INFLUENCE OF VARIOUS COLD TREATMENTS ON THE REACTION TO FORCING OF MINIATURE HYDRANGEA MACROPHYLLA

• research for a minimum duration of cold treatment compatible with a good quality of plants and a suitable forcing duration ;

• behaviour of various miniature cultivars.

In 1983/1984, we studied five cultivars (‘Bodensee Blue’, ‘Rosita’, ‘Sybilla’, ‘Leuchtfeuer’, ‘Alpenglühen’) and also the traditional cultivar ‘Merveille’ in order to confirm previous results.

The plants were placed into cold storage rooms with their leaves.
Three durations of cold treatment (+ 2° C) were applied : 3, 4 and 5 weeks.

The forcing in greenhouse (+ 18°C) started on Dec. 1st.

In our conditions of experimentation, the results show that the optimum duration of cold treatment is four weeks for ‘Sybilla’, ‘Leuchtfeuer’,

‘Alpenglühen’or five weeks for ‘Bodensee’ and ‘Rosita’, provided the aim is the best possible earliness of flowering.
On the other hand, the four-week duration of the treatment makes it possible to get smaller plants whose quality is good (diameters of flowers).

The results obtained with ‘Merveille’ confirmed the tests of the previous years : a three-week duration gives the best results.

The 1984/1985 experiment should enable us to complete these conclusions for ‘Bodensee Blue’, ‘Bodensee Pink’, ‘Rosita’, ‘Sybilla’, ‘Leuchtfeuer’ and ‘Immaculata’, under three and four-week cold treatment with their leaves.