Chapter 6: Water
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
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