Long-Day Plants (Short Night)
Plants form their flowers when the day length is less than about 12 hours in duration
Short-Day plants include many spring and fall flowering plants such as chrysanthemum and poinsettia

Day-Neutral
Plants form flowers regardless of day length

No Category
Some plants do not really fit into any category but may be responsive to combinations of day lengths
The petunia flowers regardless of day length but flowers earlier and more profusely under long days

Take-Home Message
You can shift plants from the vegetative stage into flowering [budding] by manipulating
day length between light and the uninterrupted dark period
It is critical not to introduce any light during the uninterrupted dark period as this may
confuse the plant and cause a premature shift to the flowering phase