1. Coil for horticulture, particularly for supporting a suspension cable intended to hold a plant, comprising a hanger bracket and a coupled spinning reel through a shaft in the hanger bracket and defining the spinning reel surface between two strips in which is wound / unwound cable suspension fixed rotatably on the hanger bracket including the rotating spool a brake mechanism for blocking rotation of the rotatable reel, characterized in that the brake mechanism has a locking piece made of an elastic plastic material with shape memory, which is linked to means operable manually push by a user and an integral retaining means with the spinning reel, such that in a rest position the locking piece in frictional contact with the retaining means so that the spool is prevented from being rotated while in a position of free rotation of reel locking piece is elastically deformed with respect to the geometry adopts the locking piece in the rest position. 2. Coil horticultural according to claim 1, characterized in that the locking part comprises a ring with a substantially annular shape having at least an elastically deformable portion and at least one protrusion associated with a groove present in the retaining means , wherein the ring diameter adaptable to the geometry of the retainer means. 3. Coil horticultural according to claim 2, characterized in that the elastic ring has two deformable sections arranged diametrically opposite one another and between which the protuberance is located. 4. Coil for horticulture according to claims 1 and 2, characterized in that the retainer means comprises a circumferential flange projecting outwardly from one of the plates of the spinning reel, said flange at least the slot into which is insertable the boss. 5. Coil horticultural according to claim 1, characterized in that the biasing means is coupled to the thread locking part. 6. Coil for horticulture according to claim 2, characterized in that the locking piece includes an extension
