...which can directly or indirectly influence the success of a grow system. These variables should be monitored and controlled if necessary.
- Temperature
The temperature of the growing environment should be controlled so plants do not suffer the effects of extreme temperatures. Most plants grow well between 20 - 28 °C; aim for a temperature in the middle of this range (ideally 24 - 25 °C).
A maximum/minimum thermometer is invaluable for determining for the temperature range of your growing environment. Rest the thermometer between the plants and reset the thermometer daily so you get maximum and minimum temperatures for the previous 24 hours.
- Lighting
Providing an adequate temperature range for your plants can be made easier using lighting in a system. Lighting often emits an adequate level of heat to keep the temperature within the recommended range.
However, if the environment becomes too warm connecting an extractor fan will usually reduce the temperature by at least a few degrees Celsius bringing the temperature back into the recommended range.
Specialist devices such at the Coolshade can blow cool air directly onto sodium or metal halide bulbs.
Diurnal (day and night) fluctuations in temperature should also be minimised; research has shown that large variations in day and night temperatures can adversely affect plant growth.
A heater connected via a thermostat can be used to stabilise the temperature; set the thermostat to come on when the temperature falls below 20 °C and to turn off when the temperature is above 28 °C.
Timers are invaluable for lighting systems. It's easy forget when to turn your lighting on or off. Timers help stablise the growing environment through consistent lighting times which can be easily controlled.
If a propane heater is used it will supply the plants with higher levels of carbon dioxide which is of extra benefit to the plant. Please note that CO2 can also be supplemented using other methods including CO2 tablets. See below.
- Humidity
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Whilst many tropical plants can benefit from high humidity, a growing environment whose humidity is high for extended periods can lead to problems with mould forming on the plants and surrounding area.
Grey mould (Botris), a common danger to plant development, thrives under conditions of high humidity and can spread quickly, ruining the crop. Fruits such as melons and strawberries are particularly susceptible to fungal attack and extra care should be taken to ensure that humidity is kept low.
This can be achieved by measuring the humidity levels of your growing environment using an inexpensive device known as a hydrometer. The hydrometer should ideally be positioned next to the Min and Max thermometer. Aim for around 50 % humidity for normal plant growing.
An extractor fan can be used to reduce humidity if necessary but be aware that the temperature of the growing environment will fall as a consequence. Keeping the growing environment dry reduces the potential for higher humidity levels. Water spillages and even standing top up buckets are all potential sources of evaporation.
- Carbon Dioxide Levels
Plants use carbon dioxide (CO2) in order to maintain growth. CO2 levels can be measured using inexpensive CO2 analysis kits which were once a viable method only for the professional. CO2 is measured in parts per million (ppm), and 300-350 ppm is regarded at the minimum requirement for good plant growth. Using a pump action syringe and analyser tubes, CO2 kits are quick and easy to use.
CO2 levels can drop to less than a third of the normal atmospheric level within an hour depending upon the rate of growth of a plant. When levels drop this low, plant growth ceases therefore the grower must ensure that adequate levels of CO2 are available to the plant. CO2 levels can be increased using an extractor fan or leaving a door or window open in the growing room; plants do not prosper in a 'sealed' environment. A more controlled method of maintaining CO2 levels is through the use of CO2 regulators and Gas Growth Generators.
CO2 regulators when used in conjunction with a time modulation unit (TMU) will release bursts of gas at preset intervals through a 'lay flat' gas delivery pipe. The gas is contained in a gas canister and then released via the regulator. These are simple and efficient devices.
Of a more complex nature, Gas Growth Generators can increase CO2 levels by an amazing amount. They are a CO2 production unit designed specifically for a greenhouse or grow room and burn propane gas to produce CO2. Controlled by an electric solenoid connected to a timer, the generator can be timed to coincide with the light cycle enabling the plant to fully utilise the benefits of the higher CO2 levels. Of sturdy construction, the Gas Growth Generator is made of high grade stainless steel and is able to withstand many years of use in a humid environment. Although it burns gas, heat emitted is kept to a minimum whilst CO2 emissions are kept to a maximum.
Indeed many growers who use this method maintain CO2 levels above 1500 ppm and experience excellent plant growth providing the other requirements such as lighting, nutrition and moisture are adhered to. Plants which experience higher levels of CO2 tend to have darker leaves as the level of photosynthesis rises. Darkening of the leaves means the plant can absorb more light and so the efficiency of this process when used with the Gas Growth Generator increases further. Gas Growth Generators do not need to burn constantly to achieve a high level of CO2 in the growing environment.
Carbon Dioxide levels can also be increased be raised using CO2 tablets.
- Negative Ions
Ions are electrically charged particles formed through loss or gain of electrons by an atom. A negative ion generator installed in the grow room or greenhouse generates billions of negatively charged ions which help freshen and revitalise the surrounding air. They have been proven to have positive effects on plant growth and reduce the smell of foliage in your house if the grow room is contained within it.
Being inexpensive to both buy and run, negative ion generators can be put to a multitude of uses. They are often used in households to remove dust, smoke, pollen and bacteria. Individuals who suffer from hay fever would benefit from one of these devices installed in their household and place of work.
- Odour
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Some plants have a strong odour. Unwanted odour can be controlled using carbon filters, sprays and adequate ventilation.
