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The Hydroponics Manual: The Growing Environment

The Hydroponics Manual: The Growing Environment

It is possible to set up an indoor growing area just about anywhere in your house, shed or garage. Here are a few suggestions of places that might be suitable and point out some of the plant’s essential needs that must be taken into account when setting up.

To understand just what your plants require, imagine a sunny corner of the garden on a calm summer’s day. Most plants will grow well in the conditions that prevail on an English summer’s day and these are the conditions that need to be recreated in an indoor growing area. To simplify the growing, conditions have been grouped under the four headings of:


Light is the single most important thing for you to consider. Obviously, if you wish to grow plants in your coal cellar for instance, you will have to provide all the light yourself and you will need to provide a lot if you are to recreate the conditions of a summer's day. Fortunately, modern horticultural lighting is more than capable of doing this in an efficient and cost effective manner.

One can start by assuming that you have no natural light whatsoever in your chosen growing area. Obviously, if you have a window or skylight, this will reduce the amount of light that you have to provide but in most cases, this is not especially significant. There are other problems associated with using natural light, such as the inability to control the hours of darkness. The easiest and most efficient way to grow plants indoors is to do it in a dark area and provide all the light yourself. For greenhouse growers, the need to use extra light is limited to the darker months of the year.

If you want more information then a book such as "Gardening Indoors" which covers the subject fully is recommended.

Another thing to consider under the heading of light is the level of reflection in your growing area. A well designed grow room will get the maximum benefit from the light that is used in it and it is of great importance to get the best reflection of available light.


Temperature is another important design parameter of your grow room and it is something that must be borne in mind from the beginning. Most plant species will grow most effectively in the temperature range of 20-28°C, the mid twenties being optimal. It will not be difficult to maintain this sort of temperature in your room while the lights are on as they are a great source of heat as well as light. If temperatures should become too high, a simple extractor fan should serve to reduce them. This extractor can be easily linked to a thermostat to ensure that your room never reaches the high temperatures that can have a negative effect on growth rates. When your lights are off, however, you can expect a gradual decline in temperatures. In the colder parts of the year, they will drop well below the ideal growth range. Recent research has shown that night cycle temperatures are just as significant as day cycle temperatures in plant production and it is in fact the relationship between them that has most effect on the final shape and productivity of the plant. It is important to avoid large temperature fluctuations between the day and night cycles as this can lead to weak and poorly formed plants. It is ideal for most species to try and bring day and night temperatures as close together as possible and this is not as difficult as it sounds.

The most effective way to do this is to install a propane heater in your room and ensure that the thermostat is set to come on when temperature falls below 20°C and to go off at around 30°C. This device will work in perfect harmony with your lights which are the other source of heat in the room, and the extractor to maintain a constant temperature in the mid twenties. The added bonus of a propane heater is that it will produce copious quantities of carbon dioxide, the "growth" gas that will have an amazing effect on plant growth.

One of the cheapest and most important pieces of equipment in the growroom in the maximum-minimum thermometer. This should always be placed amongst the plants and consulted and reset daily. It will tell you the highest and lowest temperatures reached during the previous 24 hours.

Once you are established, it will be a simple matter to adjust your equipment to maintain the even and constant temperature that you are aiming for. If the maximum temperature is getting too high you adjust the thermostat or timer on your extractor. If the minimum temperature is getting too low, you adjust the thermostat on your propane heater.

The whole principle of indoor gardening is about control of the environment. This is your chance to tame the weather and the extra effort will be well rewarded by your results. An even better way of monitoring your growing environment is with a thermo-hygrometer. It can be switched on and left in the growing area for a period of 24 hours or longer. It gives clear and accurate readings of both temperature and humidity and it will also tell you the maximum and minimum levels of temperature and humidity over a given period. This is essential information for the serious grower.


Humidity is another important consideration in grow room management. If it is allowed to get too high for prolonged periods, it will cause problems both in your room and amongst your plants. The main danger is the development of Botrytis or grey mould amongst the flowers or fruit. This organism thrives in conditions of high humidity and will quickly spread and ruin a crop. Plants of the melon family and strawberries are particularly susceptible to fungal diseases and should be provided with a dry environment. The cautious grower will always monitor the humidity in his grow room which is measured by another simple device called a hygrometer. This is a dial type instrument that can be mounted on the wall next to the Max-Min thermometer and will give a constant and accurate reading of humidity. The ideal humidity for normal plant raising would not be much above 50%. If it rises above this, the grower will normally operate his extractor fan until it has been reduced. To keep this potential problem under check, it is advisable to avoid leaving water on the floor which can then evaporate and raise humidity. Any water or nutrient solution that spills or overflows should be wiped up promptly and nutrient tanks should be covered at all times. Any water that is left exposed to the heat from your grow lights will rapidly evaporate and add to the humidity levels. Keep your greenhouse or grow room dry.


The fourth variable that needs to be taken into account at the design stage is the atmosphere or air in the grow room and it is here the grower is often faced with a dilemma. On the one hand there is a strong requirement for a continuous supply of fresh air. Growing plants need a constant supply of carbon dioxide to maintain growth. CO2 is present in normal fresh air at the rate of around 330 parts per million (ppm). If you try to grow plants in a closed and sealed room you will quickly run into problems. As the plants grow they will rapidly use up the available CO2 which can drop to less than a third of normal levels within one hour. At this point, plant growth will effectively cease. To maintain normal atmospheric levels of this essential gas, the grower would be advised to run an extractor continuously as well as providing an input point, such as an open door or window, for the fresh air to enter the room. The problem with this of course is that the extractor will reduce temperatures and the grower may not wish to run it any more than necessary to maintain temperatures in the desired zone. It may also not be convenient to leave a door or window open on a long term basis. Fortunately, modern technology has provided simple answers to the grower's dilemma as carbon dioxide can be added to the atmosphere in the grow room which reduces the need for fresh air being brought in. CO2 can be introduced from bottles which can be rented from Esoteric Hydroponics, or it can be produced by burning propane.

Gas from Bottles

CO2 is readily available anywhere as it has many uses in the food industry including the pressurisation of beer kegs. This bottled gas is available in various sizes and the medium size is easiest to handle; avoid the largest ones particularly if you have to take them upstairs. It may be possible to get your gas in aluminium cylinders which are much lighter to handle.

Once you have your gas bottle you will need a regulator to control the amount of gas that enters the room, once again technology has the answer. There are various regulators and controllers that have been developed to provide simple CO2 injection for the amateur and professional gardener alike. These simple and efficient units will inject CO2 into the greenhouse or grow room.

Growth Gas Generator

This is a dedicated carbon dioxide production unit designed specifically for the small domestic greenhouse or indoor growing area. It burns readily available propane gas to produce carbon dioxide in copious quantities.

Growth Gas Generator is controlled by an electric solenoid and can be simply plugged into a timer. This means that the grower can easily set his generator to provide CO2 during the hours of brightest sunlight when plants can best utilise it. Generator can also be used with CO2 sensors to maintain precise levels in the hi-tech growing environment.

Growth Gas Generator is provided with suggested timer settings to provide optimum CO2 levels in any area up to about 43 sq meters. It is designed specifically for gas production rather than heat. Heat production is kept to a minimum for the volume of gas produced. The Growth Gas Generator is constructed from high grade stainless steel and is designed to last for many years in the humid environment of a greenhouse or grow room.

Growth Gas Generator is not a greenhouse heater. Greenhouse heaters are designed to produce heat, and carbon dioxide is merely a by-product. As they are thermostatically controlled they will produce more gas as the temperature drops. Unfortunately, this means that most of the CO2 is produced at night when plants cannot make use of it. Growth Gas Generator is designed to produce CO2 and can be set to produce it during the daylight hours. While it is a minimum requirement for good growth that CO2 should be in the range of 300-350 ppm, it is possible to provide it at much higher levels. Modern research has shown that levels up to 1500 ppm and beyond can be maintained in a grow room and that plants will respond amazingly well provided that they have adequate light, moisture and nutrition to enable them to take advantage of the conditions.

The serious grower who couples the power of modern horticultural lighting with the simple science of hydroponics and the benefits of enhanced CO2 can achieve growth rates and yields that were only dreamt of a decade ago.

Measuring CO2 Levels

Until recently, there was no simple way for the amateur grower to measure the CO2 levels in his greenhouse or grow room; it was only professionals that had the necessary equipment. Nowadays it is an easy matter with the CO2 analysis kit and there is no reason for the grower to rely on guesswork any more.

CO2 detection is easy with the pump action analyser syringe and analyser tubes measuring 300-5000 ppm. Quick measurement of CO2 in the grow room will tell you if your environment is optimised. Supplied with full instructions, the kit is quick and easy to use and it will give you a reading in parts per million. The careful grower will treat CO2 as one of the most important elements in a successful growing area. It is not a difficult matter to optimise the levels and the dramatic improvement in plant performance and yields will certainly make the effort worthwhile.

Negative Ions

The final thing the grower will consider is the installation of a negative ion generator in the greenhouse or grow room. This is an unobtrusive device that costs little to buy and less to run. Negative ions freshen and revitalise the air with very low running costs and removes dust, cigarette smoke, pollen and bacteria. This appliance cleans the air of pollutant particles while creating billions of negative ions which freshen and revitalise the air. Negative ions have proven effects on plant growth and will have a positive effect on yields and quality. They will also help to eliminate unwanted foliage smells in your house.

Pest Control

This is a huge topic and way beyond the scope of this factsheet. We can however, focus on some of the pest problems most commonly encountered in the small greenhouse or indoor grow room.

The control of plant pests has always been a contentious issue and we would assume that the majority of serious growers would like to avoid the use of toxic chemicals wherever possible. Like every other aspect of plant raising, there have been many changes in recent years. These have been tested and fine-tuned by professional growers and are now becoming available to the amateur gardener. Amongst the new technologies, the idea of biologicial pest control must take pride of place. Like all great concepts, it is simple yet effective and is causing major changes to the way we do things. Biological pest control is one of the most exciting developments in modern horticulture and it offers a vision of a pesticide free future when man can use nature's own weapons to grow his food in an uncontaminated atmosphere and a cleaner, greener world. Basically, biological pest control involves the introduction of friendly creatures to combat the ones that do the damage. These creatures are known as predators because they feed on the pest at some stage in its life cycle. Here are 2 examples:

Two-spotted Mite (Spider Mites)

These little creatures, almost invisible to the naked eye, are undoubtedly the greatest menace to the grower. They are often unseen and unsuspected until their numbers are high and they can multiply at a devastating rate. If they find favourable conditions in the greenhouse or indoor grow room they can literally destroy a crop.

The first signs of their presence are small dead spots that appear in clusters on the affected leaves. This is followed by a general bronzing of the foliage and as the infestation increases, there will be visible deposits of fine webbing on the underside of leaves. Old fashioned methods of chemical control have never been successful for long as these creatures are very adept at developing resistance to each poison in turn. Man has responded by using ever more toxic chemicals to control them with an ever decreasing success rate. The side effects of this are the collateral destruction of hundreds of beneficial or neutral insects that would normally co-exist with the mites in some sort of balance.

The solution that biological pest control offers is the introduction of another mite called Phytoseiulus Persimilis which lives exclusively on two-spotted mites. If the population of pests is at a high level, the predator will multiply in relation to its food supply. Once the pest is reduced then the predator will begin to die out as well. A balance should then be achieved which will maintain the pest population at low levels, below the point at which they will cause visible damage. If the pests do begin to multiply beyond the predators' capacity to consume them, the grower can then make small adjustments to the environmental conditions (temperature and humidity) that will favour the predators over the pests. Predator mites are known commercially as SPIDEX and can be purchased at Esoteric Hydroponics.


Most gardeners will be familiar with these little flies that fly up in clouds when you disturb the affected foliage. They are a major pest of the commercial greenhouse industry and they can cause just as much damage in a hobby greenhouse. Once again, the chemical approach has failed utterly to control them and breeders of biological agents have come to the rescue. The predator of whitefly is a tiny wasp called Encarsia Formosa. This minute wasp is totally harmless to everything but whitefly. It bears no resemblance to wasps as we normally think of them but resembles a fruit fly, only much smaller. Encarsia is totally dependent upon whitefly for reproduction as it lays an egg in the whitefly larvae which then becomes the food source for the developing larvae of the wasp. This process effectively replaces a whitefly with a wasp which can then go on and lay more eggs. This predator of whitefly is sold under the trade name of En-Strip and is available from Esoteric Hydroponics.


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