On a pot plant nursery three cultivation tables are heated directly with mat heating and one cultivation table is heated indirectly with tube heating. At these four tables the effect is measured on the air temperature below the table, the pot temperature, the energy use and the crop growth of Dieffenbachia. The conclusion is, that with mat heating a lower air temperature can be held under cultivation table to achieve a certain pot temperature. It is estimated that with this lower air temperature 10-30% of heat is saved because less heat disappears to the soil. For Dieffenbachia, the greenhouse air temperature above the pot is more determining for crop development than the pot temperature is. It is expected, that the energy-saving effect of mat heating is larger for plants with a low growth point, for which the pot temperature has more effect on growth.