Hydrangea serrata 'Blue Billow'
Mountain Hydrangea
 
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Family: Saxifrage Family (Saxifragaceae)
Native Habitat: Japan

General Hydrangea macrophylla & serrata Info:
Gardeners often lust for plants that are difficult or impossible for them to grow in the region in which they live. Those of us in the mostly alkaline soil mid-west crave Rhododendrons and Azaleas. Southerners wish they could grow Peonies. Most everyone not living in the central U.S. would like to be able to grow sweet corn like we can in the mid-west. Show a Zone 5 gardener catalog pictures of selections of H. macrophylla and a fit of envy and lust is sure to follow.

The vast majority of H. macrophylla varieties (there are over 500) are root hardy in Zone 5 but woefully flower bud tender. They will regrow nicely from the roots after the tops are killed back in winter but produce only foliage; they will not flower. The flower buds that were formed on the last season's stems are usually destroyed by our Zone 5 winters.

Fortunately there are two possible remedies that can ease your Hydrangea macrophylla pain if you live in Zone 5. You can plant one of the few varieties that flower on new wood. Even when they die back to the roots after a northern winter these rebloomers will still bloom. Another option is to plant a selection of H. serrata, a species that is native to the mountains of Japan and is closely related to H. macrophylla but somewhat hardier.

A note on flower color: the pH of the soil in which the plant is grown often determines whether the blooms will be pink or blue. For most H. macrophylla and H. serrata cultivars, blue flowers will be produced in acidic soil (pH 5.5 and lower), whereas neutral to alkaline soils (pH 6.5 and higher) will usually produce pink flowers. Between pH 5.5 and pH 6.5, the flowers will be purple or a mixture of blue and pink flowers will be found on the same plant.

This Variety:
In our gardens, 'Blue Billow' has proven itself to be quite hardy and a very dependable bloomer. We've seen little or no stem die-back in winter. The lace-cap type flower heads have outer sterile flowers colored blue with a overlay flush of pink. The inner fertile flowers are a somewhat darker blue. Since this is a H. serrata variety, the leaves are smaller than in H. macrophylla. It also has excellent fall color. We've also found it to be one of the more adaptable varieties in the H. macrophylla & serrata group. We've grown it for years in very well drained soil in fairly heavy shade, conditions that most others in this group would not like. 'Blue Billow' has shruggged it off and continues to bloom wonderfully each year.

 


 
Ornamental Characteristics: Blue lace-cap type flower heads that stay blue even in neutral soil. Nice maroon fall color.
Habit & Growth Rate: Rapid growth rate to about 3 ft. tall and wide.
Landscape Uses: Shrub border. Mixed border. Foundation plantings.
Hardiness: Zone 5 to 9.
Culture: Best in light to medium shade in moist, well-drained soils.
Awards: Gold Medal Plant Award, Pennsylvania Horticultural Society