With the short description of plant physiology, we already looked
into the function of water in plants. Water has three functions:
it is a building material (together with CO2 and light energy,
glucose is produced), it makes the plant sturdy (the plant cells
fill themselves with water, giving the plant a firm structure),
and it transports nutrients throughout the plant. Water is
indispensable for the existence of plants. Remember that the law
of minimums plays a crucial role here also: too little water, but
sufficient light, CO2, and nutrients, produces unfit plants. Too
much water, with respect to the other criteria, produces just as
poor results. Therefore it's important to find an optimal
balance, so the plants will flourish.
6.2. Water quality
It probably goes without saying, but the water you use must be as
clean as possible. For plants, however, 'clean' is a relative
concept. Nutrients such as nitrogen, phosphate, potassium, etc.
are always dissolved in water used for plant food. In any case,
the concentrations the plants need of these materials make the
water undrinkable for humans. In contrast to 100% distilled
water, 'pollutants' are found in ordinary tap water. You can
request a chart with data about the quality from the company that
produces your drinking water. The hardness in degrees - the GH
(German Hardness) - is also given. This is a measure for the
amount of calcium in the water. Below, you have an example of
this kind of water chart. Some of the 'pollutants' aren't
'pollutants' to plants, but actually fertilizing materials. To
determine the water quality (and the plant foods you add), you
need two types of meters. The first is an EC meter. 'EC' is the
abbreviation for 'Electrical Conductivity'. Pure water, also
called demineralized water, does not conduct electricity. When we
add fertilizer to the water, or the water is 'polluted' in some
other way, the water will indeed conduct electricity.
Fortunately, home growers can make use of this property of water.
With the EC meter, we can determine whether or not the
concentration of nutrients in the water will provide for optimum
plant growth. A high EC value means a high concentration of
fertilizing materials, and a low EC value, a low concentration.
Too high a concentration shows that you're over-fertilizing. As a
result, your plants will dry out and burn. (By osmotic processes,
water is drawn out of the plant; the leaves curl upwards or
downwards.) The fertilizer concentration must be lowered by
further diluting with water. Too low an EC value means a shortage
of fertilizer. This decreases the growth on rockwool substrate.
The EC value is given in millisiemens. 1.8 millisiemens is the
optimal value for growing cannabis. The second type of meter is
the pH meter. With a pH meter, you can determine the acidity of
water. Most of us have measured the acidity of a solution at one
time or another in high school. We did it with a litmus test. But
the litmus test is not suitable for measuring acidity when
growing hemp at home. The accuracy of this test leaves something
to be desired. Actually, we can only estimate the pH value, to
the accuracy of one pH point. We need greater accuracy for
cultivating cannabis. The average pH meter used by aquarium
owners is relatively cheap, and meets the requirements well.
Generally, they're up to 0.02 pH points accurate. The ability to
absorb nutrients depends on the acidity of the water. If the pH
is too high or too low, the plants can't absorb some nutrients
properly. Then deficiency disease occurs . The pH scale goes from
1 to 14. A solution with a pH between 1 and 7 is called 'acid', a
pH of 7 is called neutral, and between 7 and 14, 'basic'. The
lower the pH, the more acidic the solution (in our case: water).
On the next page, you have a chart showing which nutrients plants
can absorb best at each pH. You can read from the chart that
cannabis plants like it if they receive water which is slightly
acidic. The home grower must make sure that the pH of the water
being used is approximately 5.8. The EC meter, as well as the pH
meter, must be adjusted now and then. Special calibrating fluids
are available for this operation. The temperature is also an
important factor when calibrating an EC meter. The correct
temperature is listed on the package of calibrating fluid. A pH
meter has two set screws, and it must be adjusted to two values.
The probe of the pH meter is first dipped into a calibrating
fluid with a pH value of 7.0. Then, this value is set using one
of the set screws. After that, the probe must be cleaned well;
otherwise, deviations will occur with the second calibration.
Next, the probe is dipped in a calibrating fluid with a pH value
of 4.0, and this value is set using the other set screw. It's
important that the pH meter probe is kept moist. Depending on the
type of pH meter, it may be stored in ordinary tap water, or in a
special fluid supplied by the manufacturer. In the story about
the EC meter, we've already indicated that the temperature of the
nutrient solution influences plant growth. Cannabis grows best
with a water temperature of 25 degrees Celsius. Below this
temperature, the roots of the plant have more trouble taking up
water and nutrients. Too high a temperature is not good either.
That will kill the plants Tap water must be warmed up to 25
degrees C. Use a water thermometer to keep an eye on the water
temperature. Warming the water is easy with the installation of a
heating element in the nutrient tank. This equipment also comes
from the aquarium world. Quality heating elements with
thermostats are available for aquariums. For a 100 liter nutrient
tank, you need a 100 Watt heating element; with a 200 liter tank,
we recommend a 250 Watt element. Make sure the heating element is
always kept under water; otherwise it will be destroyed. This
means that you must never pump all the water out of the nutrient
tank to the plants. When you want to take the heating element out
of the water, always disconnect it first. Then, let it cool off
for at least 15 minutes. Only then can you carefully take it out
of the water. Any other way, you run the risk the element will
crack. To prevent algae growth in the nutrient tank, it's
important to add air to the water. We do that by means of an
aquarium pump with an aerator attached. The aerator is connected
to the pump, and placed at the bottom of the nutrient tank. The
water in the tank becomes rich in oxygen by aeration, and is also
kept in motion. This way, algae have much less chance to
proliferate.
6.3. The irrigation system
We do everything we can to promote plant growth. We provide
optimal lighting and sufficient CO2. As a third component,
regular irrigation is an essential link. This way the plants
receive their water and nutrients in time. The easiest way is to
water by hand several times a day. But, in the first place, that
involves carrying a lot of watering cans around, in which you've
dissolved the correct amount of fertilizer every time. In the
second place, watering by hand requires enormous discipline.
Giving water regularly on time will quickly 'water' YOU down You
can't skip a few days here and there, and leave your plants to
themselves. Finding a babysitter for cannabis plants is often
more difficult than finding a babysitter for your kids . . . So,
we prefer to give water regularly with an irrigation system
controlled by a timer clock. This way, we can rest assured the
plants get their wet and dry periods on time. In Chapter 3, we've
given a lot of attention to the installation of an irrigation
system. Now, we'll go a little deeper. In its simplest form, an
irrigation system consists of an immersible pump, controlled by a
timer clock, which has hoses with sprinklers attached to it. The
sump pump is placed in a nutrient tank with a capacity large
enough to make refilling necessary only two times per week. We're
talking about a tank with a contents of at least 25 liters per
square meter of garden space. 5 to 7 liters of water with
nutrients are used every day for each square meter. So, refilling
the tank every 3 or 4 days is enough. Remember, there must always
be enough water in the tank to cover the heating element and the
pump. Both instruments will be ruined if they are left without
water Preferably, the nutrient tank should sit on the floor.
There are two important reasons for this. In the first place, it
saves space. The tank can also be underneath the tables. In the
second place, it prevents the natural working regarding water
levels between communicating vessels. If the nutrient tank is
placed too high, the water will flow through the hose without the
aid of a pump. This goes on until the water level in the tank
reaches the same level as the lowest point of the connected
irrigation hose. Solutions can be devised for the problem of
'communicating' vessels; - coupling an electric faucet between
the nutrient tank and the irrigation hose, for example. This
solution is unnecessarily expensive. The problem of communicating
vessels can be prevented by placing a sprinkler outlet on the top
of the hose. The sump pump must be powerful enough to send water
to all the sprinklers that will be installed. For a garden 2 to
10 m2 in size an immersible pump with performance capability of 7
meters is enough, if used with a 1-inch irrigation hose. Also,
the pressure of the pump should not be too high, otherwise the
sprinklers (also called capillaries) won't drip, but spray Most
sprinklers function at a pressure from 0.5 bar on up. To the
immersible pump, we connect an irrigation hose (polyethylene or
PE- hose). The irrigation hose goes through the middle of the
grow trays. Then we make holes in the polyethylene hose and
insert the sprinklers. We install one sprinkler for every plant.
We have to prevent dirt and other materials from clogging up the
narrow openings of the sprinklers. We take two measures: first,
we keep a lid on the nutrienttank so nothing undesirable falls in
the water. Second, we place a filter between the pump and the
irrigation hose. In an ideal situation, plants should get water
and nutrients spread evenly throughout the day. We can arrange
for this by connecting a timer clock to the irrigation system. A
suitable timer clock must also have a minute setting, and must be
able to switch on and off at least 6 times a day. Modern timer
clocks are digital. These clocks have a memory to store the
desired times. If the electricity goes off, batteries usually
supply current to preserve the memory. The disadvantage is that
batteries run down. If the battery is dead, and the electricity
goes off, the memory is erased. The steady watering stops, and
the garden is damaged. The recommended choice is a timer clock
with a good car battery for backup. Now, our irrigation system
ensures that the plants get the correct amount of water and
fertilizer on time. The sprinklers evenly distribute the nutrient
solution. We prefer growing in 'libra trays'; - so-called
'growing trays' which have been especially designed for growing
on rockwool slabs. There are other methods, of course. You can
also lay rockwool slabs on corrugated roofing sheets, for
example. This does give problems with drainage water . It's more
hygienic, and more practical to work with growing trays. They're
not expensive, and it's simple to connect a drainage system to
them. Easier still is snapping drainage spouts onto the growing
trays. Then the water can be drained into a gutter. We divide the
irrigation of the plants into 6 periods during the 18-hour light
cycle. The first feeding takes place when the lights are switched
on. A feeding session follows every 3 hours, until 3 hours before
the lights go off again (the plants can take in nutrients only
during the light period!). In the beginning, we don't let the
irrigations periods last more than one minute, because otherwise,
problems with root development can occur. We stick to short
feeding periods. Throughout the entire vegetative phase. During
the generative phase (12-hour light cycle), we also divide the 6
feeding sessions so the plants will get water every two hours.
Since the plants have grown a little by then, and they need more
water, we let the irrigation periods last for two minutes. When
irrigating the plants, you must make sure the nutrient solutions
soaks through thoroughly. Thorough watering means that about
one-third of the water applied drains off. Thorough watering is
important to prevent the accumulation of the nutrient salts in
the rockwool slabs. If watering is not sufficiently thorough,
it's sensible to raise the number of irrigation sessions.
Finally, another word about safety. Everyone knows that water and
electricity are equally related as water and fire. The sump pump,
as well as the thermostatic heating element, work with use
electric currency and under water. Use only equipment of wich you
are sure it is well-insulated. Moreover, it's sensible to
disconnect the plugs before you put your hands in the nutrient
tank. This can save you from a possibly shocking experience
a shocking
experience