Breeding a better hydrangea

'Endless Summer' hydrangea                                  Michelle Oshen/Flickr

Hydrangeas are a showy and romantic summer favorite, a shrub ideally laden with flower clusters of classic blue or soft pink that last through much of the season.

If you are still waiting for yours to bloom, you may hit the downside of old-fashioned varieties: Failure to bloom. The “big leaf” Hydrangea macrophylla is the common and familiar kind -- and the one most prone to flower failure. These are broadly divided between “mop heads” with round flower clusters and “lace caps” with blossoms that have a more open flower structure. 

While this plant and its roots are rated for hardiness Zone 6 and higher, which includes most of New Jersey, the flower buds, formed at the end of the season, are vulnerable to frost damage in harsh winters like the one just past. Buds are vulnerable to ill-timed pruning, too, and some homeowners inadvertently lop them off when they cut back their shrubs in late fall or early spring.

On older hydrangea varieties, damaged buds are not replaced and without flowers, hydrangeas aren’t exactly the stuff of landscape excitement.  (Think “big, green meatball.”) I patiently waited six years for my  ’Forever Pink’ hydrangea to bloom – in vain. Finally, in a fit of pique, I dug it up and sent it to the compost heap. Basta!

The tease is that many of the big leaf hydrangeas are exceptionally beautiful and the quest for a spectacular flower display hard to resist. The cure for the flowerless hydrangea blues came in 2001 with introduction of the revolutionary ‘Endless Summer.’  It’s dramatic advance lies in its capacity to bloom on new wood – shoots produced from spring onward – as well as old wood surviving from the previous season.

This meant that the shrub would flower without fail, even if buds were frost damage and even if the stems were killed to the ground by winter freezes. At last, flowers were a sure thing!

Bailey Nurseries of St. Paul, Minn. patented and trademarked this extraordinary find, spotted in a local garden. ‘Endless Summer’ hydrangeas were not only a blockbuster hit, but also spawned breeding programs that have since produced similar reblooming varieties.

Bailey collaborated with Michael Dirr, professor of horticulture at the University of Georgia and author of a dozen essential books on woody ornamentals, to continue research into rebloomers.  Dirr’s hydrangea breeding program shortly produced another reblooming mop head, ‘Blushing Bride,’ which blooms white and matures to a pale pink.

'Endless Summer,' pink on alkaline soils       kkmarals/Flickr

That was in 2007. Since then, the collaboration with Bailey has generated ‘Twist n Shout,’ the first reblooming lace cap with periwinkle blue or deep pink flowers. Another addition is ‘Bloom Struck,’ which bear purplish blossoms leaning toward blue or magenta.

In recent years there has been an explosion in the number of reblooming hydrangeas available for home gardens – and given the weather extremes we’ve experienced lately there’s every good reason to seek them out. Proven Winners has a Let’s Dance series that includes mop heads (‘Big Easy,’ ‘Rave’) and lace caps (‘Diva,’ ‘ Starlight’). Monrovia distributes two lines of rebloomers, the Forever and Ever  and Seaside Serenade series.

If catalogs are a little vague about flower color, it’s because hydrangeas respond to soil chemistry, blooming blue on acid soils and pink on more alkaline ones. Yes, you can mess with your shrubs, pushing for blue with aluminum sulphate compounds or for pink with applications of lime.

Another way to be sure that your hydrangeas will bloom is to choose from other species that are reliably hardy – plant and bud. These, too, are offered in expanding variety as breeders explore their potential.

Hydrangea arborescens or “smooth” hydrangea, once came only in white. Now there’s Invincibelle Spirit from Proven Winners, the first pink. The paniculata group has more cylindrical flower heads and is best known by the very large, very common PeeGee hydrangea. Now there are smaller shrubs with tints of green or pink – 'Little Lamb,' another Proven Winners selection is a fine example.

Finally there is the native oakleaf hydrangea, renowned for fall color as well as summer blossoms. The Gatsby series (again, Proven Winners) includes a pink-flowered variety as well as an incredibly lush white known as 'Moon.'

All hydrangeas enjoy a partly sunny site protected from hot afternoon sun and drying winds. When you realize the root of their name, “hydra” refers to water, you’ll remember that these plants do not like to dry out. Deprived of water, they “wilt like a scolded dog,” in Dirr’s memorable words.

If your hydrangeas have been a disappointment, don’t hesitate to replace them with some of these newer, more reliable varieties. After all, the flowers are the whole point.             

Plant sources

Endless Summer and its relatives -- Bailey Nurseries, choose “Find a Retailer” under “Gardeners” on the home page.

Let’s Dance series from Proven Winners, select “Find a Retailer” from the menu.

Seaside Serenade, Forever and Ever and Gatsby series -- Monrovia, choose “Find a Garden Center” on the home page.