Vapour-pressure deficit the plant may dry out and die. For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 and 0.95 kPa. In ecology, it is the difference between the actual water vapour pressure and the saturation water vapour pressure at a particular temperature. Unlike relative humidity, vapour-pressure deficit has a simple nearly straight-line relationship to the rate of evapotranspiration and other measures of evaporation. To compute the VPD, we need the ambient (greenhouse) air
Vapour Col Vapour Col Vapour Col is a col lying south of Stonethrow Ridge on the west side of Deception Island in the South Shetland Islands of Antarctica. The name given by the United Kingdom Antarctic Place-Names Committee (UK-APC) in 1959 originates from the fumaroles in the col. This is the only locality on Deception Island where there is a complete cross section through the stratigraphy of volcanic succession. A 148 tract of ice-free land rising steeply from the south-western shore of Deception Island to 340 m, and including Vapour Col, has been identified an Important Bird Area (IBA) by BirdLife International