|Authors: ||A.A. De Hertogh, L. Gallitano|
|Keywords: ||Amaryllis, Hippeastrum, flower bulbs, flowering, geophyte, photoperiod, temperature|
Commercial forcing guides for Amaryllis (Hippeastrum) indicate that greenhouse temperatures should be 20–28°C (Barnhoorn, 1996; De Hertogh, 1996; Traub, 1958; Vijverberg, 1981) and that temperatures must not exceed 30°C or be lower than 20°C. A database to support these guidelines have not been found.
Therefore, a study was conducted in the NCSU phytotron in 1997 using Israeli-grown 'Apple Blossom' bulbs (26/30 cm, in circumference). One bulb was planted per 15 cm diameter standard depth plastic pot (1.8L) with one-third of the bulb above the surface of the medium, which was Sunshine Mix No. 4 (a mixture of coarse peat and perlite). Ten plants were subsequently placed at 18/14, 22/18, 26/22, or 30/26°C (Day/Night) and under either a short day (9 hr. photoperiod) or a long day (3 hr. night break with incandescent lights). Ten plants were also forced under standard greenhouse conditions and they served as a control.
Data was recorded at marketing and first flower stages of development.
Satisfactory plants were produced at 18/14°C, 22/18°C, and 26/22°C under long and short day conditions.
The highest quality plants were produced at 22/18°C with long days.
These plants reached the market stage in 25 days and had 15.4 cm leaves.
They reached full flower in 32 days with 18.6 cm leaves, 43.6 cm tall flower stalks, and 19.3 cm diameter flowers.
The lowest quality plants were obtained at 30/26°C under both short and long day photoperiods and greenhouse conditions.
Plants grown at 30/26°C were very short and had small diameter flowers.
They also produced very light pink flowers indicating the pigmentation process was markedly affected.
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