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Did you know that pink and blue Hydrangea flowers can change their color? It is commonly thought that soil pH is the reason Hydrangeas can change their flower color. This is, however, only part of the story.
Here is what Michael Dirr, professor of Horticulture at University of Georgia has to say about it in his book Hydrangeas for American Gardens.
“Although pH is often listed as the agent of color change, it is actually an instigator of (a precursor to) the process. If soils are acid, aluminum is available; if more alkaline, then aluminum is tied up in insoluble forms and not readily available for uptake.
So the true story is that high acidity, i.e., low pH, solubilizes (or makes available) aluminum; the reverse occurs at low acidity (high alkalinity), i.e., high pH.”
Interesting huh? He goes on to say that in his opinion, any Hydrangea with a blue or pink sepal color can be changed.
In Portland, we have typically acidic soils due to the deluge of rain we experience in fall and winter……and spring. You may have noticed that it can be difficult to keep your pretty pink flowers from turning blue or lavender because of this. Adding lime to your soil to help raise the pH twice a year, once in September and once in March will help.
If you love blue, you’re in luck. You probably won’t have to add anything for color. If your hydrangea is not turning blue as fast as you would like, try adding aluminum sulfate to the soil around your plant, and make sure that you water it in well, even if it’s raining to make the aluminum available to the roots.
H. arborescens Smooth Hydrangea – Native to the eastern part of the United States, many cultivated varieties exist but the most commonly known is ‘Annabelle’. Annabelle has huge clusters, up to 12” across of flowers that start out white and mature to the color of green apples. Flowers are so large that when it rains, they weigh down stems causing the plant to splay, so some sort of staking support may be in order. The species grows to 5-6’ tall and wide, has leaves with a matte bluish tinge, and is hardy to USDA zone 3.
H. aspera – Incredible red bumpy buds open to soft blue, mauve or pink sterile flowers, rimmed by large white sterile florets in a delicate lacecap arrangement. Excellent foliage is bluish and rough on the surface with a fuzzy reverse and fuzzy red stems. Plants grow to be large shrubs, 7-9 feet tall and wide. With ideal conditions plants may grow as tall as 15 feet. Hardy in USDA zones 6-9, with ideal conditions found in the Pacific Northwest! Lucky us!
H. macrophylla Bigleaf Hydrangea – When most people say “Hydrangea”, this is the one they are thinking of. Fat mophead flower clusters are considered to be heavenly by some and gaudy by others. Lacecap flowers are also available, and are often stronger & bolder than lace-cap flowers of H. aspera or H. serrata varieties. Innovations in hardiness and foliage variations have expanded the market for Bigleaf Hydrangeas in recent years, and they are enjoying a return to vogue. There are really too many to name, but we will attempt to highlight a few that cannot be ignored. H. 'Harlequin' shown here.
Angel Series – A series of Hydrangeas, all starting with the word ‘Angel’, and all having white picotee-edged flowers.
'Ayesha' – One of the rare scented hydrangeas, 'Ayesha' has pale pink, lavender or blue mophead flowers. Individual florets are cupped, giving them a lilac-like appearance.
'Blaumeise' – Steph's favorite, 'Blaumise' has a strong periwinkle blue lacecap flower, held atop strong, not floppy stems, with clean glossy green foliage.
‘Endless Summer’ and its creators and factors (Bailey Nurseries introduced it and University of Georgia researched it), is single handedly responsible for today’s renaissance in the world of Hydrangeas. ‘Endless Summer’ is a remontant Hydrangea, meaning that it blooms on both old and new wood. What this means to you and me, is that it will begin blooming in May (in Portland) and continue to set new bloom until frosts and shorter days slow it down.
To those in cooler parts of the country who experience late frosts, ‘Endless Summer’ will produce flowers even if last year’s growth dies down to the ground. And it’s more cold tolerant, living through temperatures as low as -30 degrees farenheit! Pretty cool. It is not the only remontant type, but it is the most floriferous, and it’s easily the most popular. Mophead flowers are pale pink or blue, and a white flowering form, ‘Blushing Bride’ is next in the series.
'Lady in Red' – Another Hydrangea with a big ad budget, ‘Lady in Red’ boasts pink lacecap flowers that hold their color well, even in acidic soils, new foliage with red tinges and red stems. Fall color is truly the amazing part, and the reason for the name ‘Lady in Red’. Leaves are reported to turn dark burgundy! We’ve seen Hydrangeas with nice fall color, but none as bloody as this.
'Lanarth White' – Large pure white sterile flowers have pointed sepals surround green flower buds that open to small pink or blue fertile flowers.
Sturdy stems and good overall vigor set ‘Lanarth White’ apart from its competition.
'Lemon Daddy' – Lemon yellow leaves are a hot backdrop for huge, 12” pink or blue mophead flowers. Foliage seems to be sturdier than previous chartreuse leaf forms.
'Mathilda Gutges' – Yes, another mophead, but this one is so pH sensitive that it may have dark pink, purple and blue flowers all at the same time.
'Nigra' – Black stems on this exotic hybrid support (you guessed it) mophead pink or blue flowers.
'Pia' – Many love the mophead Hydrangea, and many spend years fighting its gregarious habits. Planted in a place that makes them happy, most Bigleaf Hydrangeas will grow to 4-5’ tall and wider. ‘Pia’ is the exception. Also known as ‘Pink Elf’, this baby matures at 24” tall and wide and sets blooms, even at 6” tall. Flowers hold their pink color well, even in acidic soil. ‘Pia’ is perfect in containers and low shady borders.
H. paniculata - Pee Gee Hydrangea – White cone-shaped flower clusters are prized for fresh and dried flower arrangements. The most common variety ‘Grandiflora’ has mostly large sterile flowers in panicles up to 18” long. Bloom begins in June and as flowers age they will turn pink and eventually dry on the plant.
Other varieties of note are ‘Limelight’, with green emerging flowers, and ‘Tardiva’ (Pictured above), also called the Late Pee Gee Hydrangea, which blooms from August to frost. Leaves are apple green on all paniculatas, and plants can grow up to 8-10’ tall and wider. Pee Gee Hydrangeas are commonly trained into a tree form, making a nice small tree for a container or specimen planting. Pee Gees are one of two types of Hydrangea that can grow happily in full afternoon sun.
H. quercifolia - Oak Leaf Hydrangea Excellent foliage is shaped like large leathery oak leaves with new leaves emerging light green, turning dark green in summer and mahogany &scarlet in fall. Flowers are white and held in cone-shaped clusters that are similar to those of Pee Gee Hydrangea, but panicles are typically tighter and more dense. The variety ‘Snowflake’ is a double flowered form, with sepals stacked on top of each other held on panicles as long as 12-15 inches.
Some Oak Leaf Hydrangeas lack branches thick enough to hold up such huge heavy flowers, but ‘Snowflake’ and ‘Snow Queen’have improved structure and hold flowers upright. Like Pee Gee Hydrangeas, Oak Leaf flowers will start out white and age by first developing pink dots, eventually turning completely pink and drying on the plant. Most Oak Leaf Hydrangeas grow very large, sometimes up to 8-12 feet tall and wide. Many city gardeners don’t have space for such a large addition to the garden, but they can make room for a dwarf cultivar such as ‘Pee Wee’ or ‘Sikes Dwarf’, which will mature at 2-3 feet.
H. serrata - Serrated Leaf Hydrangea – Delicate blue, pink or white flowers and serrated sometimes narrow foliage, often with nice red fall color are typical qualities of Hydrangea serrata. Both lacecap and mophead flower arrangements exist, but lacecaps are more commonly found in commerce. Easily the most popular is the variety ‘Preziosa’ boasting pink flowers that hold their color even in acidic soil, and excellent fall color in the foliage. A number of Japanese lacecap varieties have become available recently. Many have double flowers that look like stars or fireworks surrounding smaller fertile flowers. Serrated Leaf Hydrangeas have not gained the popularity of Bigleaf Hydrangeas, but they deserve just as much attention, offering a more delicate and refined overall look.
Also, be sure to view the GardenTime TV video feature featuring Portland Nursery's Sean Gillman talking about Hydrangea varieties.
Photo credits: Monrovia, Doreen Wynja and Peter A. Hogg Photography
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Genus: Hydrangea from the Greek hydor meaning water, and aggeion, meaning vessel; a reference to cup-shaped fruit
Common Name: Hydrangea
Origin: China, Japan, Himalayas, Philippines, Indonesia, North and South America
Characteristics: The Hydrangea genus is made up of around one hundred species of evergreen or deciduous shrubs, small trees or vines. Leaves are simple and opposite, or in whorls of three. Two different types of flowers are present on most Hydrangeas – fertile & sterile.
Fertile flowers are small and inconspicuous, and are usually found near the center of a cluster surrounded by sterile flowers. Sterile flowers are large and showy.
The most common type of Hydrangea, the mophead or hortensia, has flowers made up of mostly sterile florets. Lace cap flowers have small, fertile flowers in the center, surrounded by a ring of sterile flowers.
Fruit is the thing most Hydrangeas have in common. It is conical with a small opening at the apex.
Culture: The heat of Portland summers require that Hydrangeas generally should be planted with at least afternoon shade. The north or east side of a house are ideal locations for Serrated Leaf Hydrangeas
(H. serrata), Big Leaf Hydrangeas
(H. macrophylla) and Climbing Hydrangeas (H. anomala petiolaris). Pee Gee Hydrangeas (H. paniculata), and Oak Leaf Hydrangeas (H. quercifolia) handle sunny locations better.
Soil should be consistently moist and well-drained, preferably acid with plenty of organic matter. Fertilize with an all purpose fertilizer once before leaves emerge, and once following flowering.
Pruning: For most Hydrangeas, flowers are formed on the previous season’s wood, so in Portland, where winter temperatures rarely cause damage to Hydrangeas, it’s recommended to prune sparingly.
In fall/winter, remove dead flowers as they become unsightly, cutting just above the first set of leaves behind the flowers. When leaves emerge in spring, remove dead twigs.
To rejuvenate, cut out one or two of the oldest branches all the way to the ground, and remove weak or spindly stems.
Pests & Diseases: Hydrangeas are prone to fungal problems, but they are typically not life-threatening. Leaf Spots and Powdery Mildew are the most common diseases in Portland, and they can often be avoided by increasing soil drainage and air circulation in the environment of the plant.
If plants become diseased, remove effected foliage, remove all leaves from beneath the plant in fall when leaves drop naturally, and mulch the ground under the plant.
Fungicides are available in addition to cultural treatment.
Succulent new growth attracts slugs, aphids and deer. All can distort and stunt growth. Slugs can be effectively controlled with bait or beer, Aphids can be washed off with water or insecticidal soap, and there are several sprays out there that will deter deer.