The confusing terminology of long day, short day and day neutral

-A A +A
By Broccoli Billy

With about 40 years of gardening experience I should have most things figured out in the gardens. I even have some working knowledge of ornamentals though they don’t taste good and many are poisonous. I now grow mostly vegetables here in Cedar Key and after all this time still have areas of confusion.

Let us take the terms long day, short day, day neutral and photo period. These terms are easily explained with no confusion! A long day starts at 7 a.m. and ends about 6 p.m., a short day starts at 8 a.m. and ends at 12:00 noon, day neutral is a day I had where nothing happened! The photo period is the time it took me to go and have my picture taken. These definitions are a world away from plants and our vegetable gardens.

The life cycles of most all plants is in tune with light in various amounts. Individual plants require certain amounts of light to attain their bloom cycle; this is called their individual photo period. We consume strawberries, tomatoes, squash, peppers etcetera, all of which are derived from plant blossoms. I do suppose that even a blooming onion could be had at the Outback, although we do not consume onion blossoms.

Our glorified seed catalogues, when referring to onions and strawberries, kindly tell us what varieties to plant in the north and south of our great nation. They even have varieties which will do well both places (day neutral). Long day varieties are planted in the north which has shorter day length than the south. Short day varieties are to be planted in the south which has a longer day length than the north. Now this is really starting to make sense!

Two common long day plants are dill - critical day length 11 hours - and spinach with critical day length of 13 hours. These plants must have these amounts of day light to initiate flowers. Two common short day plants are chrysanthemum and poinsettia with 15 hours and 10 hours respectively. Day lengths must be shorter than their critical day length to initiate flowers. Generally, day neutral plants have to reach maturity in order to initiate flowers and do not respond to day length at all.

Now remember that the terms long day and short day don’t refer to the length of critical day light. The key to this concept is whether the plant will begin flowering when the days are longer or shorter than their individual critical day lengths.

Finally, I have explained all the confusion about long days and short days. Oh! I almost forgot that eventually scientists discovered that the actual hours of “uninterrupted darkness” triggered flowering instead of the hours of light. Experiments show that even brief periods of light during the dark period of the cycle could interfere with flower development. Despite this new understanding we still use the old terms. If I could describe this column to my readers it would be day neutral.

Cumin you chard

Broccoli Billy