Hydrangea macrophylla 'Penny Mac'
Bigleaf 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:
'Penny Mac' is named for the founder of the American Hydrangea Society, Penny McHenry. One of the select varieties that blooms on new wood, it blooms like crazy all summer even if your plants were killed back to the ground last winter. The 7" flower clusters are usually pink here in the mid-west, but will be blue if you acidify your soil by adding aluminum sulfate.


'Penny Mac' grown in acid soil
'Penny Mac' grown in neutral or alkaline soil
Ornamental Characteristics: Summer bloomer beginning in July and blooming well into fall. Pink flowers in alkaline or neutral soil. Blue flowers in acid soil.
Habit & Growth Rate: Rapid growth rate. Will grow up to 5 ft. in the south but usually only 2 to 3 ft. in the north where they are usually killed back to the roots in most winters.
Landscape Uses: Shrub border. Mixed border. Foundation plantings.
Hardiness: Zone 5 to 9.
Culture: Full sun to light shade. Best in moist, well-drained soils. Adequate moisture is important.