Fruit set and fruit retention are the most important events in sweet cherry production. For most cultivars this is the key to success. Only a few tools are available to improve fruit set and fruit retention. This study describes a new strategy in improving fruit set and fruit retention in cherries. Over three consecutive years (2014-2016) the application of the Ecklonia maxima seaweed extract, Kelpak®, was evaluated in trials on 'Bing' cherry trees by applying it either in the autumn (postharvest, previous season) or in the spring (flowering to pit hardening). Compared to the control, three autumn applications at 90, 100 and 110 days after harvest (DAH) and five spring applications resulted in a significant increase in fruit set in 2014. In 2015 a significant increase in the number of fruit plant-1 and kg plant-1 for a postharvest treatment at 110 and 120 DAH were recorded. Although no harvest data were available for 2016 due to severe frost damage, the starch levels in the flowers were measured at full bloom. The postharvest applications, 110 and 120 DAH, significantly increased the starch content in the flowers. A similar result was found for the three spring applications. The high starch content in the flowers may explain why fruit set was higher for these treatments in the previous years. Based on the yield performance in 2015, the best result, which was statistically different from the control, was obtained with the two 0.3% Kelpak sprays at 110 and 120 DAH.