If the critical photoperiod for a short-day plant is 13 hrs of daylight, will it flower when there are 15 hrs of daylight?
A short-day plant requires a minimum level of darkness in order to flower. It follows then that under natural conditions, the plant may also be said to have maximum level of daylight, beyond which it will not flower, since there will not be adequate hours of darkness remaining in the 24-hour period. In this example, the critical level of daylight is 13 hrs, and any level of daylight beyond this will not allow the plant adequate hours of darkness. The plant will, therefore not flower when there are 15 hrs of daylight.