2017 ASHS Annual Conference

Delivering the proper photoperiod is essential for many species of floriculture crops to induce or prevent flowering. For long-day crops such as Calibrachoa spp., knowing the critical photoperiod is important for finishing plants within a production schedule and with sufficient flowering and quality to attract consumers at retail. Experiments were performed at Syngenta Flowers, Gilroy, California with 23 varieties of the Callie® Calibrachoa series to determine the influence of photoperiod on finish time, flower number, and plant vigor. Plugs were propagated for 3 weeks and then transplanted into 15-cm pots and grown in controlled environment greenhouses with a 10- or 10.5-hr day that was extended with 150-W HPS lamps to achieve photoperiods of 10, 10.5, 11, 11.5, 12, 12.5, 13, and 13.5 hr. Average daily temperatures and daily light integrals were similar among the photoperiod treatments. Each experiment consisted of 10 replications (pots) per variety in each photoperiod and plants were grown until finish stage (5 open flowers per plant). Flowering data were analyzed to determine the minimum photoperiod required for flowering of each calibrachoa variety to avoid no more than 1 week delay in crop time and no more than 50% decrease in flower number compared to 13.5- or 14-hr photoperiod treatments. Over half of the varieties flowered under 10.5 or 11 hr and all of the varieties flowered under photoperiods ≥13 hr. Using the minimum photoperiod information, a customized grower tool was created that allows the selection of Callie Calibrachoa varieties that can be grown under natural photoperiods during the production period and which varieties require long-day photoperiodic lighting. Photoperiods change throughout the year and depend on location, specifically latitude. The tool is customized to the growers’ latitude to the nearest 5° and shows a graph of their natural photoperiods throughout the year for reference. A comparison of how each variety finishes relative to one another under five different photoperiods is also provided. This is a valuable tool that allows growers to choose the varieties that best match their location and production schedule to ensure high quality flowering calibrachoa ready for retail.