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Hortensia

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  • Trees and Shrubs
Hydrangea macrophylla 'Nikko Blue'
Photo: Gilles Delisle

Onglets

Botany

Origin and description

Known as Hortensias or Four Seasons, these are the pink, white or blue hydrangeas that you buy for Easter or Mother’s Day. These small shrubs (1 m x 1 m) with a rounded growth habit produce an abundance of thick, lightly-branched stems. Each stem is topped with a bouquet of round (Hydrangea type) or flat (marginalis-type) flowers, depending on the cultivar.

To prolong the flowering of your houseplants, see the fact sheet on Hydrangea macrophylla in our section on indoor plants.

Species, cultivars and related plants

The greenish flower buds open into large balls of white, pink or blue blooms, according to the particular variety.

For some cultvats, the colour of the flower depends on the acidity of the potting soil. Blue-flowered varieties like 'Nikko Blue', 'All Summer Beauty', 'Mariesii', 'Perfecta Blue' and 'Endless Summer' need acidic soil (pH of 5.0 to 5.5) to stay blue. Otherwise, if the soil is neutral or alkaline (pH 6,0 à 6,5), they will turn bluish-pink. If you wish to acidify the soil, you can buy various products containing sulphur, iron sulphate or aluminum sulphate from a gardening centre.

The white-flowered cultivars ('Maculata', 'Lanarth', 'Sister Therese', 'Vetchii') are not affected by soil acidity and those with pink flowers ('Bouquet Rose', 'Forever Pink', 'Pink Beauty', 'Masja') do not turn completely blue in acidic soil, but acquire a purple tint.

There are also cultivars with very decorative variegated foliage (‘Light O Day,’ ‘Lemon Wave,’ ‘Maculata,’ ‘Tricolor’).

Toxicity

All parts of the plant are poisonous.

Common name

Hortensia

Latin name (genus)

Hydrangea macrophylla

French common name

Botanical family

  • Hydrangeaceae
Horticulture

Growing conditions

Lighting conditions

Sun or partial shade.

Soil

Rich, well-drained, acidic to slightly alkaline (pH between 5.5 and 6.5). In soil that is too alkaline, iron deficiency can be seen on new leaves (yellowing between the veins). To acidify the soil, it can be amended with pine needles or shredded oak leaves. If necessary, acidifying formulations (sulfur, iron sulfate or aluminum) should be applied before the formation of flower buds.

Hardiness

Barely hardy in our climate, the Bigleaf hydrangea needs a site sheltered from the winter winds, where snow accumulates but does not melt too quickly in the spring (east or north side of the foundation). Although the roots easily survive in Zone 5, stems and flower buds are susceptible to frost (Zone 6), especially during a cold winter without snow. Winter protection required.

Easy to grow?

In their native country of Japan, these small shrubs grow naturally under the tree canopy, sheltered from intense sun and high winds. During the winter, they are protected by a thick layer of leaves and snow.

Pruning and maintenance

Pruning and winter protection

The pruning and protection vary, depending on the cultivar.

  • Cultivars that flower on new wood can be cut flush with the soil (8-10 cm) every fall without compromising flowering. They are well suited to our cold climate, and are sure to flower even in case of severe frost. A light mulch (10 cm) of shredded leaves and the snow cover is enough for winter protection.
    Examples: ‘Early Sensation,’ ‘Forever Pink’
  • Cultivars that bloom on both old and new wood are pruned more lightly. In the fall, cut back the stems by one-third or one-half above a vigorous bud. Cover the stems with a thick layer of shredded-leaf mulch (30 cm) to protect the stems and flower buds. In spring, the mulch should remain in place until danger of frost is past. During the spring, remove any dead wood, and frail or elderly stems. If there is a frost, new shoots will spring from the roots but they will not flower.
    Examples: ‘All Summer Beauty,’ ‘Nikko Blue,’ ‘Endless Summer’

Hardiness

  • Zone 5
  • Zone 6

See also

Pests and diseases

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