NIGHT-INTERRUPTED LIGHTING OF NURSERY-GROWN HERBACEOUS PERENNIALS IN THE SOUTHEASTERN USA^©

Plant responses to day length were discovered and defined during the first half of the twentieth century.
Plants may be classified as short-day, long-day, or day neutral in their response for flowering.
Short-day plants are those that initiate flowers when the day length is shorter than their critical day length.
Day lengths longer than the critical day length result in vegetative growth.
Conversely, long-day plants are those that initiate flowers when the day length is longer than their critical day length.
Day lengths shorter than the critical day length result in vegetative growth.
The critical day length is the break-point day length above or below which plants perceives long or short days, respectively.
These two categories may be further classified as qualitative or quantitative.
In a qualitative photoperiodic response, the requirement for a specific photoperiod is absolute for floral initiation.
In a quantitative photoperiodic response, flowering is faster or plants have more flowers if provided the correct photoperiod, but plants eventually flower regardless of photoperiod.
In day neutral plants, floral initiation is not correlated with photoperiod.
Plants initiate flowers after reaching a specific size or stage of development.

Proceedings of the International Plant Propagators Society – 2012

J.R. Kessler, Jr., G.J. Keever

https://doi.org/10.17660/ActaHortic.2013.1014.85