SHORT DAY – LONG DAY – DAY NEUTRAL
Originally it was believed that the amount of daylight affected certain plant’s ability to flower.
Science has proven that it is actually the hours of darkness that trigger flowering.
Despite this, the terms long- and short-day, referring to hours of light, are still used.
Short-day
A plant that requires a long period of darkness to bloom. Plants form flowers only when day length is less than about 12 hours.
Long-day
Plants that require a short night to flower. These bloom only when they receive more than 12 hours of light.
Day Neutral
Some plants form flowers regardless of day length, flower once they’ve reached a certain age.
Do you want your edible plant to flower?
YES to broccoli, cucumber, tomatillo, melons, cauliflower, tomatoes, pumpkins, eggplant, peppers, beans, peas.
These terms are used for other things...
These terms are often used for plants that are SUITABLE for certain times of the year. Not just when they flower.
Example: Onions. Most onions are long-day however, here in Central/South Florida, if we grow these in the summer, they will never bulb and usually rot in the ground. Grow short-day onions during our winters and they bulb.
http://assoc.garden.org/courseweb/course1/week4/page15.htm
http://ext100.wsu.edu/skagit/wp-content/uploads/sites/5/2014/04/042712.pdf
http://www.johnnyseeds.com/t-library-vegetables-day-length-production.aspx