A single-piece tray for hydroponic cultivation, composed of a plastic material shaped so as to define inside the tray a plurality of identical cultivation cells, each cultivation cell having: a housing defining a raised plane and configured to house a bulb or seedling to be cultivated, said housing having a hole with dimensions such as to support the bulb or seedling to be cultivated without letting it fall through, while allowing its roots to protrude below the tray; a buoyant portion defining a lowered plane intended to sink below a waterline when the tray is placed on the water, said portion being delimited by side walls which extend upwards from the lowered plane and are connected to said raised plane, each buoyant portion defining: - a first inner volume with a first height (h 1), designed to remain below the waterline as soon as the bulb or seedling to be cultivated is placed in the cultivation cell, - a second inner volume with a second height (h 2), configured to remain above the waterline when the bulb or seedling to be cultivated is placed in the cultivation cell and to sink below the waterline completely when the bulb or seedling to be cultivated has become a mature plant, - a third inner volume with a third height (h 3), configured to remain above the waterline when the bulb or seedling to be cultivated has become a mature plant; the sum of said first height (h 1), second height (h 2) and third height (h 3) corresponding to a height of the side walls between said raised plane and said lowered plane and wherein said side walls extend as far at least one free edge of the single-piece tray and define a channel which communicates with a space outside the single-piece tray. a housing defining a raised plane and configured to house a bulb or seedling to be cultivated, said housing having a hole with dimensions such as to support the bulb or seedling to be cultivated without letting it fall through, while allowing its roots to protrude below the tray; a buoyant portion defining a lowered plane intended to sink below a waterline when the tray is placed on the water, said portion being delimited by side walls which extend upwards from the lowered plane and are connected to said raised plane, each buoyant portion defining: - a first inner volume with a first height (h 1), designed to remain below the waterline as soon as the bulb or seedling to be cultivated is placed in the cultivation cell, - a second inner volume with a second height (h 2), configured to remain above the waterline when the bulb or seedling to be cultivated is placed in the cultivation cell and to sink below the waterline completely when the bulb or seedling to be cultivated has become a mature plant, - a third inner volume with a third height (h 3), configured to remain above the waterline when the bulb or seedling to be cultivated has become a mature plant; - a first inner volume with a first height (h 1), designed to remain below the waterline as soon as the bulb or seedling to be cultivated is placed in the cultivation cell, - a second inner volume with a second height (h 2), configured to remain above the waterline when the bulb or seedling to be cultivated is placed in the cultivation cell and to sink below the waterline completely when the bulb or seedling to be cultivated has become a mature plant, - a third inner volume with a third height (h 3), configured to remain above the waterline when the bulb or seedling to be cultivated has become a mature plant; the sum of said first height (h 1), second height (h 2) and third height (h 3) corresponding to a height of the side walls between said raised plane and said lowered plane and wherein said side walls extend as far at least one free edge of the single-piece tray and define a channel which communicates with a space outside the single-piece tray.