Plant Support Systems
Growing Media
Hydroponics systems use substrates. A wide range of both familiar and
new substrates are being produced and promoted. There are organic and
inorganic types and naturally occurring and artificial types. Of the
naturally occurring substrates, some are used in their natural form and
some are processed. There are also a number based on recycled materials.
Some recycled media have proved to be phytotoxic to plants, due to
toxic products among the source materials. An example is nursery potting
mixes made from sewage sludge. Early batches of this medium had excessive
levels of toxic elements and compensation of many million dollars was paid
to growers whose plants died as a result.
The main medium used for hydroponics has been rockwool. Another medium
used extensively is peat, although most of this is used in the nursery pot
plant industry.
A much wider range of substrates are being used commercially. These
include plastic foam, processed wood substrates, perlite, pumice, peat,
coconut peat, and glass wool.
Different plant species are best grown with different support
systems
Plants need air as well as water around the roots. They need a healthy
root environment.
Plant roots do work and so consume oxygen which they must take in from
their local environment. A root environment devoid of oxygen will damage
or kill the plant. The roots of plants have mechanisms for getting
from the water in their vicinity the dissolved ions of all the nutrients a
plant needs. The plant can only obtain the nutrients that are actually
dissolved in water. Each mechanism has its own different efficiency. This
means that the optimum nutrient solution is different from the level of
ions inside the plant root. Each plant variety have different performances
and so require their own optimised solution for optimum growth.
The differences between different media affecting plants are the
 | Rockwool slab system. Molten rock spun into fine fibres. |
| Ebb and flood (water floods into container, then drains back to
reservoir). |
| Peat bag culture (similar to Rockwool slab, but uses peat as the
growing media). |
| Coconut seed Coir - the inner husk, or pericarp, of the coconut (low
cost and effective). |
| Vermiculite - hydrated magnesium aluminium iron silicate. It is
light and spongy. |
| Perlite - a processed mineral - it has no cation exchange capacity. |
| Sand - clean granitic or silica type sands (avoid alkaline sands). |
| Gravel - 2-15mm in diameter. |
| Scoria - porus volcanic rock. |
| Pumice - crushed salicaceous volcanic rock (often mixed with peat
and sand). |
| Expanded clay balls. Made from heating blended and bloated clay. |
| Sponge foams. Mostly used for propagation. |
| Expanded plastics. Inert and poor in water retention. |
| Sawdust. Hardwood sawdust should be composted. |
| Peat Moss dug from swampy ground in cool temperate climates. |
| Hanging bags of growing media with drippers feeding the
water/nutrients to the plant. |
