Adult trees of satsuma mandarin 'Okitsu wase' grown in the open with a leaf: fruit ratio of 15: 1 were drenched in July with an aqueous solution of IAA. Meanwhile, young trees of 'Nichinan ichigo' grown in a plastic-house were pruned in late July and drenched in September with an aqueous solution of IAA, BA or Paclobutrazol. The treated trees initiated more fibrous roots and flower buds than did the untreated control trees. In late fall, carbohydrate content was higher in the new shoots but lower in the fibrous roots in the soil-drenched trees compared to their respective control parts. Thus, the C-N ratio in the stem of the new shoot was larger and that of the fibrous roots lower in the treated trees relative to those of the control. Another trial to 'Nichinan ichigo' was a soil-drenching treatment with L-proline solution in September. It promoted shallow fibrous root growth and flower bud differentiation significantly. The physiological basis for the enhanced flower bud differentiation of satsuma mandarin by soil-drenching with phytohormones and amino-acids and its possible use are discussed.