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Expanded Shale

Commercial bonsai potting soil made with expanded shale. Wikimedia photo by Ragesoss


The results from this product have been fantastic and it works even better when used with the organic amendments and overall program. It is available in its basic form, mixed with compost and also in a non-peat moss potting soil with coconut fiber and compost.



EXPANDED SHALE: Made from natural and ground to 1” to ½” range particles and then kiln fired. As it progresses through the kiln for 40 minutes at 2,000 degrees C (3600F), certain chemical processes take place in the silica content (60-70%) causing the material to expand. As the material cools, cavities are left after gases escape, leaving a porous lightweight chunk capable of absorbing water and releasing it slowly at a later time.


Expanded shale is one name for this product that has a gardening application, but was initially put to use mixed with cement in making concrete. The related geological group (metamorphic slate, sedimentary shale, and clay) can be heated to transform into a light-weight porus product. Depending on the source and location, the generic term "expanded shale" goes by commercial names Haydite, Kenlite, Buildex, etc. Other horticultural uses include as a light-weight ingredient on green roofs.


I recommend it to be used along with other organic soil amendments to loosen and aerate soil. It is also an excellent potting soil ingredient, especially when used with shredded coconut fiber and compost.





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