It consists of a plastic sheath (1) in which uprights (2) prestressed at (4) and held by a head (3) are introduced. The action of the stressing (4) on the uprights (2) imparts a geometrical shape by means of reaction of the sheath (1). One or more inserts (5) are clipped onto the uprights (2). Of a twisted groove support (8), of a positioning adaptor (10) along the support (8), of a shoe block (14) and of a stirrup piece (16) forming an adaptor for fastening on the tubular frame (17) provided with connectors (23) and irrigation nozzles (19). The frame (17) is fixed in rotation by plain bearings (22) on arms (21) rendered retractable by lifting with racks (24). The device according to the invention is particularly intended for covering surfaces planted with market-garden and ornamental plants. <IMAGE>
