Units and system for hydroponics

An improved unit for hydroponics. The unit comprises a covered trough (1) holding a body of nutrient solution (9) with an air space above it, means (12, 13) for continuous injection of nutrient solution in atomised form into the air space, plant holders (17) pentrating into the trough (1) trough the cover (2) and adapted each to hold the lower stalk portion of a growing plant such that the lower stalk end is at or above the surface level of the nutrient solution while the roots depend into the solution, adjustable overflow means being provided for the continuous discharge of the solution from the trough (1). There is also provided a hydroponics installation comprising at least one such unit. Furthermore, there are provided plant holders (17) for use in the unit.