The method involves exposing crop plants to gas atmosphere comprising carbon dioxide in volume portion of 0 to 5.000 parts per million by volume and ethylene in a volume portion of 1 to 50 parts per million by volume, in a greenhouse (1). The ethylene and/or the carbon dioxide are introduced by using a gas distributor (3) and/or using nitrogen. A gas mixture of ethylene, carbon dioxide and/or nitrogen is used for creation of gas atmosphere. The carbon dioxide is provided in the gas atmosphere by incineration. Independent claims are also included for the following: (1) a gas mixture (2) an aeration system.
