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GARDENING

Four hydrangeas give hope to Boston gardeners in a blue mood

Hydrangeas are the most happening and hyped plant in the gardening world. And for Boston gardeners they are also the most frustrating. I get more questions about hydrangeas than any other shrub. How can I turn the flowers blue? How do I prune it? And, most of all, why doesn't it bloom?

It started when Martha Stewart sang the hydrangea's praises in the early 1990s as a shade-tolerant shrub that bloomed through the hammock days of summer, and could also be cut and dried for wreaths and other glue-gun projects. Best of all, the flowers were (sometimes) true blue, the most-sought garden color.

Gardeners rushed out and bought blue hydrangeas by the millions. One wholesale grower reported selling 10,000 in one day after Stewart did a TV show on these old-fashioned plants.

It sounded like a good thing.

But the blue mophead hydrangeas that everyone wanted were not hardy in Boston. Well, the shrubs were hardy, but the flower buds freeze-dried over the winter. It didn't take much to kill them this far north, just an early fall frost or a late spring frost would do it.

This proved worse than having the shrub die outright. Every year people would look at their apparently flourishing hydrangeas and wonder why Martha's had flowers and theirs didn't. And to add to the confusion, some years some would actually bloom. Usually the neighbor's. In short, blue hydrangeas in Boston were a tease that drove people crazy.

Meanwhile, people living on the Cape or the coast, where winters are gentler and summers are cooler, had just fabulous blue hydrangeas. But they had another problem, too. Thanks to Martha's magic, the big blue balls became hot as cut flowers, too, commanding $5 per stem, and hydrangea rustling commenced. Cape Cod police blotters recorded thousands of front-yard flower heads decapitated in the middle of the night by thieves who snipped the truest and bluest, often leaving the mauvy-pinks behind.

It was all too aggravating. I was at the point of telling local readers to just forget about hydrangeas. Or at least the social-climbing blue ones. Four handsome hydrangea species do bloom reliably through most of New England: the huge flowered Annabelle and other Hydrangea arborescens, the tree-like PeeGee hydrangea (H. paniculata), the very shade-tolerant native oakleaf hydrangea (H. quercifolia), and the climbing hydrangea (H. anomala), the best blooming vine for shade. Sounds great. So what's the problem? They all have white flowers.

But now there's good news for gardeners bent on blues. Plant breeders and nurseries are responding to the demand by rushing new and improved varieties to the marketplace, including some blue hydrangeas that will bloom reliably in Boston and most of New England.

It's hard to overstate the horticultural fanfare accompanying Endless Summer, the first such blue mophead (H. macrophylla). Almost 2 million have been sold this year so far. It really is new and different. Though it has flower buds that can die over the winter, it will also produce new buds that bloom the same year. This is called blooming on new wood. It also has the ability to rebloom after flowers are cut. Solace for the rustled?

Endless Summer has been called a breeding breakthrough, but actually it's the rediscovery of an old variety. Vern Black of the giant wholesaler Bailey Nurseries Inc., in St. Paul, found it blooming miraculously in his neighbor's yard after a typically harsh Minnesota winter and took cuttings from the plant to the nursery for propagation. There Michael Dirr, one of the country's leading horticulturists, spotted it. He trialed it at his hydrangea-breeding program at the University of Georgia and proclaimed it the bloomingest hydrangea ever. Bailey quickly patented it and began reaping profits nationwide.

It turns out that Endless Summer is not unique, however. Other gardeners started telling Dirr about old blue hydrangeas they had in their backyards that re-bloomed on new wood, and the professor started building a collection. He suspected they were all the same cultivar, a long-forgotten greenhouse pot plant that been once sold throughout the country and was now simply showing up in different locations. But a DNA analysis revealed that while one of the hydrangeas, named David Ramsey after its backyard owner, is similar to Endless Summer, the others, dubbed Decatur Blue, Oak Hill, and Penny Mac, are genetically different. But they all look alike: 4-foot shrubs that produce large quantities of flower balls that are blue in acid soil and pink in alkaline soil, and that rebloom over many months.

So if you are looking for a blue hydrangea that blooms in Boston, any of these will do. And the unpatented ones will probably be cheaper. "Nothing matches these for quantity of flowers," said Dirr. "It's exciting to tell someone in New England that we have a hydrangea that will bloom for you." Dirr is using these genes in his university's breeding program and predicts that reblooming hydrangeas will make older varieties obsolete, especially in the North.

Endless Summer is carried by most major nurseries, including Mahoney's at seven locations, (781-729-5900, mahoneysgarden .com), Kennedy's Country Gardens, Route 3A, Scituate (781-545-1266, kennedyscountrygardens.com) and Briggs Nursery, Route 152, North Attleborough (508-699-7421, briggsgarden.com). It's a good idea to call ahead to reserve one. "I haven't seen so much excitement and demand for a plant before," said nurseryman Gary Briggs. A few nurseries also carry Penny Mac, named after Penny MacHenry, who founded the American Hydrangea Society a decade ago. (A plant has truly arrived when it has its own society.)

Nantucket Hydrangeas, 86 Madaket Road, Nantucket Island, (508-228-2649, nantuckethydrangea.com) the northernmost nursery specializing in hydrangeas, does most of its business via mail order and sells all five known reblooming blue mophead varieties, plus 200 more types. Nantucket Hydrangeas' Frank Dutra also recommends mountain serratas, a strain of blue lacecap hydrangeas imported a decade ago from Japan. Their flower buds are formed the previous year and they don't bloom on new wood, but Blue Billow is blooming in Newton now and you might also try Little Geisha, Tokyo Delight, Blue Bird, and Blue Deckle.

Prune a third of the stems of mophead hydrangeas (H. macrophylla) to the ground after blooming and cut off flower heads when they become tattered. But do not prune the flowerless straight shoots without side branches because these are the ones that will branch out and flower next year.

Annabelle is a cold, hardy white H. arborescen that blooms better if cut entirely to the ground in late winter. Oakleaf hydrangeas and paniculata hydrangeas do not need pruning.

If your hydrangeas are pink and you want them to be blue, or bluer, increase the acidity of the soil. To make them pinker, scatter lime.

This doesn't work for white-flowered species, but there are ongoing attempts to change their colors through breeding. Dirr's Amethyst is an oakleaf hydrangea whose flowers mature from white to red.

Chantilly Lace is an H. paniculata introduction by Dirr's University of Georgia breeding program, which evaluated 20,000 hydrangea seedlings from several species to select 10 new introductions. Dirr's Lady in Red lacecap hydrangea will soon be featured at The Home Depot. And the Georgia professor has plenty more in the pipeline. "I'm in search of the perfect hydrangea," he said.

For more about hydrangeas, see Dirr's excellent new book "Hydrangeas for American Gardens" ($29.95, timberpress.com), the only up-to-date book about the subject. There's also a CD-ROM of 900 Dirr photos of the newest and best hydrangea cultivars ($34.95 at varsity-press.com). They're luscious but don't get too excited if you live in Boston. Most of them won't bloom here.

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