Abstract: A plant-growing method for greening upright or slant wall surface is disclosed. A flexible bag is first prepared including a plurality of compartments sequentially juxtaposed in the direction of the overall length of the bag. The compartments are each provided with a plurality of openings communicating with the exterior. Soil is then loaded through the openings into the compartments with the bag being horizontally laid. Afterwards, trees are planted through the openings into the compartments. Thereupon, the bag which has been planted with the trees is suspended along the wall surface in the direction of the overall length of the bag while allowing trunks of the trees to be exposed through the openings. Water is thereafter supplied into the compartments of the bag to promote the growth of the trees.