The aim of a greenhouse is modification of the environment, to warrant improved conditions (with respect to field) for crop productivity. We start with a brief review of present knowledge about the effect of relevant climate factors on production, with particular attention to [sporadically] non-optimal temperatures, on the short- and long-term production processes. In the next section we consider the effect of a shelter (cover) and of its physical properties on the temperature within. We show that the energy balance makes it possible to determine the temperature within a passive greenhouse in given meteorological conditions, as it follows from two independent components: one solely determined by the radiative and thermal properties of the cover, the other only by the ventilation rate. In order to get the widest possible short-term management range, the properties of the cover should be selected through an analysis of the long-term climate. Short term management of temperature within this range is done through regulation of ventilation, once number, area, place and type of openings has been determined in such a way that enough ventilation is possible also in the conditions of maximum load. Particular attention is given to the effect of limited ventilation on carbon dioxide concentration inside the house, and on the consequences in terms of productivity. Thereafter we discuss the criteria on which a cost-benefit analysis of active vs passive greenhouses should be based. Finally, after a short introduction of the critical success factors of a horticultural holding, it is pointed out that the climate may be not the most important one, but certainly it is a factor with a large bearing on production costs. A careful analysis of the design parameters that affect conditions within a greenhouse makes it possible to select the most efficient combination, once the climatic conditions are known.
Keywords: temperature and production, passive greenhouses, climate management, spectral properties, ventilation