How Water Works in Pots and in the Soil

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Soil in Pots

How does a pot work?

How does the potting mix behave inside a pot? Believe it or not, pots suspend water up in the air! They make water float in the air!

In a pot, the water drains to the bottom of the potting mix, and some of it stays there. That is, a layer of two or three centimetres of water at the bottom of the pot is stopped from draining away. This is called a perched water table. To demonstrate the point, Don dunked a sponge vertically into coloured water, then put it onto a cake cooling rack to drain. A layer of coloured water remained at the bottom of the sponge. This is why pots work so well.

That reservoir at the bottom of the pot is what keeps the plant alive. We took the same sponge and conducted the same experiment but held the sponge horizontally, the water drained to the same height, about 3cm but it’s now holding about 3 times more water than holding it the other way. So if you’ve got a pot that’s not very tall but is wide, it holds far more water for the plant.

An old husbands’ tale is that if you plant a plant in the ground, it won’t need as much water as it would if you planted it in a pot. Not true. We took our sponge again and placed it into the coloured water and put it on another sponge to replicate the ground, this lower sponge sucks the water out of the top sponge proving that your plant would dry out far more quickly when placed into the ground. 

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