Complimentary 
NEW SERIES VOL. Ill 
NO. 9 
ARNOLD ARBORETUM 
HARVARD UNIVERSITY 
BULLETIN 
OF 
POPULAR INFORMATION 
JAMAICA PLAIN. MASS. JUNE 20. 1917 
Rhododendrons. The flowering of the principal Rhododendrons in the 
collection is very late this year but the plants are in an unusually good 
condition and many varieties will be in bloom this week. Persons who 
desire to cultivate these plants must remember that Rhododendrons, 
including all Azaleas, cannot live in soil impregnated with lime. Rho- 
dodendrons are not hardy north of Massachusetts, and south of Penn- 
sylvania the summer sun is too hot for them. The range therefore in 
eastern North America where these plants can be successfully culti- 
vated is comparatively 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 addition 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 successful cultivation of these plants. They should be planted 
where the roots of trees cannot take away moisture 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 re- 
duce as much as possible winter and early spring evaporation from the 
leaves. It is this evaporation from the leaves of evergreens growing 
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