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Photoperiodism

Did you know that plants use a special plant chemical to measure how long they're exposed to light and darkness each day? The length of light and darkness exposure changes as the seasons change and effects many different aspects of plant life cycles, including the production of flowers, fruit and other edible produce.

Some plants have specific night length requirements so planting times become very important if you want them to be productive. Originally, it was thought that the day length was the important factor so plants are still categorised as short or long day plants or day neutral plants. Check back tomorrow for some examples of each.

Short day plants

Short day plants begin to produce bulbs or flowers when days are short. Garlic and onions for instance, need short days and long nights to start producing large bulbs. That is why they should be planted in autumn or early winter - they will be exposed to short days that will trigger bulb formation and then the bulbs will grow larger as days become longer. Chrysanthemums and many strawberry varieties need long nights to begin flower production. Cotton and sugarcane prefer long nights and short days but will eventually flower if they don't receive them.

Long day plants

Long day plants on the other hand, only begin to produce flowers and bulbs when days are long and nights short. Dahlias, carnations, oats, some clovers and some sweet peas for instance, only produce flowers during late spring and summer when the days are long so should be planted in spring. Lettuce and turnips are examples of plants prefer long days and short nights.

Day Neutral plants

Some plants will produce flowers at any time (temperature and water etc. permitting) and don't mind whether they days are short or long. You can for instance, buy day neutral strawberries that will flower and fruit whenever the temperature is right, regardless of how long the days are. Roses, tomatoes and corn are other examples of day neutral plants.

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