Plant Taxonomy of Nikko Blue Hydrangeas:

Plant taxonomy classifies the blue hydrangeas with which I deal here as Hydrangea macrophylla 'Nikko Blue.' Macrophylla is the specific epithet and signifies "big leaf"; thus you will hear the classification "bigleaf hydrangea." 'Nikko Blue' is the cultivar name.

Plant Type:

These bushes are deciduous flowering shrubs. Classified as being in the "mophead," or "hortensia" group.

The "mopheads" are so called because they produce large balls of sepals (see below). By contrast, the "lacecap" type displays a flatter flower head, with the sepals aligned more around the perimeter, surrounding the tiny, fertile blooms in the center.

Characteristics of Nikko Blue Hydrangeas:

H. macrophylla 'Nikko Blue' grows to be 4-6 feet tall with a similar spread. Shrubs are multi-stemmed and grow in an upright habit.

When we speak of the "flowers" of this shrub, we have to be careful, if we wish to be technically accurate. The showy parts are actually not flowers, but rather sepals -- tough, bract-like structures that persist for months. The "flower" clusters usually first appear in July. Despite bearing a cultivar name indicating that they'e blue hydrangeas, flower color really depends on soil pH (see below under Changing Blue Hydrangeas).

Planting Zones for Nikko Blue Hydrangeas:

Sometimes listed for growing planting zones 6-9, but I've successfully grown mine in zone 5 without providing mulch for it specifically and without applying a tree wrap for winter protection.

However, many have reported problems with bud loss due to cold winter weather, so wrapping with burlap is often advised. These bushes are indigenous to the Far East.

Sun and soil requirements for Nikko Blue Hydrangeas:

Requires an average amount of watering. Grow in partial shade and in a loamy, well-drained soil enriched with humus. Morning sun and afternoon shade is often recommended as a rule of thumb, although denizens of the South may wish to furnish more shade, while those who live in cooler climates may get away with a location in full sun.

Uses in Landscaping:

A popular shrub for use in the cottage garden style, these blue hydrangeas are attractive enough to use as specimen plants when in full color, during the summer. They are sometimes planted en masse along a property border or included in a foundation planting. Because they consist mainly of sepals, the flower heads persist through fall (although the color will fade), adding interest to the autumn landscape; they can be harvested for dried arrangements. Some growers prize the foliage, but I'm indifferent to it.

Care: Pruning:

H. macrophylla 'Nikko Blue' blooms on old wood. Buds are set in late summer to early fall, so prune prior to this (if you feel you have to prune at all). If you prune after the buds have been set, you risk losing flowers for next year (but, as always, dead branches can be pruned out at any time). Prune back to where you see healthy buds growing.

Other Types of H. Macrophylla:

H. macrophylla is said to be the most popular hydrangea shrub. There are many types of H. macrophylla beyond the one covered in this article; for example:

• H. macrophylla 'Endless Summer,' so called because it is a repeat bloomer; it is also valued for its hardiness (zones 4-9).
• H. macrophylla 'Variegata' exhibits variegated leaves (zones 5-9) and lacecap flowers.
• Hydrangea macrophylla 'Mariesii Perfecta' (aka Blue Wave) is one of the better known lacecap varieties (zones 5-9).

All types are toxic. View my pictures of poisonous plants for other plants you must beware of if small children will be running around your landscaping.

Changing Blue Hydrangeas Pink and Vice Versa:

These bushes will bear blue flowers in acid soils, but pink in alkaline ground. If a soil test reveals insufficient acidity and you desire a blue color, just raise acidity. In an article on another type of H. macrophylla, I discuss how to change a hydrangea's color at greater length.