| Hydroponics,
Gardening not Science
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A Description of Common Hydroponic Systems | |||||||||||
| General Principles and System Types | |||||||||||
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Hydroponic systems aim to provide plants with all they need in the right proportions at each stage of its life. To understand this it might help to look at how plants work and how that relates to hydroponics. Plants
use mineral nutrients from the soil, elements contained in water, carbon
dioxide from the air and sunlight to create the materials they needs to
grow.
Its roots seek out more nutrients as the plants grow by spreading
out through the soil. It must use some of the proteins it creates on
growing a large network of roots to sustain growth. In the end this is
what limits the plant. Each requires an area from which it extracts
nutrients, they must compete with other plants in the same area and may
have to extend their root network to get what they need. This is the
reason seed packets carry a minimum spacing recommendation. In
hydroponics the food and water are provided by the nutrient mix, soil is
replaced by substrate. Nutrients are continuously available and the
planting media’s open structure provides easy access to oxygen from
the air. The plants don’t have to work hard to get to the nutrients
they need, the nutrient comes to them and in just the right proportions.
The energy otherwise expended searching for nutrient can be used for
growth above ground, ultimately increasing crop yield. Artificial light
and heating can replace the sun’s light and warmth but in our set-up
these will be provided naturally to keep things simple and the costs
down.  A
typical hydroponics system includes a tank or container of some
description containing the nutrient mix, some have substrate to act as a
sponge to hold onto the nutrient for a while and act as support for the
plants, others support the plant directly with the roots exposed to the
nutrient. A pump is used as the means of getting the nutrient into
contact with the plant without the hard labour involved in watering and
feeding manually using watering cans. Discussed here are the various
ways of combining these components into a working system.
The
simplest hydroponic set-up can be made using a bucket with a hole in the
bottom. The bucket is filled with a free draining material that doesn't
contain organic substances that might alter the balance of the nutrient.
Sand, perlite, clay pebbles or rock wool can be used. A plant is
transferred to an open structured pot and planted in the media. The
nutrient is mixed and held in a watering can. This is used to water the
plant by hand as required. Another container is positioned below the
hole to catch any run-off. The
nutrient is held in the spaces between the media and used by the plant.
Its free draining nature also ensures that the plant doesn't get water
logged and has access to oxygen. This plus sunlight provide all it needs
for active growth. This
two-container system is the basis of most hydroponic systems and
although the buckets are replaced by receptacles of different shapes and
sizes, and the nutrient is recycled by a pump, the principles remains
the same. Hydroponic systems can be roughly classified into the following four groups:
These are discussed below. |
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| Aquaculture | |||||||||||
 This
utilises a reservoir of nutrient on which polystyrene rafts are floated.
The rafts are perforated with holes large enough to take an open
structured pot of 50-100mm diameter. The plants roots grow through the
open structure and are constantly immersed in the nutrient that is
aerated to keep it from stagnating. Fast growing crops such as lettuce
are often cultivated using this system. This technique is not best
suited to plants requiring longer to mature as root problems can be
caused by their constant immersion. |
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| Intermittent Flow | |||||||||||
 The
simple bucket system falls into this group, the intermittent flow being
provided by the action of the watering can. A more sophisticated example
of this system is Flood & Drain or Ebb & Flow. A container is
filled with a free-draining material and the plants either buried
directly in the substrate or in open structured pots. Pots give the
grower a little more flexibility in that plants can be moved as they get
larger or should the system need maintenance. The nutrient in this
system is periodically pumped into a container or tray, into which the
plants are placed, until it fills and reaches an overflow, submerging
the plants roots. It returns to the nutrient sump through the overflow.
After a short period of flooding the pump is switched off and the
nutrient in the plant filled container drains back down the pump outlet
leaving a small amount trapped in the gaps between the media. Fresh air
is also trapped. The cycle is repeated at intervals, the frequency of
which is determined by the requirements of the plant and choice of
substrate, infrequent flooding when the plant is small increasing as the
plant grows and is feeding more heavily. |
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| Continuous Flow | |||||||||||
 In
this system the nutrient solution is constantly pumped over the plant
roots. NFT or Nutrient Film Technique belongs to this group and is one
of the most common types of hydroponics. Systems vary tremendously in
construction from dual-flow Film and Mist rigs where the nutrient film
is augmented by misting in the upper section of the channel, to simple
systems made from rainwater pipes or plastic troughs. The plants are
often suspended in open structured pots in the pipes or channels down
which a shallow stream of nutrient flows. The depth is important, too
deep and the roots won't get the oxygen they need and will rot. The
fluid is returned from the end of the channels to the sump for
re-circulation. No inert media or substrate other than that in which the
plant was propagated is used.
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 Drip
or Pot Irrigation is another common Continuous Flow technique where
nutrient at much lower flow rates is dripped onto the media in which the
plants sit. If the balance of nutrient supply to plant use is very good
then there will be little nutrient mix returned to the sump and this
particular system can then be classed as Non-Circulating, but it's a
fine balance. Pots with granular media or rock wool slabs are used in
this technique. A steady supply of nutrient is available to the plant
and the low flow rate ensures that the media contains a large volume of
oxygen. The slab is particularly interesting. Laid in a tray at a slight
incline the plastic covered slab simply has slits cut into the underside
to act as drainage holes and openings cut in the upper side where
propagated plants are simply sat, allowing the roots to grow into the
slab. Drip irrigator fittings are pushed into the slab at intervals
supplying the plants with a constant flow of nutrient. The nutrient
returns to the sump through an outlet in the bottom of the tray.
Coco fibre slabs can also be used in the same way. |
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| Aeroponics | |||||||||||
 This
system is usually constructed from a single container. The top surface
is perforated with holes to take open structured pots so that the roots
hang into an air-space below. The roots are misted with a fine spray of
nutrient, either intermittently or continuously. The spray can be from a
simple sprinkler of from a more sophisticated electric fogger, which
provides a very fine mist. No media other than that which the plant was
propagated in is present. The
oxygen rich environment is particularly suitable for young plants with
developing root systems. |
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