Loco Weeds, Their Sunny Side
Edward S. Rothman, Glenside, PA
Austin Kennell's article in the Winter '84 issue of the Journal requires some comment before commerce between the rhododendron growers of the Pacific Northwest (N.W.) and the Northeastern USA (N.E.) is brought to a grinding halt. There was a smudge on my copy at the point where "in loco suo" was translated. Perhaps the reading should follow the Spanish to imply that some rhodos are plumb loco. Considering how many variables are involved in the biochemistry of living things, information from multiple sources should be de rigeur before reaching too hasty conclusions.
I have been obtaining plants from the N.W. for a few years now especially those from the heartland of rhododendron eugenics in Oregon and in mulling over the effects of "plant introduction" from such remote areas have come up with some hasty conclusions of my own that I would like to share.
In a guidebook for the perplexed grower published in the N.W. I note color photographs of well known "Spring Glory" and "Cosmopolitan" showing color saturation unknown on the same clones grown in the Philadelphia area where our flowers seem laundered with a bit too much hypochlorite bleach. The reverse effects namely the transduction of Eastern clones to the N.W. I can infer only indirectly. The N.E. mainstay Dexter hybrids are scarcely listed in N.W. sales offerings, apart from 'Scintillation' and 'Gigi'. Have they never heard of 'Bass River' or 'True Treasure' or 'Helen Everitt'? Perhaps these do not acclimate as well out west?? On further reverse discrimination 'Wheatley' and the unimpressive 'Wissahickon' are listed as "considered to be one of the best in the East" or "has a very good reputation in the East".
Leach, in his "Rhododendrons of the World" has indicated differences in the amount of light annually delivered to plants in the N.W. as compared with the N.E. in terms, e.g., of average number of overcast days and shows that "full exposure" on one seaboard does not mean the same thing as full exposure on the other seaboard. But one remembers how high-elevation Asiatic plants have adjusted to low elevation living at very different latitudes and looks for other effects in transcontinental comparisons. R. yakushimanum from treeless 30th parallel Yaku Shima and R. pseudochrysanthum from Taiwan heights are perfectly happy both in the N.E. and the N.W. The explanation is not in the indumentum for R. roxieanum and even R. globigerum fare far less well.
Factors to weigh on the balance pan are not only hardiness of floral bud, but summer heat tolerance, pathogenic mold susceptibility, (allowing a plant that has happily weathered zero weather to topple over on a balmy summer day), and the nature of the growing medium. It is common experience to find a cast iron hybrid rated at -30 degrees F. with burned leaves, whereas in the same garden a 0 degree F. relatively delicate plants come through "clean as a whistle". Sometimes the explanation is as simple as choice of site. The fellow with coniferous backgrounds for his rhododendrons has a great advantage over the fellow with a heavy screen of oaks or maples which are leafless in winter such that reflected glare bouncing off polished ice snow sheets is baffled.
Winter shading can be quite important. Here, even camellias and the tea plant C. sinensis (formerly Thea sinensis) "make it" regardless of whether winter temperature minimum is +20F (1983 winter) or -7F (1984 winter) provided the plants see no trace of direct winter sunshine.
Some N.W. plants suffer from winter sun, e.g., 'El Camino', but so do some N.E. hardy Shammarellos like 'Yaku Prince' even though its five siblings like plenty of open sunshine, even winter sunshine. But many of the N.W. "introductions" which came as young plants for April delivery by air express are quite at home in my garden when kept out of winter sun. Against all advice I have put in some borderline hardy plants like 'Sue' = 'Loderi King George' selfed, 'Loder's White', a 'Walloper', 'Halfdan Lem' R. orbiculare 'Anna Rose Whitney' and Greer's unidentified R. adenophorum affinity; they all are doing fine. But don't try to grow mold susceptible R. souliei or wardii or bureavii in forestry woodland here in Philadelphia's humid summer even though they can survive the winters easily.
In this climate it is important to allow proper time to lapse for hardening off prior to winter. This even applies to seedlings planted in early January so that they can be put outdoors in June or July to fend for themselves under the snow with a wire gauge (or jar) to protect them from birds and squirrels. The ARS seed distribution in February comes a bit too late for optimum timing but they yield golden harvest.