Osmosis – that magic process by which plants suck up the water from the soil. Wierd. Here’s a quick explanation:
In osmosis water moves from a more dilute solution to a less dilute solution through some kind of semi-permeable membrane.
Think of it as the way drivers will barge into the next lane over when it’s emptier. Water molecules are smarter than drivers though; they don’t keep doing it until the position is reversed, once equal dilution is reached the movement stops.
In a plant this starts at the root hairs with water being drawn from the soil into the plant through the cell wall. The water being drawn into the plant’s cells like this mantains their turgidity* and in non-woody plants provides much of the plants rigidity, which is why they collapse when they don’t have enough water.
It is possible to accidentally cause osmosis to work in the opposite direction to normal in a plant by feeding it a concentrated fertiliser when the soil is otherwise quite dry. This can push the levels of salts in the soil above the level of salts in the plant and when this happens osmosis starts to work in the opposite direction to normal; it starts drawing water out of the plant and into the soil. And that just sucks badly**.
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* The English language is great. It brings us words such as ‘turgid’. I’m going to be finding ways to sneak it into conversation all week.
** Sorry, couldn’t help myself.