PROMOTION OF FLOWERING IN FREESIA PLANTS VAR. PRINCESS MARIJKE
Due to the relatively high light intensities and the moderate temperatures prevailing in most parts of Israel during the winter, we are able to grow Freesias throughout the winter in unheated plastic houses or under other types of light protection, such as saran-shade houses. A treatment that will advance the blooming date by one to three months will be of great value to growers, since it will extend the flowering season and shift part of the production to a season of better prices and higher demand.
The physiological requirements for flower formation and the regulation of flowering have been studied in recent years both in corms (3,4) and in seed-raised Freesias (5). It was found, that although photoperiod has some effect on flowering (6), temperature rather than day-length is the decisive factor which governs over growth and flowering in Freesia plants. The optimal range of temperature required for induction and formation of flowers is 12–15°C. Inductive temperature should be applied at the correct stage of development. The preparation of plants for cold treatment depends on the way they are raised, namely from corms or from seeds. It was found (5) that in order to obtain high-quality flower production in seed-grown plants, cold treatment should start when plants are at the stage of 6–8 leaves.
In corm-raised plants dormancy of corms should be broken before the application of cold treatment. The breaking of dormancy in Freesia, unlike in many tuberous plants like Gladiolus, is performed not at low temperatures but around 30°C. Flower formation in corm-raised Freesias, like in Gladiolus, starts soon after sprouting. Cold temperature is essential not only for flower induction, but also for its formation.
Hartsema (3,4) suggested the following treatment as a means for obtaining early flowering. It is based on her experiments with Freesia corms and comprises of storage for 10 weeks at 31°C and for 4 weeks at 13°C followed by planting in a cool greenhouse. However, Hartsema (4) states that "Practical growers did not succeed in using our method for production of early flowering, probably because the temperature in the greenhouse cannot be kept optimal at 13–15°C during September without refrigeration".
We tried the treatment recommended by Hartsema in a preliminary experiment. It was found, that under the conditions prevailing in Israel,