Perched Water Tables

nallred91November 13, 2011

With all my searching on perched water tables, I'm still unsure of a few things...

1) How can you identify a pwt in a container?

2) I know the pwt is said to disappear as the particle size reaches 1/8", so does that mean I could screen my turface with a 1/16" screen, then mix it with my growers sized gran-i-grit and have a mixture with no pwt? When screening turface over 1/8" screen I lose a lot of turface, so I'm hoping I can sick with screening over my regular 1/16" window screen and that the addition of grit will eliminate the pwt.

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This first mix is a mix of pea gravel and turface. I did screen the turface, but I'm not sure how I can check to see if there is a pwt in the bottom of the pot?

This mix is pea gravel, perlite, and bark. The particle size for these are pretty big, so I'm assuming no pwt. The plants have been happy and growing in this mix since late summer, so I assume there is no pwt. But I would still like to know for sure. Either way, I plan on repotting these two plants into probably a mix of turface and grit in the spring.

Here's another example of the turface/pea gravel. although here the pea gravel was a little dirty... But does the presence of the pea gravel here help to eliminate whatever pwt the turface may be causing?

And here's the granite I plan on mixing with turface for all of my future pottings. by the looks of it, i don't think screening it with a 1/16" screen would do much.

any advice would be great. Hopefully I'll figure out a simple way to get a turface/grit/perlite mix that doesn't hold a pwt.

    Bookmark   November 13, 2011 at 2:21PM
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tapla (mid-MI z5b-6a)

If almost all of your soil particulates are larger than 1/10", you don't have a PWT. You can also see if your soil has a pwt by filling a plastic glass with your soil then melting or drilling a hole in the bottom and allowing the free water to drain. You should be able to identify the ht of any PWT by observing any delineation between soil that's saturated near the bottom and soil that ISN'T saturated nearer the top. You'll be able to tell by observing the difference between air-filled pores & water filled-pores.


    Bookmark   November 13, 2011 at 6:26PM
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Ah thank you, I should have thought about that... that seems like a perfect way to check...

    Bookmark   November 15, 2011 at 2:49PM
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Thank you for providing this easy experiment. I used this mechanism to check as you stated above. However...I think I have significant perch water b/c:

1) when I drill hole in bottom to allow free water to drain...most drains that is "free water to drain"..but once it stops draining, I tilted the pot...even more water will drain (that means there is perched water right?)

2) I can't tell very well the delineation between the saturated and very saturated I also inserted a wick to see if more water will drain if I poke a tooth pick soil did not have extra water that drain due to the tooth pick insert...but did drain more (regardless of inserting tooth pick insert or not)...

Another question: how much perched water is significant trouble if I am using a regular 4in pot?


    Bookmark   November 15, 2011 at 7:05PM
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...ok...another dumb use the experiment big of the container must it be? I know from reading the forum that the PWT height will always be the same no matter what size of the container it is (Al's example with the funnel)...But I don't think I am understanding the concepts very well...

There must be at least 3in of soil in the container if the PWT height is 3inches right? how much soil should we have in how large of a container? I am confused...I am going to reread that thread again...maybe I will understand a little better?

    Bookmark   November 15, 2011 at 7:41PM
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