To achieve good results, a home grower must
know about plant physiology. Plant physiology is the part of
biology which is concerned with the way plants grow and flower.
In this chapter, the priciples of plant physiology are discussed.
With the growth and flowering of plants, it involves a select
combination of light, air, and water. For light, it's about
sunlight for outside growing, a combination of sunlight and
artificial light for greenhouses, and just artificial light for
inside growing. For air, the amount of carbon dioxide (CO2) is of
principal importance. Water performs various functions. Plants
need water (H2O) for the growth process, but also to transport
other important materials.
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2.2. Principles of growth
Plants change CO2 and H2O into glucose under
the influence of light. Glucose is the chemical building block
for the structure and sturdiness of the plant. From glucose, the
plant makes cellulose, the material which gives plants their
fibrous structure. (Glucose is, in fact, stored light energy).
The chemical process in which carbon dioxide and water are
converted into glucose is called photosynthesis (from the Greek
'photos' = light, and 'synthesis' = to compose). Chlorophyll,
which also gives plants their green color, is indispensible for
this process. If all the conditions are right, the following
chemical reaction occurs:
We can deduce a number of things from this formula. To get one
part glucose, we need six parts CO2 and 12 parts H2O. It would
seem that less water is necessary. When we look at the chemical
formula, six parts water are also produced next to the 6 parts
oxygen, and 1 part glucose. However, research has shown that in
the chemical process, 12 parts water are needed. The 'excess'
water is used in the intermediate steps. The water does not
re-appear until the end of the process. CO2 is a gas in the
atmosphere. There must always be sufficient carbon dioxide
available, otherwise, plant growth will reduce. Everyone knows
that plants need water From CO2 and H2O, not only glucose, but
also oxygen is made under the influence of light, by the plants
with the help of chlorophyll. For plants, Oxygen is a by-product
of growth. For people and most animals, it's the primary
condition of life. This is a good combination. In fact, in their
metabolism, animals do the converse of what plants do. They
convert glucose and oxygen into carbon dioxide and water to be
able to move, and to allow the heart and lungs to work, etc. CO2,
a gas which is exhaled by people, can again be used by plants for
photosynthesis. It can be thought of as a cycle. The glucose made
by plants is an energy source for the plant. Some processes, such
as the intake of water, require energy. Next to that, glucose
forms the building material for all kinds of other processes with
which the plant lets all its specific properties show. It would
go to far beyond the pupose of this book to look into all those
chemical processes. For the reader of this book, it's about
getting good results growing cannabis at home A plant cannot grow
without light, air (which contains CO2), water, and various
nutrients. The chemical process in which CO2 and H2O are
converted into glucose and oxygen under the influence of light is
called photosynthesis. When we look at this process a little
closer, it actually involves two different chemical reactions.
The first is called photolysis. In photolysis, water is broken
down into oxygen (O), and hydrogen (H). Both light and
chlorophyll are necessary for photolysis. This is called the
light response. The second chemical reaction is called the dark
response As the term suggests, no light is necessary for the dark
response. With dark response, carbon dioxide is converted into
glucose, with the help of the hydrogen produced during the light
response. The distinction between the light- and dark reaction is
of interest to the cannabis home grower in order to gain insight
into the manner in which the plants must be illuminated (and
sometimes kept in darkness). The plants grow optimally only when
a good balance is found between the light and dark reactions.
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2.3. Osmotic processes
With osmosis, we mean the processes in which
water and nutrients are absorbed by plants. Osmosis is based on
the principle that the plant's walls permit some materials to
pass through, and others not. Cell walls are semi-permeable. An
example: when we place a bladder with a sugar solution in a tank
of water, the bladder swells. The sugar solution attracts the
water. The more sugar in the solution in the bladder, the more
water will be absorbed, and the pressure in the bladder will
rise, but don't try this at home! Among other things, osmosis
provides for the sturdiness in plants' cells. So much water is
taken in that the plant cells become saturated, and the stalk and
the leaves stand upright. If too little water is in supply, the
plant cells give off the water; slowly, but surely. The strength
is lost, and the plant wiltsAnother way for a plant to lose its
sturdiness is for osmosis to work in the reverse direction. If
there is too high a concentration of materials in the water fed
to the plant, the plant will not absorb water. It will release
water, and become less sturdy. An example is the addition of too
high a dosage of fertilizer to plants. With over-fertilization,
plants dry out and burn . . . A second important function of
osmosis is the 'hitch-hiking' of salts (nutrients) together with
the water that, through osmosis, ends up in the plant cells.
Nutrients are necessary to allow certain growth processes to take
place. The salts also cause various kinds of plants to develop
various properties. That brings flowers, fruit, and fragrances to
mind. In general, plants need the following materials in a water
solution: - nitrogen, phosphorus, and sulphur for the
construction of cells; - magnesium to manufacture chlorophyll; -
potassium, calcium, and magnesium for osmotic processes; - water
for growth, for the transport of nutrients, and for sturdiness; -
iron, boron, copper, manganese, and zinc as building materials.
Most of the nutrients for plants are sufficiently present in our
ordinary tap water. But not all The law of minimums plays a great
role in the feeding of plants. Material that is present in too
small a quantity is a limiting factor on the plant's health.
So-called 'deficiency disease' appears when a plant does not
receive one or more nutrients. For example, a shortage of iron
causes rather white leaves, while a shortage of nitrogen causes
reduced growth and yellowed leaves. 'deficiency disease' involves
not only the direct effect (an unhealthy plant doesn't grow
well), but also impaired resistance. If needed materials are
lacking, the chance for infection by moulds and vermin increases.
We will discuss plant diseases more extensively in a later
chapter. In order to raise healthy plants, we need further
amplification of the materials which, by nature, appear in our
water. This involves primarily nitrogen (N), phosphate (P), and
potassium (K). A formulated combination of these materials is
available in shops, and is called 'NPK solution'. We
differentiate the different nutrients in order of importance. We
call the most important the primary nutrients; - the NPK
combination just mentioned. The secondary nutrients follow;
namely magnesium (Mg), and calcium (Ca). Finally, there is a
group of micro-nutrients, also called trace elements. Sulphur
(S), iron (Fe), manganese (Ma), boron (B), zinc (Zn), and copper
(Cu) belong to this group, among others.
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2.4. Intake and transport of materials
Water, and the nutrients dissolved in it
(salts), is absorbed through the root hairs of the plant. The
condition of the soil plays an important role. Hard dirt allows
little space for water to reach the root hairs, a looser soil has
much more space, while rockwool substrate can guarantee a good
water supply. Root hairs are very important. When they don't work
well, the plant receives too little water and food. Growth is
retarded. Root hairs are very sensitive; they can easily be
damaged by exposure to air and light. Moreover, you can ruin them
by careless transplanting, or just by exposure. The intake of
water and nutrients requires energy from the plant, so oxygen and
glucose are necessary. Ultimately, temperature is a limiting
factor. Even if you take care to provide sufficient water and
nutrients, the growth of the plant will be impeded if the ground
temperature is too low. This is one of the reasons why most
plants outside grow very slowly during the winter. The transport
of water and nutrients insures that these materials end up in the
leaves. Two forces are responsible for this: the suction power of
the leaves, (they lose moisture by evaporation, causing suc-tion
to occur), and so-called root pressure. Root pressure can be
observed when we cut off a branch of a tree in the spring.
Moisture comes from the 'wound', and we call this the plant's
sap. The suction force of the leaves depends on the evaporation
of water through the leaves. Stomata are responsible for this
evaporation process. The stomata can open and close. Next to the
evaporation of water, they provide principally for the intake of
carbon dioxide (CO2) from the air. They also issue the oxygen
which is produced. In the previous paragraph, we have seen that
plants lose their sturdiness if they lose too much water. The
stomata dispose of a mechanism to prevent that: they can close.
Generally, a stoma will be open if there is light, (thus
providing for CO2 intake, and for optimal suction power of the
leaves), and closed if it's dark (when no CO2-intake, or
evaporation is necessary). If the air is extremely dry (dry, hot,
mid-summer days!), the stomata can also close during the day. For
stomata to work properly, a clean surroundings is necessary,
since a stoma can become blocked with dirt particles. Sufficient
potassium (nutrients!) are also needed.
2.5. Factors influencing the growth of plants
We conclude this chapter with a summ-up of the
principal concerns for the optimal growth and flowering of
plants. The following factors are the most important ones: - the
correct temperature; - the correct CO2 content in the air; - the
correct light intensity, with the correct wavelength of the
light; -the correct amount of water and nutrients - the right
soil; - (for cannabis growers) the right seeds or
cuttings/clones; - 'green fingers' In the second part of this
book, we discuss which materials you need for growing at home. We
take a deeper look into the different factors which influence
growth and flowering. Summing up this comes down to an optimal
control of climate.
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