Photoperiodism

Photoperiodism is the process by which plants react to the length of lighting they receive. This process may affect certain plants' growth and flowering.

Most indoor plants do well with 14 to 16 hours of lighting daily. Just as plants tend to fade if they do not receive sufficient light intensity, their growth and the formation of new leaves may suffer if the photoperiod is too short. On the other hand, a photoperiod longer than 18 hours will tend to produce pale green foliage and stunted stems.

Flowering in some plants is triggered by the daily length of lighting.

For instance, chrysanthemums, poinsettias and Christmas cacti all need short days in order to flower. They must be given a daily cycle of long, uninterrupted 14-hour nights for several weeks if they are to bloom profusely.

Some plants, such as calceolarias and tuberous begonias, will flower only if given long days and short nights.

Others, such as cyclamens, gloxinias, African violets and roses, do not require any particular cycle to bloom.

If you find controlling the photoperiod manually each day with artificial lights too complicated, an automatic timer will make it much simpler.