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THE GARDENERS' CHRONICLE OF AMERICA 
THE 
GARDENERS' CHRONICLE 
OF AMERICA. 
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MARTIN C. EBEL, Editor. 
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Vol. XXI 
October, 1917 
No. 10 
CULTURAL NOTES ON RHODODENDRONS 
pERSONS who desire to cultivate these plants must 
remember that Rhododendrons, including all 
Azaleas, cannot live in soil impregnated with lime. 
Rhododendrons are not hardy north of Massachusetts, 
and south of P'ennsylvania the summer sun is too hot for 
them. The range therefore in eastern North America 
where these plants can be successfully cultivated is com- 
paratively small, but probably the northwest coast of 
North America from southern British Columbia to 
northern California is as well suited for these plants as 
any part of the world, and there can be grown in addi- 
tion to all the varieties common in European gardens 
the Himalayan and Chinese species which here in the 
east can only be kept alive in glass houses, and in Europe 
thrive only in a few exceptionally favorable places like 
Cornwall or in the neighborhood of the Italian lakes. 
Rhododendrons, although they are moisture-loving 
plants, do not thrive in undrained positions ; they do 
best in soil in which loam and peat have been equally 
mixed, although peat is not always essential to the suc- 
cessful cultivation of these plants. They should be 
planted where the roots of trees cannot take away moist- 
ure from them, and the best position for these plants is 
on the north side but not too near coniferous trees, as 
they are planted in the Arboretum. In such positions 
they are protected from the direct rays of the sun in 
March and April, for in this climate where the roots are 
in frozen ground in winter and therefore cannot take up 
moisture, it is important to reduce as much as possible 
winter and early spring evaporation from the leaves. It 
is this evaporation from the leaves of evergreens grow- 
ing in frozen soil which makes it impossible to keep alive 
many of them in this country ; and this is the reason why 
it is desirable here to water thoroughly Rhododendrons 
just before the ground freezes in the autumn. Rhodo- 
dendrons imported from Europe suf¥er here from the 
stock on which they have been grafted. The almost 
universal custom among European nurserymen is to use 
Rhododendron poiiticuin as the stock for these plants 
because it is easily and quickly raised and readily grafted. 
R. ponticum is not at all hardy here, and there is little 
doubt that our want of success with Rhododendrons im- 
ported from Europe is due, in part at least, to the stock 
on which they have been grafted and that the gradual 
or sudden death here of large plants which have been 
uninjured by cold or drought for twenty or thirty years 
is due to this cause. 
The familiar Rhododendrons of New England gardens 
are so-called Catawbiense Hybrids and were raised in 
Europe many years ago by crossing R. catazvbiense, a 
native of the highest summits of the Appalachian Alount- 
ains, with Himalayan species, notably the scarlet-flowered 
R. arboremn. It might be expected that plants obtained 
from these crosses would be hardly in proportion to the 
predominance of the American plant but, judging by the 
color of the flowers, this is not always true. Varieties 
like Atrosanguineum, Charles Dickens and H. W. Sar- 
gent, which have flowers as bright red as those of R. 
arboreum, are among the hardiest of all garden Rhodo- 
dendrons ; but varieties with white or pale flowers are 
more tender than those with rose pink of purple flowers 
which most closely show the influence of the Cataw- 
biense parent; and unfortunately the varieties with 
light-colored flowers marked at the base with large 
brown or chocolate-colored blotches, like Sapho, are 
not at all hardy here. 
The hardiness of these hybrid Rhododendrons can only 
be determined by trial, although in selecting varieties for 
trial is is safe to assume that plants with broad leaves 
resembling those of R. catawbilnse, like Everestianum, 
Mrs. C. S. Sargent, Roseum elegans, Henrietta Sargent, 
Catawbiense album, and all the varieties with light or 
dark purple flowers are likely to prove hardier than the 
plants with narrow leaves like j\Irs. John Clutton. There 
are, of course, exceptions to such a rule. For example. 
Pink Pearl has broad leaves and is very tender ; and 
Comer Waterer, although it has leaves as broad as those 
of any of these hybrids, usually suft'ers in winter and 
almost invariably loses its flower-buds. 
Persons who want to plan Catawbiense Hybrid Rho- 
dodendrons should take advantage of the knowledge 
which has been laboriously and expensively obtained 
about these plants at Wellesley on Mr. Hunnewell's 
estate, where Rhododendrons have been tested on a large 
scale for sixty years, and here at the Arboretum where 
many of the hardiest kinds raised in England, Germany, 
and the United States will now soon be in flower. 
There are other evergreen Rhododendrons which are 
not as often cultivated here in INIassachusetts as they 
might be. R. catazvbiense itself is perfectly hardy and 
none of its hybrids have handsomer foliage. It grows 
slowly, however, and never to a very large size, and the 
flowers are of a disagreeable purple rose color. 
Rhododendron m.\ximum, which grows naturally as 
far north as southern New Hampshire, is a large plant 
sometimes treelike in habit, with handsome, long, narrow 
leaves and small clusters of beautiful pink and white 
fldwers. It is the last of the Rhododendrons to bloom 
here, and the flower-buds do not open until the new 
branchlets have nearly finished their growth, so that the 
flower-clusters are a good deal hidden by them. 
The varieties and hybrids of the dwarf Rhododendron 
caiicasiciiin bloom before the Catawbiense Hybrids, and 
the flowers have already faded. The latest of this race 
to flower, and perhaps the best of them all here, is a 
low, broad, compact plant with pure white flowers called 
Boule de Neige. This is a perfectly hardy, free-flower- 
ing plant which might to advantage be more generallv 
planted in Massachusetts. — Arnold Arboretum Bulletin. 
