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Perched Water Table In Container

In a nut shell Perched Water Table (PWT) is the characteristic of a given soil to hold water and resist drainage. It is due to the combined effect of Cohesion, adhesion and capillary action.

PWT is independent of pot shape (height and with). Here is a picture to demonstrate the principle.

In the above picture various size of pots are filled with the same medium, and watered to saturation. After a while letting to drain they all will have up to equal height of water remaining and not draining.

This effect is dramatic in a short pot in which most seedlings are grown. If the media has a high PWT the seedlings' roots will be sitting in water most of the time. It does not matter how many and how big the drain holes are. As a result of oxygen deprivation root rotting can reult as known as damping off.

You can do an experiment with your potting mix and find out it PWT, using a clear solo cup, as shown in this picture.


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