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Thread: Rock Wool Medium

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  1. #1
    Real Name
    Ray Barkalow
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    Oct 2012
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    Oak Island NC
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    Default Rock Wool Medium

    Over at another forum, there are folks that use Grodan rock wool cubes for their phrags, so I thought I'd get some to experiment with.





    Grodan is a long time manufacturer of inorganic rock wool horticultural media. This product is manufactured by melting basalt and spinning it into fibers, much as insulating fiberglass is made. The fibers are produced as a mat, then cut into smaller pieces for use. In this case, they're approximately 1 cm cubes. The fiber is approximately 50/50 hydrophilic/hydrophobic, so is supposed to remain fairly airy.


    I did a little experimenting:



    • I filled a container (roughly equivalent to a 6″ pot 6″ tall) with the dry cubes – they weighed only 2.25g.
    • They were soaked in RO water for 36 hours
    • Saturated, they weighed 308g. After 5 days of sitting open in warm, humid air, only 15% of the water had evaporated.
    • The saturated cubes occupied approximately 55% of the container volume, leaving 45% air space.
    • The pH of the soak water was 5.4, so should be fine right out of the box.
    • The EC was only 20 µS (for reference, a 100 ppm N solution of K-Lite has an EC of 710 µS).




    I am planning to experiment with my phals in a mix of LECA and cubes (75/25? 50/50?). I currently grow them in straight sphagnum, because the evaporative cooling in S/H pots in my home in winter cools them too much.


    I can conceive - based upon the water retention - that a blend will serve to "flatten" the moisture gradient in an S/H pot, keeping it moist to the top.


    If anyone else wishes to play with it, I have a few boxes available, so feel free to PM or email me.

  2. #2
    Real Name
    Bruce Brown
    My Grow Area
    Greenhouse
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    Cattleyas & Slippers
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    Mar 2003
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    Male
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    Arkansas
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    Default

    We tried this stuff and with our watering schedule, everything stayed too wet. I'm really happy using coconut husk to hold moisture as part of my potting mix.

    cheers,
    BD

  3. #3
    Real Name
    Ray Barkalow
    My Grow Area
    Porch/Patio.
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    Oct 2012
    Location
    Oak Island NC
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    1,989

    Default

    My experience in the old days was the same, but I think mixing it as a minor additive to something like LECA has merit.

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