The Invisible Language of Plants
Plants don’t read thermometers. They don’t respond to temperature alone, or humidity alone. They respond to the relationship between them — specifically, to the difference between the vapour pressure of water inside their leaves and the vapour pressure of the surrounding air. That difference has a name. Professional growers have used it for decades. Most small-scale horticulturalists have never encountered it. It’s called Vapour Pressure Deficit, and understanding it changes how you see every plant you’ve ever grown.
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