PROBLEM TO BE SOLVED: To provide a water retention structure for planting, with which the burden of watering control of trees, flowering plants, etc., planted on retaining walls for protecting slopes at sides of roads, rivers, etc., and on vessels such as containers, pots, etc., in roads, parks and houses is eliminated, a maintenance- free control is facilitated without requiring a skilled technique, the application can be carried out afterward in existing facilities and a control cost can be reduced. SOLUTION: This water retention structure for plants planted on retaining wall blocks or vessels such as planting containers, pots, etc., secures the planting area of root stock of a planted tree and comprises a water-absorbing unit body 4 to be arranged adjacently to the planting area. The unit body 4 is obtained by inserting a core material 3 of a three-dimensional network body into a bag body composed of a water-permeable sheet 1 and is constituted of a structure in which water-absorbing polymer particles are dispersed and arranged in void parts of the inserted core material 3 of the three-dimensional network body in the whole area of the bag body.
