SOME EFFECTS OF TEMPERATURE ON GROWTH AND FLOWERING IN THE CARNATION CULTIVAR 'WILLIAM SIM'

Many experiments have been conducted in order to study specific temperature effects on carnation grown in the greenhouse year around with changing daily light energy and daylength. Hanzel, Nelson, and Kiplinger (1955) state that the time required from pinching to initiation of flowers is temperature-independent.

Low temperature stimulates the initiation of flowers and increased temperature will normally result in more rapid development, more leaf pairs to be initiated prior to flower initiation, shorter internodes, weaker stems, reduced flower size, reduced cut flower life, and reduced branching. (Post 1942, 1949, Halliday and Watson 1953, Blake 1955, Blake and Spencer 1958, Hanan 1959, Kohl 1961, Harris and Harris 1962, Freeman and Langhans 1965a, Abou Dahab 1967).

Calyx splitting which is a well known problem in carnation production is caused by the formation of a large number of petals or by lateral buds inside the calyx at low temperatures (see Holley and Baker 1963 for references). Kohl (1961) demonstrated that the flower bud is most sensitive to low temperature when it is 3–6 mm in diameter. Temperature fluctuations at the time the buds open up, may also cause calyx splitting (Holley and Baker 1963). The results obtained by Freeman and Langhans (1965a) are however, not conclusive. In one experiment the largest percentage of split calyxes was obtained at low temperature and when high and low night temperature was applied. In an other experiment more calyx splitting occurred at high temperature, the day temperature having a minor effect.

The carnation is a facultative long day plant, and the effect of temperature on growth and development may be modified by the daylength (Laurie and Poesch 1932, Arthur and Harwill 1938, Post 1942, 1949, Blake 1955, Blake and Spencer 1958, Pokorny and Kamp 1960, Harris and Griffin 1961, Harris and Harris 1962, Freeman and Langhans 1965b, Harris and Ashford 1966, Harris and Bradbeer 1966, Abou Dahab 1967). The shoots are most sensitive to daylength when 5–7 leaf pairs are visible. In long days 8–10 leaf pairs and in short days 16–18 leaf pairs may be initiated prior to flower differentiation. The daylength has no effect on the rate of development from visible flower buds to anthesis, but more calyx split has been detected in long than in short days.

The growth and flowering in carnation is also positively correlated