H: Thursday, March 27, 2008

Reflections on the Massachusetts Chapter Species Survey

Dick Brooks, Concord, MA

Members of the Chapter have been aware for some time of a project undertaken by the Chapter's Species Study Group. The purpose of that project has been to accumulate information on what rhododendron species are being grown in New England, as well as what species should be possible here but are not yet being grown. To obtain that information, in 1994 the Group started a survey of members who are growing species, using feedback from the periodic Species Profiles which appear in the Chapter newsletter and a questionnaire sent to a number of knowledgeable growers in the area.

Rhododendron vaseyi
Rhododendron vaseyi

The results of that survey to date will be published in a booklet, to be available at the ARS convention in Burlington, MA. The information in that booklet has been gleaned from over fifty members, gardening in the full range of New England hardiness zones, USDA Zones 4A to 7A. A perusal of the data draws one to some interesting and sometimes puzzling conclusions.

For example, of the Group's "master list" of 235 different species rated by various authorities as hardy to -5°F or lower, fully 132 species have been reported as being grown by at least one member. This is a significant number, but the obvious question that arises is, "how about the other 103 species, which should be growable somewhere in New England? Are they lurking as hidden treasures in someone's back forty? Or have they been tried and deemed impossible as garden subjects for our area?" Probably the major reason for the lack of responses is that they are largely unobtainable from commercial sources. A quick check of 39 of the 103 unreported species revealed that only nine were available as plants from the major specialty nurseries, and for these nine most often there was only one source.

One way of overcoming this shortage is by growing these species from seed, and in fact this is a project that has been undertaken by the Chapter's Roundtable Group, with seed obtained from wild collected and hand-pollinated sources from both the ARS and RHS Seed Exchanges.

The Species Study Group has grouped the species reported on, according to the degree of success that may be anticipated by New England gardeners, into four categories:

A—Recommended: plants that are proven reliable performers.

B—Conditionally recommended: plants that may do well for some growers but not for

others or that may require special attention to certain cultural requirements.

C—Not enough data: plants for which there were three or fewer reports.

D—Not recommended: plants that pose a real challenge, even to experienced growers.

In the "A" list it is interesting to note the geographical origins of these "fail-safe" species. Not surprisingly, all of the eastern North American species, except the far southern natives RR. alabamense, austrinum, canescens and flammeum, and the far northern natives RR. canadense, lapponicum and groenlandicum, are represented in this category. The hardy natives of Japan, Korea and eastern Siberia have also proven to be well enough adapted to New England conditions to warrant their inclusion on the "A" list, and the same is true of certain species from central, eastern and northern China: RR. adenopodum, fortunei, micranthum, oreodoxa and sutchuenense.

More surprising, however, is the appearance on the "recommended" list of three Taiwanese species, RR. hyperythrum, nakaharae and pseudochrysanthum, and one from the southwestern Chinese province of Yunnan, R. russatum. The successful cultivation of these raises hopes that many other species from milder climates in southerly latitudes will prove similarly adaptable to New England's climate. Two natives of Europe/Asia Minor round out the "A" list, RR. smirnowii and myrtifolium.

A preponderance of successful reports for many species in the "B" list suggests that with additional input from members some of these might well be relocated to the "A" list of proven performers.

Included in the "C" list are species that were reported on by only one member, yet were obviously successful for that person. These are RR. amagianum, argyrophyllum, campylogynum, haematodes, kiyosumense, mimetes, primuliflorum, pronum, proteoides, ririei, searsiae, tsariense, and wallichii. Why are these not more widely grown? Is it the same problem of limited availability? Or perhaps lack of an adventurous spirit on the part of most of our members?

The eight current members of the Species Study Group were asked to make a list of their favorite species, interpreted to mean the most reliable garden-worthy subjects. The hands-down winner was R. vaseyi, appearing on seven of the eight lists. R. degronianum in its various forms was a close second, with six votes, and a trio consisting of RR. kiusianum, minus and mucronulatum followed with five votes each.

The sixty-page product of the Species Study Group's efforts will be available at the ARS convention in May 2000, for a nominal charge to cover printing costs. Other members will find it a most illuminating source of information, and hopefully will be tempted to try some of the many species covered in the survey.

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