The aqueous extract of Salix spp contains many compounds which may act as root-promoting agents in cuttings. S. alba is a deciduous tree containing variable phytochemicals which are variable throughout the year. So, in this study, one- and two-year-old shoots of S. alba were collected on the 15th of each month in the year 2022, extracted in 2% ethanol at 9 g.L-1, and placed in a water bath at 35 {\deg}C, then they applied to thornless blackberry cuttings for 1.5 hr. The results explained that the highest rooting percentage (66.67%) was obtained in the cuttings soaked in the extract of willow shoots collected on 15th of January. They were not significantly different from control cuttings, but they were different from the cuttings soaked in the extract of willow shoots collected on 15th of August and October (33.33%). The majority of other shoot and root traits were high in the cuttings soaked in the extract of willow shoots collected on 15th of December. The willow shoots collected on 15th of January contained the lowest total phenols (51.4 {\mu}g.mL-1) and total flavonoids (29.07 {\mu}g.mL-1). Moreover, the highest total phenols (57 {\mu}g.mL-1) and IAA (365.17 {\mu}g.mL-1) were recorded in the willow shoots collected on 15th of March, however each total flavonoids (44.96 {\mu}g.mL-1) and salicylic acid (492.61 {\mu}g.mL-1) were the highest in the willow shoots collected on 15th of April. Generally, based on rooting percentage, it is advisable to collect willow shoots on 15th of January and February for extraction and application to the thornless blackberry cuttings.