Some give Martha Stewart the biggest share of the credit for creating an American hydrangea obsession. Serious gardeners, new homeowners and casual flower-lovers, all seem to want the huge, silky blue mop-headed flowers that grace the New England landscape.

The craze pushed breeders back to the drawing board to come up with hydrangeas that would bloom as well in Cleveland as they do in Cape Cod. Further, it’s triggered a procession of new varieties, not only of the ones that could be turned pink or blue, but of other species as well. As Martha always says, “that’s a good thing.”

For hydrangeas that can change color, soil with lower pH allows the plant to more easily absorb aluminum if it is present in the soil. There are two types that are capable of changing color. They are:

Bigleaf Hydrangeas (Hydrangea macrophylla).

This species has very large, somewhat rounded leaves, a trait that gives it the common name, bigleaf hydrangea. The flowers are either mophead (round) or lacecap (flat cluster) in shape. While this species blooms on the previous year’s stems, some varieties are remontant, meaning they also bloom more than once per season and even on current year’s stems. Hydrangea macrophylla are hardy in Zones 5-9 and prefer partial sun.

Flowers on the bigleaf hydrangea can vary from the red to the blue and everything between, depending on the soil in which it is grown. Two factors contribute to plant developing blue flowers—the soil’s pH and the presence of aluminum* in the soil. According to American Scientist magazine’s article by Henry D. Schreiber, for the bluing of hydrangea blossoms, one needs both aluminum ions and acidic soil. He recommends using commercially available aluminum sulfate to change a pink hydrangea to blue. An excellent explanation of soil pH and how it affects plant grown is available from Rodale’s Organic Life.

*Note: Aluminum is one of the most abundant elements on the planet: roughly eight percent of the earth’s mass is made up of aluminum, a chemical element that is not required for plant growth.

The first, and best-known reblooming hydrangea is ‘Endless Summer’, a mophead type. The story of how it came to be is interesting and can be found on the Endless Summer website. Since that introduction, others in that category have followed. Personally, I have some in my northern Indiana garden. They include ‘Let’s Dance Starlight’, ‘Let’s Dance Big Easy’.

Mountain Hydrangea (Hydrangea serrata)

Typically more cold-hardy than Hydrangea macrophylla, but with smaller, mostly lacecap flowers, Hydrangea serrata has been catching on in American gardens. This species from Japan and Korea isn’t as showy as the Bigleaf mopheads. But, they are subject to color change based on soil pH and aluminum content in the soil. They also produce flower buds on side stems as well as the end of the main stems, providing a continual source of color. Hardy from Zones 6-9 (often hardy in Zone 5), it rarely grows taller than four feet. Varieties that I favor:

• ‘Blue Billow’ rarely misses a step in my garden, regardless of winter temperatures. It grows, at most, four feet tall, and the leaves have good red color in the fall.
• The Japanese name, ‘Schichidanka’ is worth learning to pronounce. Its delicate look belies its hardiness, as it has bloomed for the past 16 years in my garden. Its height is perfect (around four feet tall) for close-up viewing of its double lacecap flowers.
• ‘Tiny Tuff Stuff’ is a new variety that reaches just two feet tall and has doubled lacecap flowers. It’s just come through a tough winter seasons yet, and already has flower buds.

Besides the two species that have blue to pink potential, listed below are three others that are worthy of attention for their beauty and no-fuss culture.

Smooth Hydrangea or Annabelle Hydrangea (Hydrangea arborescens)

This American native hydrangea has either lacecap or mophead flowers whose colors cannot be changed. The best new varieties have a more compact stature and stronger stems. Some boast flowers as big as your head, and a few even sport pink flowers.

Hydrangea Arborescens are hardy in Zones 3 -9, prefer full sun to partial shade, and bloom on the current year’s stems. It has fluffy white-flowers and is icon of high summer that goes into a droop after a few rainstorms.

To encourage strong, new growth, and lots of flowers, prune back by one-third its total height in early spring.

• Hydrangea ‘Incrediball’ is true to its name, although it’s best to stake this five-footer, or even surround it with a four-foot wire fence before the stems emerge each spring.
• Hydrangea ‘Invincebelle Mini Mauvette’ has blossoms of the deepest pink. It’s compact, reaching just three to four feet tall, and produces flowers all summer.
• Hydrangea ‘Lime Rickey’. Instead of the fully-round blossoms, ‘Lime Rickey’ has large, disc-like blooms (like the top half of a mophead). They start out a fresh green color and age to rich jade, all accented with pink pollen for a unique accent. It grows up to five feet tall and wide.

 Panicle Hydrangea (Hydrangea paniculata)

One of the easiest hydrangeas to grow, as it blooms on current season’s stems, Hydrangea paniculata flowers start out white and change a rosy pink as they slowly age. Panicle hydrangeas bloom on the current season’s stems, and can be cut back by about one third their height in early spring. Hardy from Zone 3-9, they prefer full sun, but also do well in partial shade. Panicle hydrangea grows anywhere from three to 10 feet. The plant has conical-shaped blossoms that typically contain both fertile and infertile flowers.

One of the most important breakthroughs on this species was the introduction of a variety called ‘Limelight’. Almost as soon as word got out about its huge, bright lettuce-green flowers, this 2006 landscape innovation began winning awards for its stunning presence in the garden.

Since then, several new varieties have come out, but ‘Limelight’ is still one of the best. Smaller stature with sizeable flowers and strong stems are what hybridizers are looking for in panicle hydrangeas. Newest varieties include:

• ‘Bobo’: If you like your hydrangeas smothered in bloom,‘Bobo’ should be your choice. It’s compact, reaching just three feet tall, and its blooms age to a dusky rose.
• ‘Diamond Rouge’: Billed as the reddest panicle Hydrangea, this new variety offers large flowers that turn red earlier than other cultivars on four foot plants.

Oakleaf Hydrangea (Hydrangea quercifolia)

This American native hydrangea makes a statement from mid-summer into fall. With panicles of creamy sterile and fertile flowers that age to rose, it doesn’t stop there. Hydrangea quercifolia’s large, oak-like leaves turn a gorgeous deep red in fall. Hydrangea quercifolia is probably one of the tallest shrubs you can grow; its dwarf varieties top out around three to four feet. It blooms on previous season’s stems, prefers partial shade, and is hardy from Zones 5-9.

Standard varieties, the tallest of which is ‘Alice’, can grow to eight to 10 feet tall. There is a double-flowered form called ‘Snowflake’, which has been a staple in hydrangea-expert Michael Dirr’s Georgia garden. Flowers on this variety look double because of the way its new sepals (infertile flowers) sprout on top of older ones. ‘Snowflake’ grows up to eight feet tall and 10 feet wide.

One of the best, and most compact varieties is ‘Ruby Slippers’, reaching just three to four feet tall.

Conclusion

Whether you’ve had the success of Martha Stewart or have thrown in the towel on the blue Hydrangea, there are so many varieties to add to your landscape that are cold hardy, heat tolerant, and forgiving of untimely pruning, you’re bound to find one (or several) that you’ll fall in love with.

Terminology: 

• Sterile florets – these are the showy flowers that make up the mophead (snowball) form of Hydrangea species macrophylla, arborescens and serrata.
• Fertile flowers – tiny and indistinct, these are more obvious in lacecap type flowers
• Remontant – A remontant Hydrangea is capable of blooming on both old and new wood.
• Old wood vs. new wood – Old wood refers to stem growth from the previous season, while new wood is grown in the current season.
• Mophead – a style of bloom found on hydrangeas that consists of rounded clusters of sterile florets as on ‘Annabelle’ and ‘Endless Summer’.
• Lacecap – flat flower head composed of both sterile and fertile flowers.