| Hydroponics,
Gardening not Science
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Media or Substrate | |||||||||||
| Soil Substitute | |||||||||||
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In
some hydroponic systems, such as Flood & Drain or Drip Irrigation, a
substitute for soil is used to hold onto the nutrient briefly so that it
is available to the roots and to act as a support for the plant.
This media or substrate must be chemically inactive or inert so
that it doesn't change the fertilizing nutrient or have any local effect
on the roots. It must also be free-draining so that the roots don't get
water logged and start to rot but at the same time have a texture that
allows nutrient and air to stay trapped within it so that it is
available to the plant. It must also retain its integrity so that it
doesn't turn into a soggy mess. There
are a number of suitable media commonly available, rock wool, expanded
clay pebbles, vermiculite, perlite and coco fibre are often used. Sand,
volcanic tufa rock gravel and even marbles can be used but are less
common due to weight or their limited reusability. |
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| Rock Wool | |||||||||||
 This
media is made from molten rock that has been spun into fibres and
reconstructed into slabs. Sold in slab or cut cube form this is probably
the most popular hydroponic propagation material due to its moisture
retaining properties and the fact that even when completely wet it still
manages to trap about 20% of air for its volume. After propagation, rock
wool be used for potting-on. This is simply a matter of inserting the
small propagator sized cube into a larger one with a pre-cut hole. Rock
wool can be reused but the root mat that grows into the media make this
impractical for more than a couple of seasons. |
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| Expanded Clay | |||||||||||
 As
the name implies this material is made from heat treated clay pellets.
When heated, trapped air in the clay expands forming a honeycomb of tiny
bubbles inside the pellet. The pellets cool to form lightweight pebbles
with excellent moisture and air retaining properties. These are a
favourite soil replacement substrate and can be used in almost all
hydroponic systems. Being especially good at providing firm anchor for
roots this substrate is capable of supporting plants without additional
help. Once the plants have been harvested the clay pebbles can be
recovered, cleaned and reused easily. |
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| Vermiculite | |||||||||||
 A
mineral resembling mica is heated causing it to expand to many times its
original size. This has excellent insulation properties making it good
as a propagation media. It also has a good moisture retaining ability,
too good in fact for it to be used alone for growing plants on, as water
logging can be an issue. This is improved by mixing the vermiculite with
other media such as perlite in 50/50 proportions. |
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| Perlite | |||||||||||
 Another
heat treated mineral, this time volcanic in origin. It's very light and
has very good moisture and air retaining qualities. Perlite is often
mixed with soil to prevent compaction in conventional growing so makes
an ideal partner for vermiculite. Perlite can be used right through the
grow cycle and is a favourite in Drip Irrigation systems. |
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| Coco Fibre | |||||||||||
 This
coarse media is made from coconut husks. Coco fibre is treated to remove
organic salts and then packaged as loose fibre or slightly compressed
slabs. The fibre has an open texture providing spaces for nutrient and
air. Not commonly used as a propagation media but for growing on in Drip
Irrigation systems. |
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