Hydroponics Gardening - An Introduction To Hydroponics
Gardening For Beginners (Part 5) Plant Growth
By John R. Haughton
1 - Part
2 - Part
3 - Part
4 - Part 5
PLANT GROWTH & PHYSIOLOGY.
There are three classes of plants. Each of these classes
metabolize in a different way. The first class are succulent plants
called CAM. These plants like low light and high humidity levels and
so thrive indoors, in bathrooms and kitchen areas.
The second class of plants is called C4. These plants grow in
hot arid regions and are very efficient at using both Carbon Dioxide
(CO2) and Sunlight. Most C4 plants are grasses.
The third and last class of plants are called C3. These plants
join two 3-Carbon atoms together to produce sugar. The chemical
formula for sugar is C6H12O6 which is 6 Carbon, 12 Hydrogen and 6
Oxygen atoms stuck together. Most of our favorite plants are to be
found in this class.
HOW DOES A PLANT WORK?
Like all living things, plants breathe 24 hours a day. In order
to make energy each plant cell respires (converts plant sugar to
energy). The plant uses Oxygen (O2) and expires, or breathes out,
Carbon Dioxide (CO2).
In the same way that energy moves around the human body, so
water, nutrients and plant sugars are continually being transported
around the plant body. The leaves create a circular flow with the
roots. This circulation occurs when the leaves draw up, water from the
roots, through their Xylem.
These are straw like cells found in the plant stem. The water
continually evaporating from the leaves sucks up more water from the
roots and creates the internal water pressure that keeps the plant
rigid. Thus if the plant is deprived of water, as in a drought, it
loses its rigidity and begins to wilt when the internal pressure
The leaves return energy to the roots in the form of sugar
solutions. These are transported from the leaves via the plants
Phloem. These are also straw like cells found in the plant stem. In
this way the leaves exchange sugars for water and nutrients, while the
roots exchange water and nutrients for sugar solutions. This liquid
circulation is constant and continuous throughout the life of the
THE MAIN PLANT PARTS.
The 3 main parts of a plant are the Roots, the Stems and the
Leaves. Each of these parts is of great importance and any problem
that arises in any of them will be a major one. The most sensitive
part is the roots, as well as being the most difficult to see should a
The miracle of growth starts at the roots. As already
mentioned, roots transport nutrients up to their leaves and plant
sugars are returned by the leaves. The roots also act as storerooms
for the excess sugars that are produced by the leaves. These sugars
are stored in the form of starch. The size of the root ball and
therefore the amount of starch that can be stored, determines the
success of the plant in terms of growth and productivity.
The size of the root system is directly affected by the amount
of moisture, the temperature, the available Oxygen and the supply of
plant sugars being transported down from the leaves. According to
Graham Reinders, in his book “How to Supercharge Your Garden”, a
research Rye plant in a 12 inch pot was said to have had 14 billion
root hairs. These hairs would have stretched 6200 miles (nearly 10,000
km) if placed end to end and covered an area of 180ft by 180ft (about
55m by 55m). The greater the root system is the more energy (starch)
it will be able to store and so, the more nutrients it will be able to
send up to nourish the leaves. The plant will then have the capability
to grow stronger. The end result of this is that the leaves will be
able to pass more plant sugars back down to the roots and so the cycle
Another factor to be taken into account is the root medium.
Plants take their nourishment from the medium surrounding their roots.
It stands to reason that the less energy the plant has to expend in
order to get that nourishment the more energy it will have available
to use for growth and nutrient exchange with its leaves. Because a
plant takes most of its water in via its roots, (the root hairs
trapping the water molecules surrounding it) and transpires about 99%
of that water out via its leaves, it will wilt and fall over if its
roots cannot extract enough water out of its surrounding medium.
A plant growing in the ground will take its moisture from the
surrounding soil. This moisture normally gets into the soil as rain
and the plant absorbs that rain and the nutrients that have dissolved
in it, via its root hairs. After the rain has stopped the topsoil
quickly dries out as the water filters into the ground. Because of
this drying out the plant has developed a means of absorbing Oxygen
via its upper roots. The top third of the roots become specialized as
“Air Roots” while the bottom third becomes specialized as “Water
It is vital to ensure that the Air Roots are not kept constantly
wet as this will result in the plant drowning. The Water Roots
however, may be kept wet all the time, providing that the water has
sufficient Oxygen dissolved in it. Insufficient Oxygen will result in
roots with brown, discolored root tips and subsequent infections.
Healthy roots are a crisp, white looking structure.
The plant is quite capable of healthy living with the roots
exposed to light as long as they remain moist. However, light will
encourage the growth of Algae which will cause odors. The Algae will
also compete with the plant for Oxygen during the dark periods and
nutrients in the light ones. This, of course will mean the plant has
to work harder in order to produce sufficient sugars for its needs.
The Oxygen produced during the dark periods is used to help the roots
convert these sugars, from the leaves, into energy (Starch).
Copyright (C) 2004, 2005. J R Haughton. ITEC MIPTI --- All Rights
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