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
The Water Is Wide (song) The Water Is Wide (song) "The Water Is Wide" (also called "O Waly, Waly" or simply "Waly, Waly") is a folk song of Scottish origin, based on lyrics that partly date to the 1600s. It remains popular in the 21st century. Cecil Sharp published the song in "Folk Songs From Somerset" (1906). It is related to Child Ballad 204 (Roud number 87), "Jamie Douglas", which in turn refers to the ostensibly unhappy first marriage of James Douglas, 2nd Marquis of Douglas to Lady Barbara Erskine. The imagery of the lyrics describes the challenges of love: "Love is handsome, love is