Debarking has potential to make short rotation woody crops economically competitive by both improving the quality of woody material and adding an additional product stream from separated bark. The ultimate strength of wood-bark interface was studied in this research relative to the development and optimization of debarking systems and strategies. Four genetically different varieties of shrub willow, three harvest times and different moisture levels were tested using universal testing machine, Instron®. The loading rate during tests was 0.5 mm min^-1 to maintain quasit-static conditions. Regression models showed that moisture content has a negative correlation with wood-bark bond strength, like observations made on other species. The harvesting time of year also affects wood-bark strength of shrub willow significantly (p < 0.01). Shrub willow harvested during the winter has significantly higher wood-bark bond strength compared to spring or summer. This may be due to seasonal changes in cambium layer morphology. Moreover, wood-bark bond strength is significantly different for genetically different varieties of shrub willow. Cultivar “Millbrook” has higher wood-bark bond strength than “Fabius”. It is likely that cross-linkages of calcium ions, and arabinan and galactan side chains of pectins are more common in varieties that have high wood-bark bond strength.