How to Use Our Minimum Photoperiod Recommendations (MPR) to Optimize Solanaceous Crop Production
the recommended MPR can result in delayed or reduced flowering or in some cases no flowering until the minimum is met. Use this information to select varieties that have a MPR that is the same or shorter than your natural day length to optimize flower power and finish time. For example, if the crop will be finished under natural day lengths of 12 hours, then select varieties with an MPR of 12 hours or less. If a variety you wish to grow has an MPR greater than the natural day length, then provide day-extension lighting. Day-extension lighting is defined as delivering a minimum 14-hr day length or 4-hour night interruption lighting (10 PM to 2 AM) with at least 2 µmols·m -2 ·s -1 of light. Lights can be as simple as a timer- controlled string of incandescent bulbs or LED holiday lights to professional greenhouse lighting systems.
The Natural Photoperiod by Latitude graph shows how the natural day length changes throughout the year depending on latitude. The photoperiod, or duration of light, that a crop receives can have a significant effect on flowering if the species is photoperiodic. Flowering of many spring annuals is influenced by photoperiod, for example, calibrachoa, petunia, Tagetes and Antirrhinum . In the finish production section of the Grower Success Guide, we list the Minimum Photoperiod Recommendation (MPR) for each variety of calibrachoa and petunia. The MPR is the minimum duration of light needed to produce these Solanaceous crops with marketable flower power and optimal finish time and is based on extensive trialing data. Not providing a photoperiod that is equal to or longer than
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