Discovering the ‘Bluebird’ Hydrangea Serrata

In 1960, the Royal Horticultural Society honored the ‘Bluebird’ Hydrangea Serrata with the Award of Garden Merit. It is surprising that this wonderful flowering shrub has remained in the shadows for so long. Even one year ago a search on the Internet would find almost nothing on the Serrata at all. This is even more surprising when you consider that every plant that is awarded Award of Garden Merit has been verified to:

• be of outstanding excellence for garden decoration or use
• be available in the trade
• be of good constitution
• require neither highly specialist growing conditions nor care

The specific cultivar ‘Bluebird’ (or ‘Blue Bird’) is an heirloom shrub developed long ago in Japan from a Korean variant, H. serrata forma acuminata, the Mountain Hydrangea. Hydrangea serrata (hy-DRAIN-jah ser-RAY-tah) is perhaps better known by the common name, Mountain Hydrangea or Sawtooth Hydrangea‚Äîif at all. Formerly it was categorized as a Lacecap serrata subspecie of Hydrangea macrophylla because of its flattened flowerheads made up of central, small florets surrounded by showy, larger florets. While the seratta is similiar to H. macrophylla, it is a more compact plant with smaller flowers and leaves and is more cold-hardy than the Bigleaf Hydrangea, among the reasons it has been categorized as its own specie.

The Serrata often remains in the three by four foot range as a mature shrub, but its ten-year size can be as much five or six feet height, & a full six feet width. Although that size does not exactly constitute a small shrub, it is smaller than Bigleaf Hydrangea, hence more suited to smallish gardens. It can over time get bigger still, but as it requires annual pruning to bloom well, the size is easily kept restrained. Importantly, it should be grown in wet or constantly moist, but well-drained soil, but can be grown in sun to partial shade so long as it is sheltered from drying winds and has plenty of moisture.

The Serrata is also treasured because it blooms continuously from June to November and without fail from July through August. And the coloration of its blossoms are unique from others. For instance, the Bluebird’s lacecap is made up of a center of tiny dark blue fertile flowers, surrounded by large sterile petals of palest bluish-purple. It is bluer in acidic soil than alkaline, but it’s fairly blue in any soil condition. It is notable however, that, as insects pollinate the fertile flowers of the center, they turn their petals to reveal pinker reverse side.

Growth rate is moderate to rapid. Pruning can be done for an ideal shape when it is finished flowering in autumn. But pruning to strengthen flowering should be done in late winter or early spring to encourage larger blossoms on established shrubs–prune out 1/3 of the stems cutting at the base of the plant with the choice cuts being defined by the location of fattening buds. The previous years’ flowers which dry on the branches can be left through winter for their own moderate ornamental interest. Deadheading can wait until spring, & at the same time, prune each flowering stem back to the first pair of large buds.

Like most heavy bloomers, the shrub will need regular feeding to bloom its best, a good spring fertilizing minimally & perhaps a couple more times throughout the year.

Full shade may not be the best thing for the Serrata. It will do well in full sun if the soil never dries out. It will do best in partial shade and even become drought-hardy there after its first year.

Foliage turns coppery red to burgundy in autumn. Foliage color is best on shrubs that are positioned in more sun, but flowers fade more prettily in autumn and last longer in dappled sunlight or partial shade.