JARS v44n1 - Heritage Plantation's New Hybrids: The Cowles Plants Come Of Age

Heritage Plantation's New Hybrids: The Cowles Plants Come Of Age
Jonathan Leonard
Sandwich, Massachusetts

Heritage Plantation is magnificent. Many consider its immense rhododendron gardens to be the finest on this side of the Atlantic. But Heritage also seems outpaced by the theme of the 1990 American Rhododendron Society Convention, "Rhododendrons for the 1990s, The New England Perspective," because its gardens are not new. Indeed, Charles Dexter hybridized his plants there in the 1920s and 30s; well over a hundred of his spectacular cultivars have already been named; and so the Heritage gardens appear unlikely to offer much that is novel or unknown.
Appearances, however, can be deceiving. The truth is that most of the rhododendron hybrids at Heritage are not Dexter's. They were created much more recently by a horticulturist named Jack Cowles (pronounced "coals") who used Dexter's methods and plants, together with pollen from a wide range of interesting parents, to populate large available expanses of the former estate with rhododendron seedlings. Currently 20 to 30 years old and in their prime, those seedlings constitute one of the most massive hybrid rhododendron plantings in the world. Largely unnamed and unevaluated, they have recently attracted increasing attention from rare plant connoisseurs and now seem poised to make a major contribution to "Rhododendrons for the 1990s" and beyond.
This state of affairs, the horticultural equivalent of finding someone other than Grant buried in Grant's Tomb, demands an explanation. But in fact the circumstances are not all that bizarre and indeed the situation seems quite logical in light of the Dexter Estate's past.
When Charles Dexter hybridized his rhododendrons at the present site of Heritage Plantation, he named none of his seedlings and shipped multitudes away. As a result, when he died in 1943 his plants were widely scattered. To evaluate them, a committee of rhododendron experts had to visit places they had gone. The committee did visit Dexter's former home and found whole hillsides blooming; but early efforts to take and root cuttings from this site ran into problems, and so most of the ultimately evaluated and named Dexters came from outside the present Heritage Plantation grounds.
From 1945 until 1959 the estate passed through four sets of hands, and Dexter's plants fell upon hard times. Many were sold, given away, or carried off by the owners when those owners departed the estate. The fiercest depopulation happened in the 1950s - after a land developer bought the property, failed in his attempt to split it up, and thereupon sold off thousands of plants for whatever he could get.
Other troubles also confronted the plants Dexter had brought in and those he had created. Native trees and shrubs encroached; and while these could be cut back, there was no easy way to deal with crowding within large plantings. So competition and disease took their toll in a slow process of growth, aging, and elimination that has continued to the present.

In 1959 Jack Cowles and his wife Eveleth (also a horticulturist) were hired by the estate's owners, Stanley and Robert Berns, to make improvements. They discovered that despite previous depredations a surprising amount of fine plant material had survived. So they enthusiastically identified and evaluated it, as Eveleth explains in her book The Dexter Estate: Its Gardens and Gardeners . They also named and registered certain hybrids that seemed especially promising (including 'Dexter's Giant Red', 'Dexter's Orange', 'Dexter's Springtime', 'Dexter's Victoria', and 'Dexter's Spice'), and began propagating and circulating these hybrids. In addition, Jack embarked on a mammoth breeding program of his own, using the plants on the estate together with pollen and plant material from many sources, in order to continue Dexter's work, repopulate vacant parts of the estate, and produce new plants of merit.
If anything, this breeding program was too successful. When I worked for Jack briefly in the early 1960s, as a college kid providing incidental summer help, the place was a swarm with seedlings. So numerous were they that they clearly exceeded the available capacity to tend them, and I seriously wondered how many would survive - a concern that proved unwarranted.
In 1967 the property was sold, Jack and Eveleth departed, and Heritage Plantation was established. By then vast numbers of those seedlings had been planted - in backland tracts of oak and pine as well as in more civilized parts of the estate. And even though the construction of Heritage removed some of them, a mighty throng remained.

Not all the members of this throng were actually Jack's creations. He sometimes imported seed, such as the open pollinated R. wardii seed from England that apparently gave rise to several handsome but marginally hardy yellows designated Heritage #408/971. He also took scions and made grafts, most notably of certain stunning Consolini ¹ bi-colors, one of which was recently introduced as 'Consolini's Windmill'. By and large, however, the seedlings came from his own crosses. Many were beautiful, as the pictures on these pages attest. And in time, over 20 years or so, they came of age.
The first person to recognize and effectively publicize this fact was Ed Collins, an ARS District Director from New Jersey who occasionally visited the site. While driving past Heritage one day he spotted some color in what looked like native woods and investigated. He discovered thousands of rhododendrons, some over twelve feet tall, growing on Heritage land in a pineoak wilderness among impressive stands of bull briar and poison ivy. Possessing an intrepid streak, Ed decided to explore these wilds. So he located promising plants, took pictures, informed Heritage Plantation and local rhododendron enthusiasts about his work, and enlisted their support in propagating and evaluating what he found.

One thing this work brought out was that like the Heritage woods, the Plantation's manicured grounds also harbored thousands of seedlings 20 to 30 years old, which because of uncertainty about their origins had become known as "Heritage hybrids." A few of these had been arranged in coherent plantings by Heman Howard, the horticulturist who succeeded Jack Cowles; but most remained where Jack had put them. Even so, as they grew, and as Dexter's surviving plants declined, they came to dominate the scene.

This only dawned on me last May, when we were planning the 1990 American Rhododendron Society Convention garden tours at Heritage. Besides guiding visitors through the Dexter Display Garden (a concentrated collection of named Dexter hybrids brought back to Heritage by Heman Howard in the 1970s), we planned two kinds of tours - one of Dexter's original plants and one of the Cowles hybrids. We found this approach unworkable because there were too few interesting Dexter plants in any single limited area to provide the basis for a one hour walking tour. In contrast, the Cowles plants were legion, with plenty of promising ones close together. So we combined the tours and reached the obvious conclusion that Jack's seedlings had become the mainspring of the vast Heritage display.

None of this need detract from Charles Dexter's rhododendrons. Despite severe attrition, a good number of Dexter's original plantings and creations have survived, and Heman Howard's more recent five acre Dexter Display Garden now holds the best concentrated collection of named Dexter hybrids in the world. Furthermore, we are still learning new things about the Dexters (see Jon Valigorsky's article on Dexter hardiness in the last issue, ARS Journal Vol. 43:4, for example); and these plants offer so much to collectors, breeders, and landscapers alike that they are well worth visiting.
Seen in this light, the Cowles hybrids are simply a stupendous bonus. What makes them so exciting is their future. Evaluation has just started; and while it is too early to tell how they will fare, it seems likely that important new plants will emerge. In terms of the 1990s, then, these predominant plants at Heritage are quite in tune with the forthcoming ARS National Convention and its theme; for real awareness of them is just dawning, and their time has still to come.

¹ Anthony Consolini was Mr. Dexter's head gardener and a hybridizer in his own right.

Jonathan Leonard is the proprietor of Briarwood Gardens, a nursery in East Sandwich, Massachusetts, specializing in the Dexter hybrids.