American Rose Annual, 55:74-77 (1970)
Blind Wood Its Causes
Dr. Merlin L. Cooper
Each year the development of blind laterals on some varieties of Hybrid Teas in my rose garden, stimulates a continued interest in the CAUSE, and I continue to wonder why some plants produce an occasional or few or many or even 100 percent blind laterals devoid of blooms, I have asked numerous rosarian friends, "What is the cause?", and invariably the answer is "The cause is not known". Such an answer is not only not satisfying, but it is sufficiently irritating to stimulate continued observation and study of this phenomenon.
During the past 20 years I have observed every bush of the different varieties of Hybrid Teas in my garden for the development of blind laterals, and have made the following observations:
1. Blind laterals are produced in larger numbers and upon more varieties during the early spring burst of growth.
2. Short blind laterals frequently originate from surface eyes on old wood quite low on the plant.
3. Careful inspection of longer blind laterals may reveal that they originated from old canes showing surface evidence of past winter damage and/or interior abnormality revealed by dark brown discoloration of the pith which may extend laterally to that portion of the surface of the old cane showing brownish discoloration.
4. Some varieties, such as 'Rubaiyat', have never developed blind canes in my garden.
5. Some varieties, such as 'Chrysler Imperial', are disposed to develop a few or numerous or even 100 percent of blind canes. The latter condition was observed on a potted specimen which, after planting, grew to a height of 20 inches, produced excellent foliage but completely blind.
6. Some varieties, such as 'Crimson Glory', are disposed to develop few blind laterals low on the plants.
These observations stimulate the following questions:
1. Is an inherent or genetic cause of blind wood indicated by the apparent insusceptibility of 'Rubaiyat', the marked susceptibility of 'Chrysler Imperial' or the moderate susceptibility of 'Crimson Glory' and even lesser susceptibility of other varieties?
2. Is cane abnormality or subnormality indicative of the cause of blind wood as seen on new canes originating from subnormal old canes?
3. Is a plant subnormality indicative of the cause as demonstrated by a plant of 'Peace' which did poorly in a rose bed in the front yard, was transferred to my 'hospital" bed, continued to do poorly and this year has three pencil-size canes with all laterals completely blind?
4. May apparently normal canes, which give rise to blind growth, in fact subnormal nutritionally? This probability would seem to be ruled out in a garden containing many rose plants growing and blooming exceptionally well under similar conditions of fertilizing, spraying, watering, winter protection and quite severe spring pruning. However, it is common experience among rosarians to see a rose plant perform beautifully after being transplanted to a different location in the rose garden, in contrast to a poor performance elsewhere in the same garden. Being dissatisfied with my own observations, I wrote letters this spring to eleven outstanding rosarians asking for their opinions regarding the cause or causes of blind wood and I would like to share with you their pertinent comments which follow as quotations:
1. All respondents emphasized "The cause is not known?"
2. "With greenhouse roses such as 'Forever Yours', one of the worst in the matter of producing blind canes, the best preventive is to keep the calcium content of the soil about 200 parts per million and the potash content at 20-30 on the Spurway scale".
3. "'Mister Lincoln' will produce many blind stems if the nitrogen content of the soil is too high and the calcium too low".
4. "Severe defoliation will often temporarily increase the percentage of blind wood and it is possible that some hormonal mechanism is responsible for blindness rather than its cause being the direct result of such environmental factors as light intensity, temperature and nutrition".
5. "In a panel discussion on this subject the consensus was that certain varieties, such as 'Chrysler Imperial', were more apt to develop blind wood than others".
6. "Two test plants of 'Pascali' produced numerous canes but none developed blooms as first grown. However, when the blind canes were shortened all produced good blooms later, so I think blind wood at first does not mean much".
7. "Four years ago I experimented on blind shoots in two of eighteen rose beds where blind shoots were always present. The rose plants in the two beds were fed 50 percent more than in previous years and 50 percent more than in the other 16 beds. I am not certain that this extra feeding in large quantities on these two beds was the reason, but there were hardly any blind shoots in the two beds all season".
8. "Most of my varieties, especially those in pots, were likely to have blind wood in the spring, but when recognized and cut back, blossoms soon appeared".
9. "Studies attempting to induce blind wood by varying the nutrient levels, light intensities and photoperiod were never conclusive. My own observations lead to the conclusion that the problem is basically one of heredity. Some varieties are much more prone to the production of blind wood than others. Possibly some special environmental factors may affect the expression of the hereditary factors for blindness. None of the many conjectures as to the cause of blindness are backed up by any convincing experimental evidence. While it would seem that conditions for optimum growth would result in fewer on no blind shoots, I am not sure this is the cause".
10. "As a botanical fact, all newly sprouted rose canes should terminate in bloom; at least the apical or terminal bud should be a bloom. Blind buds are ordinarily confined only to the apical bud and usually if this is cut off, blooming will proceed normally. Too much fertilizer, particularly with nitrogen, will stimulate too much vegetative growth at the expense of blooms".
Conclusions regarding the cause of blind wood:
1. Perhaps inherent or hereditary factors are the underlying cause.
2. Perhaps subnormal nutritional or environmental conditions are contributing factors.
3. Perhaps subnormal or winter damaged canes, from which blind canes originate, are the immediate cause in such instances.
4. A single proven and accepted cause is still unknown.