THE EFFECT OF DAYLENGTH AND TEMPERATURE ON FLOWERING IN THE AZALEA CULTIVARS 'RED WING' AND 'REINHOLD AMBROSIUS'

H. Pettersen, T. Kristoffersen
Studies on the effect of daylength on flowering in azalea have led to different conclusions. One might find azalea classified as a short day plant, as a day neutral plant and even as a long day plant. The reason might be that the cultivars react differently, or that proper attention has not been paid to the effect of temperature on the flowering process in this plant.

Skinner (1940) found that long days and high temperatures increased number of flower buds in the cultivars 'Hinodegiri' and 'Pink Pearl', while Kiplinger and Bresser (1951) found that short days had a favourable effect on flower bud formation in 'Coral Bells'. They suggest that the higher temperature caused by the black cloth may have an effect. Kiplinger (1952) found no effect of short day treatment on the time of flower bud initiation in this cultivar. McDowell and Larson (1966) dissected shoots of 'Alaska', 'Hershey Red', and 'Red Wing' grown in short or long days, but did not observe any effect of daylength on flower bud formation.

On the other hand, the results obtained by Stuart (1962, 1965) indicate that short days may retard shoot growth and further flower bud formation in several cultivars, as i.e. 'Coral Bells', 'Alaska' and 'Hexe'. Criley (1966) dissected shoot apexes of 'Hexe' and found that short days gave a more rapid flower bud formation. Bachthaler (1967) did also find that short days retarded shoot elongation and furthered the formation and the development of flower buds in 'Paul Schäme' and 'Ernst Thiers'. He also observed that night temperature of 15 or 20°C gave a more rapid bud formation than a night temperature of either 10, 25 or 30°C when the day temperature was the same and never below 20°C.

Many experiments have shown that low temperatures prior to forcing are required in order to obtained a rapid and uniform flowering of azalea. Post (1943) showed that 'Coral Bells' stored at 4–5°C after flower bud formation flowered uniformly after 4 weeks of forcing. Stuart (1965) who has carried out extensive storage experiments with azaleas, found that very low storage temperatures (1–2°C) delayed flower development during forcing and recommends storage temperatures closer to 10°C. Such temperatures do, however, cause leaf drop. This may be reduced by the application of artificial light.

Experiments carried out in order to study the effect of temperature and daylength on flower formation and the effect of storage temperatures

Pettersen, H. and Kristoffersen, T. (1969). THE EFFECT OF DAYLENGTH AND TEMPERATURE ON FLOWERING IN THE AZALEA CULTIVARS 'RED WING' AND 'REINHOLD AMBROSIUS'. Acta Hortic. 14, 27-38
DOI: 10.17660/ActaHortic.1969.14.3
https://doi.org/10.17660/ActaHortic.1969.14.3

Acta Horticulturae