Ask Mr. Smarty Plants

There probably isn't a one-size-fits-all answer to your question since all biennials are not created equally. However, in general biennials begin growing one year - often in late summer or fall - and typically form a basal rosette. In late winter or spring of the following year, they flower. Bud initiation is typically dependent on accumulated hours of cold temperatures. When the plant has been exposed to enough hours of cold temperatures, the plant will initiate flower bud development. When the weather warms sufficiently, the plant will produce flowers, often on a tall flowering stalk.

Nurserymen have long taken advantage of some plants' response to cold temperature bud initiation to induce flowering out of season. Valentines Day tulips are a good example of this practice, though tulips are not technically biennials. In practice, greenhouse growers accomplish this feat by keeping vegetative-stage plants in in cold storage for a predetermined period of time and removing them to a growing area a specified number of days before they are to be marketed.

For your experiments, if biennial seeds were started early enough in the year to allow for sufficient time (along with other required conditions) to grow the necessary basal rosette, then the plants were placed in cold storage for long enough to accumulate the chilling hours necessary to induce bud initiation, then the plants were removed from cold storage and placed back in a growing area, it would be possible to complete a biennial's growth cycle in one year. Some trial and error might be required to determine the optimal mix of pre-chilling, chilling and post-chilling days and other conditions necessary for success.