E.J. Fortanier
A period of approximately 6 years is required to obtain flowering of tulip bulbs from seed. Flower formation is controlled endonomously and depends on a minimal bulb weight. The annual increase in weight is small, mainly owing to the short annual period of active growth.

The minimal bulb weight required for flowering can be reached earlier when special temperatures are applied to shorten the periods of initiation, development and innate dormancy and to omit those of imposed rest. These treatments reduce the cycle length from harvest to harvest and make the increase of bulb weight per year greater. Cycles of 8 months appear to give the greatest shortening of the vegetative period and the earliest flowering of the largest number of seedlings. This system requires artificial growth conditions. If all stages are shortened to their minimal length, the cycle is reduced to 6 months. This allows an alternation of growth periods under natural conditions of spring in The Netherland with the same in a favourable climates in the Southern hemisphere. But trials indicate that the vegetative period will be shortened less, with a greater loss of seedlings and consequent a preselection on earliness, than with cycles of 8 months.

Fortanier, E.J. (1971). SHORTENING THE PERIOD FROM SEED TO A FLOWERING BULB IN TULIP*. Acta Hortic. 23, 413-420
DOI: 10.17660/ActaHortic.1971.23.68

Acta Horticulturae