderfully into any garden or landscape.   In the autumn the bright green flowers transform to shades of pink, burgundy and green all at the same time.

 Hydrangea paniculata The Swan™ Hydrangea is a new plant from Belgium. It's unlike any other hydrangea, with massive sepals the size of your hand. This is a great selection for cut flower or dried flower arrangements, or for the garden. Take note that The Swan is an ugly duckling as a young plant and takes a few years in the garden to mature into a swan.

Oak Leaf Hydrangea, Hydrangea quercifolia,

Hardiness:  USDA Zone 5

Watering: Moisture is a necessity when young. Drought tolerant with maturity.

Fertilizing: Fertilize in early spring by applying a slow release fertilizer specialized for trees & shrubs. Follow the label for recommended rate of application.

Uses: Groupings or masses, perennial or shrub borders, specimen, screens or hedges, mixed container,

Cultivars and Descriptions:

A great landscape plant. As its name indicates it has an oak-shaped leaf.  It is noted for its unrivaled  burgundy red fall color.  It blooms in late June - early July and is persistent into winter.  The flower heads are cone-shaped, open white and fade to a pleasing pink and then rich brown. The plant is 6 to 10 feet tall, course in texture, and very useful in the landscape. It sets it buds in the fall and exhibits excellent bud hardiness.  It should thrive in zone 5 even though it is native to the Southeast.  Due to its variability when grown from seed, I recommend the use of its fine cultivars. ‘Snow  Queen’ has consistently good fall color and very large florets arranged in large, erect, dense heads.  ‘Snowflake’ is a doubled flowered form that combines pink and white florets on the same flower.  The extremely large flower heads are so heavy they weep downward making it easy to recognize. Some criticize this attribute, but I like it very much. To each his own!  The cultivar ‘Harmony’ has a very dense, rounded pear shaped flower head with very few visible fertile flowers.  The cultivar ‘Alice’ is also very popular.  It is a selection made by Mike Dirr for its exceptionally fine fall coloration.

Hydrangea serrata - Hydrangea

Hydrangea serrata is considered by some to be a Hydrangea macrophylla variety and not a distinct species. Yes the plants are quite similar in many respects, but I personally view these plants as distinct, and hence treat them here as a separate species. 

Pruning:

Serrata Hydrangeas typically do not require much pruning but if you wish to build a tighter plant or maintain a shorter size follow these instructions:

These Hydrangea form their flower buds in later summer and then flowers in late June. The best time to prune is it after it blooms, from mid-July to mid-August.  Cease pruning in mid-august to allow time for the flower buds to form prior to winter.

Hardiness:  USDA Zone 5

Watering: High moisture. Moisture is a necessity of this plant.

Fertilizing: Fertilize in early spring by applying a slow release fertilizer specialized for trees & shrubs. Follow the label for recommended rate of application. Flower color is affected by pH. For blue flowers, the soil must be more acidic and for pink flowers, the soil must be more alkaline.   An easy way to induce blue flowers is to add one tablespoon of Aluminum sulfate to a gallon of water and soak the roots in early spring. Treat two times. 

Uses: Groupings or masses, perennial or shrub borders, specimen, shade garden, mixed container, cut flowers.

Cultivars and Descriptions:

Unlike H. macrophylla, which is native to the coastal climate of Japan, Hydrangea serrata is native to the mountainous regions of Japan and Korea.  Coming from higher elevations serrata tends to be a hardier plant.  The leaves, as the name suggests, are more serrate “having a saw-like leaf margin”  They tend to be smaller, finer stemmed plants, with smaller more linear leaves and nearly all the cultivars being lacecaps.   ‘Bluebird’ is perhaps the best known of the serrata cultivars.  It has clear blue flowers with lighter blue sterile florets with each sepal evenly space, never touching each other. The leaves take on a coppery-red coloration in the fall which is quite pleasing.  ‘Diadem’ is a dwarf plant reaching only 2 feet. It is free blooming and makes a beautiful display. It is perhaps the earliest blooming cultivar, with the flowers appearing in mid-June.  The bloom is dome shaped, 4-5 inches across, with a soft pink or blue depending on p.H.. The cultivar ‘Beni-gaku’ is a long cultivated Japanese cultivar, often depicted in Japanese art. This very graceful plant reaches three to four feet at maturity.  Its flowers, a delicate pure white lacecap, become tinged with red as they age.  An interesting plant that is considered a cross between macrophylla and serrata is ‘Preziosa’.  Its mophead blooms emerge a pure white and gradually change to  a translucent burgundy red by the end of the season. The leaves undergo a similar coloration change as well. If planted in acid soil the blooms will color an extraordinary blend of pale blue, mauve, violet and pale green.  I have also received a lot of good feedback as to the hardiness and bloom reliability.  This is a remarkable plant by any standards!

Hydrangea Summary

As you can see the genus Hydrangea is an amazing group of plants.  Is it any wonder that they are so popular?  It is a fun group of plants to learn as well.  There are numerous cultivars in each species that I did not mention that are excellent plants and deserve greater use.  This article is an attempt to give you an overview of the usable species in the genus. A small taste to make you hungry and want to learn more about this outstanding group of plants.  There are several excellent books on Hydrangea that can guide you on your Hydrangea journey.  HYDRANGEA species & Cultivars  by Corinne Mallet is a two volume set that is invaluable to the Hydrangea fanatic. It has excellent descriptions and color plates of hundreds of varieties.  The book HYDRANGEAS by Haworth-Booth is also an excellent resource.  Still the best way to learn your Hydrangeas is to start growing them and see for yourself the beauty and excitement these plants create.  And for those of you who felt this article gave your more information that you ever wanted to know about Hydrangea. The name Hydrangea is Greek meaning “water vessel”. It is derived from the shape of its seed capsule.