American Rose Annual, 40-42 (1920)
Night-Growth of Roses
By A. W. GREELEY, Williamsport, Pa.

EDITOR'S NOTE.—Last year's Annual included an article on "Winter Work with Roses" by a busy newspaper editor, which attracted much attention. This year the same busy editor gives us another fascinating story, based on his own novel point of view, and adding interest to the work of the rose amateur who earn to develop the idea. It is these "different" things which may be done with roses, more especially by the thoughtful amateur, that give rose-growing such a high rank as a recreation.

AN interrupted, and therefore incomplete, study of certain phases of rose-growth, made during the past summer, points tentatively to the conclusion that from 60 to 80 per cent of rose-cane growth is made during the night. The study was begun with the object of finding the reason for the more favorable results obtained by watering rose-beds in the morning, compared with the relatively unsatisfactory results alleged to follow evening and night watering of roses. As planned, the study involved, among other things, the systematic recording of soil and atmospheric temperatures in two similar beds of roses, one watered in the morning and the other at night and the effect of varying application of fertilizers, sprays, etc., but events made it impossible to carry out the plan in full. However, certain measurements of rose-cane and bud growth, incidental to the general plan of study, but more or less complete in themselves, are rather suggestive, and may prove of some little interest to rosarians in general. These measurements also point to a possible explanation of the fact that better results follow the practice of morning watering of roses.

Measurements of cane-growth and bud development were made of a number of varieties of Hybrid Teas from the middle of June to the first few days in July, including in the list a Lady Pirrie, a Radiance, and a Killarney Queen. The growth-chart of a cane of the Lady Pirrie is typical, and the tendencies shown therein are also reflected in varying degrees in the growth-charts of the other varieties. All the plants under observation were vigorous, four-year-old, selected, Multiflora-budded stock, the beds were standard (Thomas), and the cultivation normal. A few days before measurements were made, liquid manure was applied and the beds worked to a depth of three to four inches. The measurements were begun with the first appearance of a tiny bud on the growing cane.

The outstanding and important fact to be deduced from the Lady Pirrie chart (see below) is that a fraction more than 63 per cent of the cane-growth was made at night, between the recording hours of 7 P.M. and 7 A.M., leaving a fraction more than 36 per cent for the total day-growth from June 19 to July 4. The total growth of the cane from the appearance of the bud until the perfected bud was ready for cutting, was 12 3/4 inches, of which 8 1/2 inches was night-growth, and 4 5/8 inches was growth registered in the daytime. The greatest single night-growth, 1 1/4 inches, occurred June 10, following two cloudy days, with rainfall of 0.71 inch, and following a mean temperature on June 19 of 78.5° and a mean night temperature of 73°. The greatest single day-growth, 3/4 inch, was also registered at this time, June 20 and June 21.

The Radiance chart of growth, for the same period as that of the Lady Pirrie, puts even greater emphasis on night-growth, 80 per cent of its growth in this time being made at night. In nine days out of fourteen, it made no appreciable growth in the daytime. The Killarney Queen, on the other hand, made only 54 per cent of its total growth in the night-time. Nevertheless, every rose under observation made more growth during the night than during the day.

Incomplete as are the observations, yet the fact is apparent that the rose does not sleep at night. It knows no eight-hour law, and the hours of darkness are the moments of its greatest building activity. Is it not reasonable, then, to suppose that a drenching at this time with cold hydrant water, by lowering the soil and plant temperature, would have a retarding influence upon plant-growth? And would not retarded growth mean, other things being equal, lowered vitality, resulting in inferior growth and reduced power of resistance to disease?

The Lady Pirrie chart is interesting from another point of view. In the 1919 Annual certain charts were published which tended to show that the optimum condition of rose-bloom occurs when the temperature ranges between 60 to 85. The Lady Pirrie chart tends to confirm this deduction by showing that the optimum condition for rose-cane growth is likewise dependent upon this range of temperature. Whenever, as on June 22 and 28, July 28, 29 and 30, the mercury drops below 60, the growth-curve flattens out into a "no-growth" or into a retarded growth section. Likewise, when the temperature rises above 85 we find a similar flattening of the curve indicative of retardation and stoppage of growth. Furthermore, the temperature relation appears to be so dominant that its influence persists regardless of the influence of other factors such as sunshine, cloudy days, and rainfall.

The chart suggests a number of other interesting leads for speculation, but the data at present is so incomplete that it would not be wise to draw hard and fast deductions. In fact, the entire subject of this brief article is presented with some diffidence and self-distrust, and its suggestive value to other rosarians is very likely its main merit, if there be any such quality concealed within its sentences.

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