Shamrock Hydrangea macrophylla, ppaf, cpaf

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A cool new Hydrangea in the Japanese tradition with masses of large, doubled, pink lace-cap flowers. Flowering begins in July and as the season progresses they transform into breathtaking shades of red and deep pink. On acid soils the flowers are more violet. Very floriferous and long blooming. More compact and tends to be more frost resistant than most Japanese types. Developed by the world famous French hydrangea expert Corinne Mallet. This superb new plant pays tribute to Association des amis de la Collections D'Hydrangea Shamrock (French Hydrangea Society) and a portion of the royalties are used to support their Hydrangea collection near Dieppe in Upper Normandy.


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Hardiness: Zone 5

Bloom Time: Mid-summer to fall

Bloom Color: Doubled, pink or blue flowers turn to red or dark blue later in the season

Foliage Color: Glossy, green

Size: 3.5-5 feet tall and wide

Exposure: Full sun to partial shade

Soil: Well-drained soil

Pruning: Shamrock Hydrangea forms its 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.

As a young plant it is best to prune or pinch your plant in order to build a full bodied, well branched plant. If the plant is leggy when you purchased it, shear the plant back hard by 1/3 to 1/2 its original size. Once it puts on an inch or two of growth, pinch the branch tips to remove just the growing tip. This tip controls branching. Once it is removed the buds below it will turn into stems. Once these new branches grow an inch or two, pinch the tip out again. You can repeat this throughout the first growing season as you are tending your garden. Although you will sacrifice one year of bloom, this technique results in a well branched, full bodied plant that will have more flowers in subsequent years. The second season in the ground, repeat the pinching practice (or lightly shear) up until mid-August. Cease pruning and pinching to allow the flower buds to set.

During the third and subsequence seasons, prune or pinch as necessary after flowering and before bud set in mid-August. Do not be afraid to prune or shear your plant harder if you wish to maintain a shorter size.

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

Wildlife: None

Type: Deciduous

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.

Breeder: Corinne Mallet

A cool new variety of hydrangea in the Japanese tradition. Delicate, doubled florets are more refined than those of the more familiar mophead hydrangeas.

Flowering begins in July with pink or blue flowers (depending on soil pH). As the season progresses, bloom color deepens into rich red or violet. This variety is very floriferous and long blooming

‘Shamrock’ is somewhat more compact than other hydrangea varieties, and may be slightly more frost resistant.

Hydrangea fans take note: a portion of the royalties this plant earns are used to support the hydrangea collection of the French Hydrangea Society near Dieppe in Upper Normandy. Who knows what exciting new varieties may come out of this respected breeding program?

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