Abstract. Understanding root growth dynamics in cranberry vines can help growers adjust and target production practices (e.g., irrigation, fertilization, agrochemical applications, disease control, etc.) to period of active root growth, thus increasing production efficiency and reducing environmental impacts. The main objective of this study was to characterize cranberry root growth dynamics and root morphological traits, and develop a root phenology model to increase production efficiency and sustainability. A total of sixteen minirhizotron root observation tubes were constructed and installed in an angled position (30°) in the root zones of selected beds of ‘Stevens’ and ‘GH1’ at a farm in the Tomah, Wisconsin area during the fall of 2014. Root images were recorded from April 2015 to January 2016, and from April 2016 to November 2016. Root image analysis was performed using WinRhizo Tron analysis software (Regent Instruments, Quebec, Canada) and JMP statistical analysis software. During 2015 and 2016, new root production began during bloom time, and continued until after harvest. The highest rate of root production happened during and after harvest, which corresponds to the cessation of vegetative growth on the above ground portion of the plants. Root activity and production extends past harvest into mid-late fall, which might suggest that more attention should be paid to soil moisture levels during fall given that roots are still up taking water and nutrients. Over 90% of new roots observed were located in the first 4 inches (10 cm) of soil, which could be related to irrigation management in the marsh where the study was located. Note: The presentation is not available to download.