Quality optimization of flax fibre through durational management of water retting technology under sub-tropical climate

•Durational tank-water retting of flax needs to be explored in sub-tropical climate.•Weight loss rate of flax-fibre was increased upto fourth day of retting.•Tank-water retting of 4–6 days is the best to get best quality of flax-fibre.•Less than 4 days retting resulted in under-retted stems and more than 6 days gave over retting.