The plants breaking down of nutrients is not instant, but it's water and nutrient uptake are, more or less, exactly like a straw lol. That's why when you water an under watered plant they recover super quick. Ever seen hollow stems...

Looks like a straw to me. Dwc you also notice changes you make pretty much instantaneously. Salt buildup and lockout in soil effects this and is why you'll see slower reaction to your nutrient solution changes generally. Means the soil is fucked already lol. I really wish people would just figure out how to use nutrients and regimens correctly rather than thinking flushing out salt buildup due to your grower error is beneficial to the plant because of the action, not the reason.
If you nute the shit out of your plants and have crazy salt buildup you absolutely should flush your soil(not plants) to get rid of excess salts. But the idea of flushing a plant is pretty silly. Plants only take what they need from a balanced nutrient solution. And they definitely won't give you nutrients back. Lol. They won't take more or less unless you have over saturated nutrients or aren't feeding them.
I'm going to reference fruits here because I've never heard of anyone flushing fruits ever. And if you can't taste Chems in tomatoes or strawberries when you eat them and they aren't bad for you, I see no basis for the flushing argument with healthy, well-maintained plants.
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