A Rose Odyssey (1937)
J H Nicolas

Arcticness and Mathematics

ON EACH of my trips abroad I have concentrated on one particular subject. In 1932 winter hardiness was my chosen query.

In catalogues and rose descriptions "hardiness" is the most misused word of the English language. A Southerner will call Maréchal Niel "hardy" because he finds it so in his climate. At best, hardiness is relative, varying with the location of the grower using the word. This word, applied to a rose, originally meant its ability to withstand severe winter conditions, and in Germany they emphasize that meaning by saying "winter hardy."

This chapter is the résumé of many conferences with hybridizers and growers. It was in one of those conversations that the word "arcticness" came into rose parlance. Hardy is relative. A rose is not necessarily hardy in Labrador because it is so in the Fiji Islands, yet a catalogue from Fiji circulating in Labrador would infer that. Arctic is positive, with the more precise meaning of ability to withstand arctic conditions wherever they may be.

The English growers gave me much help in computing the following table, and at their request it was first published in the National Rose Society Annual of 1934. It created much interest in the European rose circles.

Arcticness, meaning ability of a plant to withstand arctic temperatures and conditions, depends upon both inborn and external factors.

Inborn arcticness is in the race. Each straight major strain has an average arcticness in its original habitat which varies perhaps to the extent of 10 per cent plus or minus, according to local conditions, when transplanted elsewhere.

Some plant breeders claim that the arcticness of a hybrid can be determined by the mathematical ratio of natural arcticness of the two parents. However, it is doubtful whether nature always works by mathematics. If it did, hybridizing would be an "exact" science and lose its greatest charm, the Unknown! The average arcticness of the progeny of a cross may be estimated by mathematics, but that estimate will have to be confirmed for each individual seedling by test because of the uncertainty of heredity. A Rugosa crossed with a Tea may give a progeny of a varied intensity of arcticness. In some of the progeny the Rugosa arcticness may be dominant, while in others it may be more or less recessive. At any rate, one may establish a tentative scale as a suggestion of possible arcticness of a hybrid as a help in selecting varieties for one's climatic conditions; it will also help hybridizers to select the proper parents so as to obtain the degree of arcticness desired in the progeny.

This might be compared with the life‑expectancy tables of insurance companies. A person of a given age may expect to live so many more years provided all goes well with him.

The following table may be used in computing the expectancy of arcticness of a variety when we know the true ancestry of that variety. This table covers the range from 32° F. (0 C.), freezing point, at which no arcticness is necessary, to ‑30° F. (‑36° C.), to survive which a plant must be 100 per cent arctic.

Those ratings do not mean that plants will resist all injury. It is possible that soft tips of late growth may freeze, but the main body of the plants will come out unscathed. The precautionary measure of hilling up the base of the plant should not be overlooked, especially where frost is likely to reach the maximum rated for the variety for any length of time.

Winter Temperature Necessary
32° F. 0 C. 0%
30° " -1 " 5%
25° " -4 " 10%
20° " -7 " 15%
15° " -10 " 20%
10° " -13 " 25%
" -15 " 30%
" -18 " 35%
- 5° " -21 " 45%
-10° " -24 " 60%
-15° " -27 " 75%
-20° " -30 " 90%
-30° " -36 " 100%

For rating we will assume the following percentages of arcticness:

100% Multiflora, Rugosa groups, most northern U. S. and Canadian species, most northern and western Chinese and Japanese species.
90% Centifolia (including Moss), Damascena and most Austrian briars. Species of northern continental Europe.
75% Wichuraiana, Canina groups, Gallica, Austrian Copper, Scotch Roses, Pompon Polyanthas.
60% Central Europe species, central Chinese species, most Hybrid Perpetuals.
45% Bourbon, some Hybrid Perpetuals, large-flowered Polyanthas.
35% Chinensis (Bengal), some early Pernetianas.
30% Some Hybrid Teas, most Pernetianas.
25% Most Hybrid Teas and Pernetiana Hybrids.
20% Some Garden Tea varieties (Hybrid Teas with Tea dominance).
15% Himalaya group (Sericea).
10% Moschata group, Cherokee, Bracteata, Banksiae.
5% Southern Chinese species.
0% Tea groups (including Gigantea).

As an illustration of how this table works let us consider the average Hybrid Perpetual. Theoretically a Hybrid Perpetual is a cross of Centifolia and Chinensis. This gives us the ratio of 90 plus 35, average 62.5, so we may expect a Hybrid Perpetual to withstand uninjured about 11° F. below zero. This Hybrid Perpetual (62.5) crossed with a Tea (0) gives us the Hybrid Tea with a ratio of 62.5 plus 0, average 31, indicating that the true Hybrid Tea should be able to stand 5° F. above zero or a little lower. But the Hybrid Tea class is so complex that there is certain to be a great variation of arcticness. For instance, the above Hybrid Tea (31) crossed again with a Tea remains a Hybrid Tea with Tea dominance, and its score goes down to 20, indicating a maximum arcticness of 150 F. If this Hybrid Tea (20) is again crossed with another Hybrid Tea of direct Hybrid Perpetual and Tea parentage (31) the progeny of the cross will score 25.5, indicating a capacity to withstand a temperature of 10° to 5° F.

The difference in arcticness between a rambler and a large‑blooming climber may be explained by their individual ratio: Dorothy Perkins (Wichuraiana 75, plus Hybrid Perpetual 60) scores 6.75 and stands about 12° or 13° F. below zero, while Dr. W. Van Fleet (Wichuraiana 75, plus Hybrid Tea 30, plus Hybrid Tea 30) scores 41.25 and is not able to stand much more than zero without protection. Silver Moon, which is supposed to be a hybrid of Wichuraiana, HT and Cherokee, scores about 37 and freezes badly at zero temperature.

Early Pernetianas (ignoring for a moment their debilitating proclivity to summer defoliation) are decidedly more arctic than the average run of Hybrid Teas. Let us study Souvenir de Claudius Pernet. Its original ancestors, Antoine Ducher, HP (60), and Persian Yellow (90), produced Soled d'Or (75), which is even more arctic than many Hybrid Perpetuals. The pollen of Soleil d'Or was probably applied onto a strong Hybrid Tea; ratio 75 plus 30, mean 52.50.

Some selfed seeds and interbreeding, then we know that Melanie Soupert, Hybrid Tea (30), was the seed parent of Lyon Rose, which means 41.25. From Lyon Rose to Claudius came a long series of selfed seeds and crossbreeding, perhaps an occasional Hybrid Tea but always pollenized with a "direct descendant of Soleil d'Or" (said Pernet), so it is most rational to give to Claudius a rating of 40 to 45 (0 to 5° below), which tallies perfectly with our long experience of Claudius as a garden rose in various sections.

External arcticness, as the word implies, refers to conditions foreign to the constitution of a variety in a normal state of health and vegetation.

Growers reported that some roses winter much better than others in their vicinity because they have been well fed and were full of vitality when forced into winter dormancy. This stands to reason. Hibernating animals fatten and grow a thick fur during the summer in preparation for their prolonged sleep. Should they go into winter in a lean condition and a thin fur they would never awaken in the spring. So it is with plants.

The optimum state of health and nutrition depends not only on soil fertility but also on the condition of the foliage throughout the season. Foliage is the "fattening" agent of the plant. A proper slogan might be "save the foliage and you save all."

Of course all this is highly theoretical and many probabilities (should nature actually work with exact mathematics) are defeated or altered by local conditions, such as atmosphere and wind, elevation, drainage, health status of the plants, maturity of the wood at transplanting time, etc.

Atmospheric conditions either aggravate or lessen the effect of cold as registered by the thermometer. Continuous cold winds from the same direction are more deadly than a much colder thermometer with a still atmosphere. A protracted cold spell, although not of the minimum temperature assigned to a variety, is more injurious than a short snap several degrees lower than the minimum. For instance, a variety rated at 10° F. will likely suffer less from a snap at 5° than it will from a long continuous siege at 15°.