An apparatus for controlling the ethylene concentration in a crop storage facility for crops in the genera; solanum spp., allium spp., apiaceae spp., narcissis spp. or liliacae spp., the apparatus comprising an ethylene generator, an ethylene concentration sensor and an ethylene concentration controller, the ethylene concentration controller being configured, in use, to be responsive to a signal from the ethylene concentration sensor, which signal corresponds to the ethylene concentration in the facility at any given time, to initiate the release of ethylene from the ethylene generator only when the signal indicates that the ethylene concentration has fallen below a pre-selected minimum desirable ethylene concentration in the facility and responsive to the signal from the ethylene concentration sensor to arrest the release of ethylene from the ethylene generator when the signal corresponds to an ethylene concentration greater than or equal to a pre-selected maximum ethylene concentration in the facility, thereby to maintain the ethylene concentration within a range defined by the pre-selected minimum and maximum desirable ethylene concentrations and wherein the ethylene generator comprises a source of ethylene precursor and a catalyst for catalysing the production of ethylene from the ethylene precursor, the ethylene controller being responsive to a signal from the ethylene concentration sensor to initiate or inhibit interaction between the catalyst and the ethylene precursor.