Excerpt of "Reblooming Hydrangeas"  by Richard E. Bir
The identification of bigleaf hydrangea cultivars that rebloom reliably will mean gardeners no longer have to suffer through hydrangea envy.

No doubt you have visited or seen pictures of gardens where stunning flowers of bigleaf hydrangeas (Hydrangea macrophylla) are on display. They may be blue, purple, soft shell pink, hot pink, reddish, ivory, or white. No matter the color, in full bloom, bigleaf hydrangeas are the superstars of the summer garden, capable of stopping gardeners and passersby dead in their tracks.

But while they can be truly spectacular during their period of summer bloom, for those of us who’ve grown one that failed to bloom or bloomed for just a short period, they can be equally as frustrating. Hydrangea bloom failure has many potential causes (see page 36), but most commonly it happens because flower buds were killed by late spring frosts or were lost when stems were pruned at the wrong time.

For the hydrangea-challenged, help is on the way in the form of selections that rebloom reliably even in the face of ill-timed pruning or the vagaries of early spring weather. Unlike standard bigleaf hydrangeas, these plants are truly remontant, or reblooming, producing new flower buds all season long rather than just in late summer.

TRIAL AND ERROR

The discovery of these reblooming hydrangeas can be traced to research that began a decade or so ago. At that time, hydrangeas had gone from being grandma’s old porch plants to cutting-edge novelties in that infinite cycle of plant popularity that garden historians remind us about whenever we think we have discovered something new.

In response to the surge in popularity, some horticultural researchers decided to sort out which hydrangeas were best. Trials of hundreds of cultivars were established at several sites around the United States, including where I work at North Carolina State University’s Fletcher research station, and at the University of Georgia, where Jeff Adkins oversaw trials under the direction of woody plant guru Michael Dirr. The most exciting—if somewhat unexpected—outcome of this research was the discovery that some cultivars are truly remontant.

During trials in Fletcher, where we enjoy the mild climate of the North Carolina mountains, we discovered to our surprise that some hydrangea cultivars were killed to the ground over the winter yet still produced flowers the same summer. Our first instinct was to try to rationalize this finding based on prevailing wisdom, and indeed we recognized that some of these plants were probably insulated by mulch. However, for some cultivars, this explanation did not work, and we were forced to take a closer look and keep better records.

Subsequently, we identified a number of cultivars that produced new flower buds all season long (see box, “Dependable Rebloomers,” page 33). Unlike other bigleaf hydrangeas, the flower buds on these cultivars did not require exposure to winter chilling in order to flower. This suggested that these cultivars were truly remontant. Perhaps the most promising of these selections is Endless Summer™ (its cultivar name is ‘Bailmer’), a selection initially spotted by Michael Dirr in 1998 growing in trial plots at Bailey Nursery, a wholesale company in St. Paul, Minnesota. Hardy to USDA Zone 5, Endless Summer™ has pink to blue flowers, depending on soil pH. This promising new plant has been introduced by Bailey and is scheduled to become widely available in spring 2004.

Opportunistic Bloomers

In the course of our study, we observed another group of cultivars that flowered at the normal time of June in the mountains of North Carolina and were also in bloom with new flowers forming and opening in September….

The photo shows Hydrangea Endless Summer.
Photo courtesy of Bailey Nurseries.
Click on image for larger version


AHS members can view this article in its entirety by clicking here.