To provide a mooring means allowing the easy setting of a float island implanted with a plant and floated on a pond, especially a pond set in a roof, capable of controlling soil moisture according to the plant, and not affected by a wind or the like.

This float island comprises a buoyancy structure wherein buoyancy bodies 1 are combined in a frame state, and a planting container 2 having a bottom face with a mesh or porous structure stored and fixed in the frame. A watering water guide body 3 of a water-permeable nonwoven fabric is extended to the water surface from the container bottom face, a water- permeable nonwoven fabric 4 is laid on the watering water guide body 3 in the container bottom face, and soil 5 is filled thereon to form the float island. A columnar body 82 is erected on a base body 8 composed of a molded container filled with concrete, sand or the like, and a nearly central part of the float island is provided with a guide 83 vertically freely movably inserted through the columnar body 82 for the mooring. The columnar body 82 is surrounded by a vegetation support body such as a vine, or can be provided with a display and/or showpiece such that a parasol.