Plant taxonomy classifies the plant described below as Hydrangea macrophylla 'Nikko Blue.' Macrophylla is the species name and signifies "big leaf"; thus you will hear the classification "bigleaf hydrangea." 'Nikko Blue' is the cultivar name.
These bushes are deciduous flowering shrubs. They are 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 the Shrub, and What "Sepals" Means
H. macrophylla 'Nikko Blue' grows to be at most 4-6 feet tall, with a similar spread. The more shade the bush receives, the shorter it may remain; in extreme cases, the plant may stay short enough to resemble a large perennial in size. The 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 are blue hydrangeas, flower color really depends on soil pH (see below under Changing Blue Hydrangeas Pink).
Planting Zones, Sun and Soil Requirements
Nikko Blue is sometimes listed for growing in planting zones 6-9, but it can even be successfully grown in zone 5 without providing mulch for it 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.
Nikko Blue requires an average amount of watering. Grow it in partial shade and in a loamy, well-drained soil enriched with compost. Morning sun and afternoon shade is often recommended as a rule of thumb, although gardeners in 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, Care (Pruning)
A popular shrub for use in the cottage garden style, these hydrangea bushes 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 others are indifferent to it.
Nikko Blue hydrangea bushes do not require much (if any) pruning, but the main thing that you need to know if you do feel compelled to prune them is that they bloom on old wood. Buds are set in late summer to early fall, so prune prior to this. 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 (Endless Summer, Etc.)
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.
- H. macrophylla 'Mariesii Perfecta' (aka Blue Wave) is one of the better known lacecap varieties (zones 5-9).
Endless Summer may well be the most popular of them all. It grows to a height of 3-4 feet, with a similar spread. This repeat bloomer gets its name from the fact that it provides vibrant color for a longer span of time during the summer than most: July to September. As with Nikko Blue, the flower color may be blue or pink, depending on your soil (see below). But unlike with Nikko Blue, blooming occurs on both old and new wood, so you have more leeway with pruning. All types of bigleaf hydrangeas are poisonous plants, so you must be vigilant while growing them if small children will be running around in your landscaping.
Changing Blue Hydrangeas Pink and Vice Versa
These bushes will bear blue flowers in acid soils, but pink blooms in alkaline ground. If a soil test reveals insufficient acidity and you desire a blue color, just raise acidity. Happily, it is very easy to change a bigleaf hydrangea's color to either pink or blue, depending upon what you want it to be.