HARDINESS: The American Rhododendron Society has recently es- 
tablished a scale of hardiness ratings based on the minimum 
temperatures which the varieties as dormant plants may be ex: 
pected to withstand with no appreciable injury to leaf, stem or 
bud. Of course, in addition to actual varietal resistance to cold 
other factors affect the ability of any individual plant to escape 
injury, such as length of exposure to low temperatures, rate of 
temperature fall, extent of dormancy, protection from wind, ex- 
posure to the sun, and the growth condition of the plant as af- 
fected by age, previous flowering, fertilizers used and the condi- 
tion of the graft union. The A.R.S. hardiness ratings are as fol- 
lows: H-1—Varieties hardy to -25°F. These varieties should be 
hardy in southern New York and southern New England. H-2-—- 
Hardy to -15°F. H-3—Hardy to -5°F. These varieties should be 
fairly hardy in the southern part of Long Island and around 
Philadelphia. H-4—Hardy to +9°F. — H-5—Hardy to +195°F. 
These varieties should be hardy during most winters in the Port- 
land and Seattle areas. H-6—Hardy to +29°F. H-7—Hardy to 
+32°F. 
The winter of 1949-50 was especially severe in the Pacific 
Northwest, certain well-known Rhododendron gardens exper- 
iencing temperatures as low as -18°F. This presented an unus- 
ually fine opportunity to secure data from many growers on 
which to base tentative American hardiness ratings. These rat- 
ings, as published in the October, 1950 Bulletin of the American 
Rhododendron Society, are used in this list. It is significant that 
very few varieties were reported as actually killed at -18°F. 
Some were severely injured and others were killed to the ground 
but later sprouted up again. This would seem to indicate the 
advisability of having varieties on their own roots where winters 
are severe, aS any shoots sent up by grafted plants, if killed to 
the ground, would be from seedling rootstock and not the origi- 
nal scion variety. 
Most of our varieties are propagated from cuttings and 
hence are on their own roots. We will be glad to answer inquir- 
ies as to whether we can furnish particular varieties on their own 
roots. 
HARDY VARIETIES FOR EASTERN CONDITIONS: Certain varieties 
in this list should be satisfactory in favorably located sites along 
the Atlantic Coast from Long Island south. In the southeast and 
part of the east, high Summer temperatures and lack of humidi- 
ty, rather than Winter cold, are the limiting factors. The follow- 
ing varieties are probably the hardiest in this list: Arthur J. 
Ivens, Cynthia, Fastuosum flore pleno, Gomer Waterer, Lady 
Clementine Mitford, Lord Roberts, Mrs. Chas. Thorold, Mrs. J. G. 
Millais, Mrs. R. S. Holford, Purple Splendor. | | 
