(Editor's Note: This article was originally published on July 30, 2009. Your comments are welcome, but please be aware that authors of previously published article smay not be able to respond to your questions.)
Much of the work involved in finding and developing these new hydrangea cultivars can be attributed to Michael Dirr, retired professor of horticulture and author of several books about woody plants, including Hydrangeas for American Gardens, the most comprehensive book on the subject.
In September, 1998, in a St. Paul, Minnesota wholesale grower's stock, Dirr found a row of Hydrangea macrophylla blooming on the current year's wood, according to Adrian Higgins in the July, 2006 Washington Post article "The Hydrangea That Keeps on Giving." From this discovery, many new cultivars have been developed that extend the range and bloom period of the mophead hydrangeas.
The cultivars are divided into two different groups; the hortensias, informally called mopheads, that have large, showy clusters of sterile blooms and the lacecaps that have flat heads with tiny fertile flowers in the center surrounded by larger-petaled, sterile flowers. Both types are worthy landscape subjects and have graced American gardens for many years.
How are the New Hydrangeas Different?
Up until a few years ago, the bigleaf hydrangeas bloomed only on wood produced during the previous season. Recently, remontant types have been introduced that bloom on both old and new wood, enabling them to bloom over a much longer season. Other free-flowering types reflower from old growth, so the flowering season is extended for this group, as well.
Gardeners in cold regions can more successfully grow the remontant hydrangeas because they bloom even if the summer's growth is killed back by freezing winter temperatures. Gardeners in warmer climates do not fear a late frost that could zap their blooms for the season. Pruning mistakes become less critical since a plant would still bloom, even if the errant gardener cut the shrubs back to the ground in late winter.
All hydrangeas in the lists below are cultivars of Hydrangea macrophylla. Like most of the older members of this group, color is influenced by the alkalinity or acidity of the soil. All are mopheads unless otherwise indicated.
- 'Blushing Bride' - blossoms start out white with blue or pink tints; bred from Endless Summer®
- 'David Ramsey' - hardy to zone 4; compact plant topping out at 4 feet
- 'Decatur Blue' - exceptional hardiness for northern gardeners
- Endless Summer® ‘Bailmer' - the first remontant to be introduced
- 'Mini Penny' - derived from ‘Penny Mac'; very compact
- 'Oak Hill' - similar to Endless Summer
- 'Penny Mac' - from the garden of Penny McHenry (founder of the American Hydrangea Society)
- 'Forever & Ever' - hardy to Zone 4, compact habit growing 3 feet tall and wide
- 'Forever & Ever Double Pink' - compact habit great for small gardens and containers
- 'Forever & Ever Red' - first red-flowering hydrangea, compact habit
Free-flowering Hydrangeas that bloom repeatedly from old wood
- 'Ami Pasquier'
- 'Fugi Waterfall'
- 'Generale Vicomtresse de Vibraye'
- 'Lilacina' (Lacecap)
- 'Mme Emile Mouillere'
- 'Nikko Blue'
While the lists above are not complete, they give a good idea of types available. Breeders continue to cross cultivars, species, and genera to produce more and different kinds. Gardeners look on with anticipation to see what miracles may happen in the world of hydrangeas.
To find out more about hydrangeas, visit the American Hydrangea Society.
Thanks to Rillalev for the image of Endless Summer, to Bootandall for Hydrangea 'Preziosa', and to Soulgardenlove for 'Forever and Ever Pink'.