Monday, August 1, 2011

Dig In- Tips from Nettie at Uncanoonuc



Much beloved by gardeners, Hydrangeas are a large, diverse group of plants that can be vines, shrubs or small trees. The main types grown in Northern climates are discussed below (including descriptive information, cultural and pruning advice) and a section answering frequently asked questions follows.

Hydrangea flower heads are made up of both tiny, fertile flowers and large, sterile flowers (groups of flattened sepals that resemble petals).The ratio of fertile to sterile flowers and their arrangement results in flowers that may be flat, domed, globular or conical. For example, the flowers of lacecap Hydrangeas are comprised of a central disk of fertile flowers surrounded by sterile flowers giving a lovely, flattened pinwheel effect. The flowers of the mophead Hydrangeas are comprised almost entirely of sterile flowers in lush, globular clusters.

Hydrangea petiolaris

Climbing Hydrangea  (Hydrangea anomala subsp. petiolaris)

An exceedingly handsome vine, the Climbing Hydrangea is undemanding and commanding. Climbing by rootlike holdfasts it needs only a wall (brick or stone), sturdy arbor or tree to clamber up. Clothed in gorgeous, glossy, dark green foliage it is festooned for weeks in early summer with large, lightly fragrant, flat-topped, white flower clusters. A Climbing Hydrangea in bloom is a stunning sight. Over the season the flowers fade to a parchment color then to brown. In fall the foliage turns a clear yellow, and winter shows off its exfoliating, cinnamon colored bark. Growing thirty feet and more it can be pruned to a lower height, grown as a sprawling shrub or as a mantle on a stone wall. Climbing Hydrangeas are tolerant of many different light conditions, thriving in full sun to shade. Hardy to zone 4, they prefer rich, moist, well-drained soil. Slow to grow as their root system becomes established, they jump at the third year or so and never look back. Adequate moisture is especially important to young plants, they become more drought tolerant with age. If you want them to climb not sprawl, guide them to their support. Once the vines find it, they won’t need further encouragement. Their outward branching growth habit gives a depth and interest that sets them apart from strictly flat growing vines such as Virginia Creeper or Boston Ivy.

‘Moonlight’ Japanese Hydrangea  (Schizophragma hydrangeoides ‘Moonlight’)
A distant cousin, this vine shares all the cultural advice given for the above. The stunning foliage is large, toothed and tinted with pewter. The growth habit is flat and the enormous, white flower clusters are less rigid. It is gorgeous.

Hydrangea arborescens 'Bella Anna'

Smooth Hydrangea  (Hydrangea arborescens ‘Annabelle’)

There are different varieties of this native American shrub available, but ‘Annabelle’ is the reigning queen. Offering an old-fashioned appeal, it is extremely hardy (zone 3), easy to grow and stunning. Growing four to five feet high and five to six feet wide the stout, mostly unbranched stems should be cut to within a few inches of the ground each spring. They will grow into a rounded shrub of dark green, coarse-textured foliage topped with large (eight to twelve inches across), pure white flower heads from early July all through August. ‘Annabelle’ prefers rich, moist, well-drained soil and will grow well in partial shade to full sun. 
Moisture at the root is the key. They are tolerant of different soil pHs but not of drought. The flowers can be used fresh or dried. Deadheading (snipping off the spent blooms) will give them a neater look for the remainder of the season. You’ve seen selections of Smooth Hydrangea (probably  ‘Grandiflora’, known as Hills of Snow)  thriving around  old farmsteads across New England. ‘Bella Anna’ Hydrangea has large, domed, clear pink flower heads. It is one of the new pink ‘Annabelle’ type Hydrangeas!

Bigleaf  Hydrangea (Hydrangea macrophylla)

This Japanese native is the origin of the countless varieties that exist today and the main player in active Hydrangea breeding programs. For most gardeners this is the quintessential Hydrangea, the Holy Grail. Bigleaf Hydrangeas are also the source of much confusion and disappointment. Hopefully the following information will clear the way to greater success and satisfaction with them.

Most  Bigleaf Hydrangeas grow three to six feet high and wide. Their flowers can be lacecaps or mopheads (also known as Hortensias) in colors ranging from rich reds through pinks and white, to every shade of purple and blue. Bigleaf Hydrangeas grow in partial shade to full sun in rich, moist, well-drained soil. Most Bigleaf Hydrangeas are hardy to Zone 6 which means most of the gorgeous plants you see on Cape Cod are not hardy in Zone 5. Get over it. Microclimates do exist and carefully chosen and sited varieties may perform well, but this is rare. Some enterprising gardeners go to great lengths to protect their plants with burlap enclosures filled with chopped leaves or other organic material. No harm here, but too involved for most. Some may be root hardy but not flower bud hardy. Since most varieties form their flower buds on old (previous season) wood, these buds are killed by low winter temperatures or late spring freezes. A leafy shrub with no flowers results, and nobody is looking for that. (Farther south, where the Bigleaf Hydrangeas are more hardy, improper pruning - in the spring or late fall - has the same unhappy outcome.)  But take heart. There is a hardy Bigleaf Hydrangea and breeders are actively working to introduce more. 

Hydrangea macrophylla 'Endless Summer'
‘Endless Summer’ Hydrangea (Zone 4) was discovered in the fields of Bailey Nurseries in Minnesota by tree and shrub expert (and prominent Hydrangea breeder) Dr. Michael Dirr. It was introduced with a blitz of media fanfare in 2003. Our experience – and that of our customers – has been mixed, but mostly positive. ‘Endless Summer’ is a mophead hydrangea that grows four to five feet high and wide. It does best in partial shade in rich, moist, well-drained soil. We know of some ‘Endless Summer’ that are thriving in average soil exposed to full sun. Most gardeners report wilting foliage and sparse (if any) bloom under such conditions. ‘Endless Summer’ blooms on both old and new wood. Here in Southern New Hampshire, we’ve regularly pruned them to within 6” of the ground each spring. (Live buds further up the stems were too few and too scattered across the shrub to warrant leaving last year’s growth). The plants survived, thrived - and the majority of them bloomed most of the summer on the current seasons growth. Regular deadheading (snipping off faded flower clusters) is recommended. We are still getting to know ‘Endless Summer’, but it is truly a breakthrough plant. Like many of the Bigleaf Hydrangeas, the large, globular flowers will vary from pink in an alkaline or sweet soil with little Aluminum to the much coveted true blue in an acid soil with adequate Aluminum. For gardens with a neutral or higher pH, Aluminum Sulphate will lower the pH and add Aluminum. It is readily available at garden supply outlets and directions for use are on the box. I found that a single application in early summer resulted in heavenly powder blue blossoms. If pink flowers were desired, adding lime would raise the pH. Lime is slow acting and can take a full year to have its effect.  Watching your plants, talking with the folks at your cooperative extension service - who can help you get your soil tested - can determine the best course of action for you.

Hydrangea macrophylla 'Twist N Shout'
‘Twist N Shout’ Hydrangea (Zone 4) is a lovely lacecap. Its cultural requirements are the same as ‘Endless Summer,’ but the look is all its own. Sturdy red stems are clothed in glossy green foliage that turns burgundy-red in the fall. Large, lacy centered blooms are surrounded by either pink or blue flowers depending on the soil (see above). It’s gorgeous.

Hydrangea serrata ‘Bluebird’

The Hydrangea serrata species is related to the Bigleaf Hydrangeas, but has its own characteristics and charms. Hailing from the mountains of Japan and China, it is usually hardier. The stems are slimmer, the foliage smaller and more serrated. The flowers can be lacecaps or mopheads. ‘Bluebird’ is an elegant plant growing four to five feet high and wide with a dense, rounded habit. The foliage is dark green which sets off the lovely violet and blue lacecap flowers that grace the shrub July into August. (The flower color is determined by soil pH and availability of Aluminum, see above.)  Any pruning should be done immediately after flowering. They are best in partial shade in rich, moist, well-drained soil situated in a protected spot. By this we mean not in a frost pocket or out on an exposed hillside, but rather in an ell, corner or other spot that is protected from the prevailing winter winds. Flower buds are set on old wood, so any pruning should be done immediately after bloom (our ‘Bluebird’ blooms on both old and new wood and is a thing of beauty).  Any dead tips can be snipped off in the spring which may even encourage heavier blooming. ‘Blue Billow’ is another recommended lacecap variety.

Hydrangea serrata 'Bluebird'

Hydrangea paniculata 'Limelight'
Panicle Hydrangea (Hydrangea paniculata)

The most common of the Panicle Hydrangeas is the variety ‘Grandiflora’ also known as the  P.G. (or PeeGee) Hydrangea. Common or not, P.G. Hydrangea is a Cary Award winner! (This is a respected program that promotes outstanding plants for New England gardens). Another Asian native, this is the hardiest of the Hydrangeas (Zone 3). Growing ten to fifteen feet high and ten feet wide, they can be grown as a small tree or as a shrub. The tree form has tremendous nostalgic appeal and fits beautifully in a more formal setting. Picture a pair flanking an entranceway to form a double arch. Grown as a shrub they are easy to use in many garden settings. P.G.s grow in partial shade to full sun and thrive in a rich, moist, well-drained soil. They are tolerant of a wide range of soil acidity. From early August on, the coarse textured foliage is covered in showy, conical  flower heads twelve to eighteen inches in length. The flowers are white aging to purplish-pink then to beige and tend to arch the branches down giving the plants a weeping appearance. The flowers are wonderful cut and used fresh or dried. I like the look of the spent blossoms and leave them on the plants going into winter. Deadhead them if you want to. Flower buds are set on current years’ growth, so plants may be pruned in early spring . Tree forms have lower branches removed and top branches thinned to a balanced framework. To achieve a shrub form,  plants are cut back as hard as you desire. The stems should be thinned by cutting some off at ground level and shortening the side branches on the rest. There are several cultivars of Panicle Hydrangea including ‘PeeWee’ which grows only four to six feet high and wide making it perfect for smaller gardens. (Plus, “‘Pee Wee’ P.G.” is fun to say). ‘Tardiva’ and ‘Unique’ are similar to P.G.s in stature but have deeper green foliage topped with very conical, very showy, white flower heads that age to bronzy-pink. ‘Limelight’ Hydrangea is a P.G. with showy, upright, spring-green flower clusters that age to vivid rose-pink.

Oakleaf Hydrangea  (Hydrangea quercifolia)

Another American native, Zone 5 is the northern edge of its hardiness. Flower buds are produced on old wood and may be lost during very severe winters. Oakleak Hydrangea and its cultivars are worth growing for their exceedingly handsome foliage, and here their showy flowers are a bonus. They grow four to six feet high and spread wider having a slow suckering habit. The stems have reddish- brown, exfoliating bark which gives winter interest. The thick, gorgeous, oak-like leaves are rich green in the summer and a lovely chocolate-maroon in the fall. The creamy white, upright, long, showy flower clusters are held above the foliage July into August and age to purplish-pink. Any pruning needed - and some may result in a tighter growth habit - should be done right after bloom time. Grow Oakleaf Hydrangeas in partial shade in a rich, moist, well-drained soil. A protected location (see ‘Bluebird’ Hydrangea above) will result in a happier plant and therefore a happier gardener. ‘Pee Wee’ Oakleaf Hydrangea is a darling compact cultivar growing only two to three feet high and wide. ‘Snow Queen’ Oakleaf Hydrangea grows five to six feet high and four to five feet wide. Multiple sepals give a double appearance to its very upright flower clusters, a very showy look.

Hydrangea quercifolia
Frequently Asked Questions:

Why doesn’t my Hydrangea bloom?

See hardiness ratings and pruning advice for the specific types of Hydrangeas given above. Make sure you don’t have them in a too deeply shaded spot. Avoid over fertilizing, especially with Nitrogen which can result in lush foliage at the expense of flowers. Reread the section on Bigleaf Hydrandgeas.

How can I dry Hydrangeas for winter decorations?

Cut when the flowers are fully open (this is key) and strip the foliage off the stems. Some people put them in containers of water, let the water evaporate and the flowers sit until they’re dried. Others skip the water stage and simply place the flowers in an empty container and wait. I’ve done it both ways. I’d use the water method if the blooms were at all limp when you brought them inside.

Can I make my white Hydrangeas bloom blue (or pink)?  
No. You can dye or spray paint dried blooms, but you can’t change their color in the garden.

I got a potted florist Hydrangea as a gift, can I grow it in my garden?

Probably not. You may get a foliage plant, but not one that blossoms. Reread the section on Bigleaf Hydrangeas.

For more information: HYDRANGEAS for American Gardens.  By Michael A. Dirr. Timber Press, Inc.

For more gardening tips from Nettie at Uncanoonuc, click here.

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