Abstract: A method for controlling the environmental conditions in the proximity of vegetation or crops in the cultivation of plants is described in which use is made of protective sheets comprising a large number of microperforations having each a protruded rim, said microperforations having a diameter between 50 and 2000 .mu.m and being present in a density of between 25 and 40000 microperforations per cm.sup.2. The invention also relates to plastics sheeting for use in said method and to a protective device for use in a greenhouse provided with such sheeting.