Answer:
short dark periods
Step-by-step explanation:
Based on the information provided within the question it can be said that the Clover will flower with short dark periods. This is completely following the instructions that have been provided since short dark periods allows the Clover to receive enough sunlight in order for it to flower. As mentioned even long dark periods may be acceptable if they are interrupted by brief periods of light which causes the dark periods to become various short dark periods.