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How does a 100-metre tree lift water without a pump?
💡 Tall trees move water not by pumping it up from below, but by evaporation at the leaves pulling a continuous, self-sticking column of water skyward.
A giant redwood can hoist water more than 100 metres from its roots to its topmost needles — with no heart, no pump, and no moving parts. The secret is that the tree doesn't push water up at all. It pulls it, using nothing but evaporating sunlight and the stubborn stickiness of water molecules.
Here's the trick. Water evaporating from tiny leaf pores called stomata tugs on the water just behind it. Because water molecules cling to each other through hydrogen bonding (a property called cohesion), that tug travels down an unbroken thread of water all the way to the roots. The result is a continuous column under tension — the water is literally being stretched, like an invisible rope wound up by the sun. This is the cohesion-tension theory.
This also explains a limit: if the pull gets too strong, the stretched water can snap and form air bubbles (cavitation), breaking the chain — which is one reason trees can't grow endlessly tall. Cut a stem and you don't stop a pump; you just let air rush in and release the tension.