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
Overkill (term) Overkill (term) Overkill is the use of excessive force or action that goes further than what is necessary to achieve its goal. It implies that, while the goal was accomplished, there was collateral damage as a result. It may be a literal term referring to physical damage, though it is also used in colloquial conversation as a metaphor. An example is killing an ant with a sledgehammer. "Overkill" is especially used to refer to a destructive nuclear capacity exceeding the amount needed to destroy an enemy. The term is attested from 1946 and was in common use during the Cold