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Some of the mineral salts used in nutrient formulation tend to react with each other in concentration so nutrient solutions are usually formulated in an A and B (& C) pack and only mixed together in working solution. Keeping certain salts separate from each other means that the chemist has no restrictions and can supply exactly what the plant needs. Professional growers always use separate A and B (& C) tanks and it is now very easy for the home grower to maintain this professional standard.
Hydroponic systems can be divided into two distinct types and are usually termed passive and active systems.
A passive hydroponic system is one in which the nutrient solution is supplied to the plant periodically, usually by hand, and is allowed to sit in a reservoir of some sort to be used by the plant as needed. The simplest passive system is pot culture which is fully explained below. Passive systems are not favoured by commercial growers because of the difficulty of watering large numbers of plants. For smaller growers, they have a lot to offer as great results can be achieved with simple pot culture. The capital costs are usually much smaller too and there is less that can go wrong.
An active hydroponic system is one in which a pump is
used to supply the solution to the plants on a regular basis. The solution
is usually recirculated which is the most significant difference between
the systems in terms of management. Active systems can be divided into
several different types: rockwool, NFT, and Flood and Drain. All these
systems are well proven and they all have advantages in certain situations.
It will be up to the grower to decide which system suits his or her
purpose. All the major techniques will be examined in this paper with
the intention of helping the grower to decide which suits them best.
This is the simplest and safest way of growing in hydroponics. It is the true passive system, ideal for beginners but also favoured by experienced growers because remarkable results can be achieved with very little outlay. It is suitable for almost all types of plants and almost all growing situations. It is very cheap to set up and it is hard to fault it as an effective growing system.
Theory of Pot Culture
Pot culture is deceptively simple and it works due to the principle of capillarity. Basically, it is a simple matter of filling a pot with a suitable medium and supplying nutrient solution from a reservoir (saucer). The medium will bring the nutrient solution upwards by capillary action and maintain a constantly moist environment around the roots. Although the medium will always be moist, it will also retain a lot of air spaces around the roots. It is this combination of constant moisture, constantly available nutrients and high levels of air supply that make up the perfect root zone for optimum plant growth. This is what makes pot culture work so well.
The Pot or Container
The first step in pot culture is the choice of a suitable pot and saucer. Pots should always be plastic. If artificial light is used, you will want to use white pots if possible. The ideal size for larger plants, such as tomatoes would be around 15 litre capacity while a pot of about half that size will be useful for most small plants. The other requirement is a deep saucer to act as a reservoir beneath the pot. The popular Hydropot, available from most hydroponic dealers, is ideal for larger plants. It has a 13 litre capacity, is a brilliant reflective white and is supplied with a deep saucer. Hydropot is perfect for the cultivation of larger plants. For more information about pot culture, please see the section Simple Steps to Successful Pot Culture below.
For medium sized plants such as capiscums and most popular flowering plants there is a huge choice of suitable containers available at local garden centres. Just bear in mind that you need to maintain a reasonably deep reservoir at the bottom so look for saucers or trays to go with your pots. For small plants such as strawberries, herbs or salad vegetables, we would recommend plastic troughs which are available in a range of sizes. These troughs are also suitable containers for African violets, strawberries or virtually any small plants.
Having chosen a suitable pot or container you will need to fill it with a growing medium or soil substitute. The medium acts as an anchor for the roots and maintains a balance of moisture and air in the root zone. If it does this effectively then your pot culture will be successful so it is clear that choosing the right medium is of great importance. There are three main choices for pot culture and your choice will be determined by cost, availability and by the plants you plan to grow.
This is a great medium. It is cheap and lightweight and amazingly effective. Perlite is a naturally occurring volcanic rock that is treated in a furnace in a process known as exfoliation. Perlite is highly recommended because it has superb capillarity. Capillarity is the ability to lift moisture from a reservoir and it is the key to success with perlite. Perlite does have a tendancy to attract algae which will appear as a green stain on the surface. This is nothing to worry about but it is considered to be unsightly. An occasional sprinkling of clean dry perlite will keep it covered and under control. Perlite is by far the cheapest of the growing media and is available in 100 litre sacks from Esoteric Hydroponics.
This is a specially developed medium from Grodania in Denmark. It is blended from different types of rockwool to ensure the best possible ratio of moisture to air space in a growing medium. This is unquestionably the growing medium of the future. It will hold far more moisture than most other mediums, while still retaining plenty of air around the roots.
GreenMix is more expensive then perlite or clay pebbles
and may not therefore be viable for low value crops. For more valuable
plants such as orchids for instance, it may well be found to outperform
every other medium. GreenMix is now available from grow shops everywhere.
Please ask your dealer for more information. GreenMix for Orchids is
also now available as a drier, more aerated mix containing perlite.
This is highly suitable for the cultivation of orchids.
Expanded Clay (Clay Pebbles)
These pebbles are manufactured specifically for plant culture. They are lightweight and sterile and they have a distinct advantage over other media in that they are infinitely reusable. They are the perfect growing medium for house plants and almost anything in a small container and they are part of the hydro culture system which is designed for these plants. Clay pebbles are also available from Esoteric Hydroponics.
Never let the saucer dry out completely. It is advisable to flush your pots by water with plain tapwater until it runs out at the bottom of the pot, about every 4 weeks to remove any potential build up of salts.
To maintain your plants in pot culture is now very easy. All that you need is a good sized drum of nutrient solution and a watering can. Water your plants every 2 to 3 days. Try and ensure that the saucer does not dry out but avoid keeping it full all the time too. It is best to fill it just as it becomes empty which will allow maximum aeration of the root zone. It is possible to automate your pot culture system by placing drippers in each pot and using a pump on a timer. This is not usually recommended because each pot will require different amounts of nutrient so there will always be overflows. If you are growing in a greenhouse and have good control of the humidity levels, it may be possible to supply nutrient this way. For most situations, however, consider pot culture as a passive system that requires hand watering on a regular basis.
Nutrient should be supplied to the plants with a CF of around 2 mS/cm2 and a pH of 6. These values will be suitable throughout the crop but it is very important to check the solution in the reservoirs at least once a week. You may find the conductivity creeping up and when you do, it will be a very good idea to make up a barrel of pure water and use that for a few days until conductivity in saucers has been well reduced.
The Conductivity Truncheon is ideal for checking the solution in saucers. If it does get very high, it will be necessary to flush the entire crop. You will need to pass several litres of water through each pot to wash out the excess salts.
Pot Culture - GreenMix
Greenmix is a blend of mineral fibres in very exact proportions. Some of the fibres are water absorbent and the others water repellent. The result is a superb crumbly growing medium that combines the best characteristics of high aeration and good moisture retention to outperform any other soil substitute. The mixture is buffered with clay and lignite to ensure that a neutral pH is easily maintained. All the grower needs to do is water with a top quality nutrient solution such as Optimum.
Growing plants in greenmix is incredibly easy. In fact, in many respects, you treat it just like soil. Your new plants in wrapped cubes can easily be transplanted to greenmix as follows.
Recycling the Growing Medium
Perlite can be reused after one or two crops but it is advisable to flush it through very thoroughly and pick out all the old roots before replanting. Some authorities recommend sterlising old perlite with a weak solution of household bleach before reusing. Remember to flush thoroughly with fresh water afterwards. If you do decide to discard perlite, remember that it can be a valuable soil amendment and can be added to potting soils or dug into garden beds. Clay pebbles can be reused indefinitely and it is an easy matter to sterlise them with bleach between crops but remember to rinse them thoroughly. Greenmix is difficult to reuse and is probably best used as a valuable addition to potting soils or just dug into the garden beds.
Discarded lengths of PVC pipe are ideal for suspended planting of strawberries or herbs. Stormwater pipe (9cm diameter or larger) can be used in lengths up to about 1.5m. One end should be capped and a hole drilled in the side about 10 cm above the end cap. Planting holes can easily be made with a holesaw and should be evenly spaced around the outside of the pipe. Once the pipe is filled with a growing medium, the young plants can be carefully inserted through the holes into the medium. Once the pipe is suspended in a suitable location, the nutrient solution should be introduced into the top of the pipe by dripper hose or watering can until it runs out of the side hole, where it can be collected for reuse if necessary. This should be done 2 to 3 times a week. Watering will need to be more frequent with the suspended pipe if it is longer than one metre, perhaps once a day. This is because the medium at the top may be too far away from the reservoir to fully benefit from the capillarity of the perlite.
There are 3 basic types of hydroponic system in use by commercial growers and they are all adaptable to smaller scale for the hobby grower. They all have advantages and disadvantages and the choice of the individual grower will depend very much on their specific requirements. It is only possible here to offer an overview of these systems with the intention of helping the grower decide what suits their purpose. Esoteric Hydroponics stock a good range of books on commercial hydroponics and it is recommended that any grower contemplating an active system should read everything available on the subject.
This is the active system for handling plants in pots or other individual units. It is highly efficient and very easy to manage but it does require a bit of work initially to set up. The basis of Flood and Drain is a table with sides that can hold a certain level of nutrient solution. The solution should be pumped in on a regular basis and allowed to drain out as quickly as possible. The plants stand on the table in pots filled with a growing medium as in pot culture. The incoming nutrient will rise up from the bottom, flooding the roots and driving all the stale air from the root zone. As the nutrient level begins to go down, fresh oxygen-rich air will be drawn down from the top. It is this dynamic interaction of moisture and air in the root zone that makes Flood and Drain so effective.
The plumbing is quite simple but you need to ensure that nutrient will flow back through your submersible pump. Some pumps will not allow this and you will then need to install a bypass to ensure that nutrient can return to the tank and drain the table fully. It is very important to ensure that the table is completely level so that all pots receive the same amount of nutrient. The Future Garden and Nutriculture Flood and Drain Tables are tried and tested systems which have many refinements and are considered the most complete systems on the market today. Such tables can be obtained from Esoteric Hydroponics.
The best medium for Flood and Drain systems is undoubtedly clay pebbles. Pots should be flooded to at least one half of their total depth and this depth is set by the position of the overflow pipe. Flooding should be controlled by a timer on the pump but the emergency overflow outlet will allow this pump setting to be non-critical and will ensure that the table cannot overflow. Setting the timer will be a simple matter of timing the flood operation until nutrient is flowing out of the overflow. The pump should then come on for this length of time at least four times a day and up to twice an hour in very warm weather.
Important Points to Remember with Flood and Drain
The table needs to be very strong. Remember that water is very heavy so you will need to calculate the weight in your table when it is full and make sure that it is constructed strongly enough to hold it. The equation is very simple and can be expressed as:
Length × width × max depth (in cm) = volume in litres = weight in kilos (1 litre of water = 1 kilo)
You will need to cover the table and exclude light or you will have a lot of algae around the bottoms of the pots. A sheet of white / black / white plastic will be ideal and can be stretched tight across the table before the pots are placed on it. It is then a simple matter of cutting holes for the pots.
Flood and Drain will be improved if you warm and aerate the nutrient solution before supplying it to the plants. A simple aquarium heater will suffice to maintain the temperature of the solution - 18-22°C would be ideal. An aquarium airstone in the tank will help to ensure that the solution is carrying the maximum amount of dissolved oxygen which will certainly benefit plant growth. Oxy can be added to the tank at regular intervals to improve levels of available oxygen still further.
Flood and Drain can also be used with rockwool cubes. This is in fact one of the best ways of handling large numbers of plants. Due to the high level of fluid retention in this medium, however, there are slightly different guidelines for its use. In the first place, it will not be necessary to flood the table to any great depth, it is only required that the nutrient solution just touch the bottoms of the rockwool cubes. The table designed for rockwool cubes will therefore have the overflow pipe mounted much lower than for pots of expanded clay. Alternatively, the timer can be set for much shorter periods. It will be necessary to place the cubes on something such as plastic matting to raise them slightly off the table. This will allow excess moisture to drain downwards efficiently.
Good drainage is of crucial importance when using rockwool cubes on a Flood and Drain table. It is also very important to cover the table to exclude light. Once again, this can be achieved by stretching white plastic across the table. It is even more important with rockwool cubes to ensure that the table is completely level and therefore that all the plants receive the same amount of the nutrient solution.
Nutrient Film Technique is usually referred to as NFT. It involves the growing of plants in shallow streams of nutrient solution inside plastic gullies. It is a brilliant system and is now used widely for the cultivation of tomatoes and other large plants. It has also been adapted in recent years for the production of smaller plants such as lettuces and strawberries. The principles are the same but the size and layout of the gullies needs to reflect the final size of the plants being grown.
It will only be possible within the scope of this factsheet, to discuss the general principles as they apply to the smaller grower. For anyone contemplating using this system commercially, a recommended book on the subject would be the ABC of NFT by Alan Cooper.
The first step to NFT is finding a suitable channel. Steel is fine provided it is lined with plastic. The ideal width is 10cm for smaller plants and up to 20cm for large plants such as tomatoes and cucumbers. A single strip of white plastic film can be laid in the gully and then gathered up around the plants. Thus it serves as a liner and also as a cover to exclude light from the growing channels. This is the basic layout of modern commercial NFT systems and it will be seen how simple and cheap the system can be.
Once the plants are located in the channel, the nutrient solution should be introduced at the higher end and allowed to pass in a shallow stream down to the lower end where it is collected and returned to the tank. Although this is a very simple system, there are certain things to bear in mind before embarking on it. In the first place, the reservoir should be as large as practically possible. This is because the conductivity and pH of the solution will be changing all the time and a large reservoir will minimise the effects of this and reduce the number of times that you will need to check the solution. For commercial growers it is advisable to retain at least 2 litres of tank volume per plant in the system. For smaller operations, however that ratio should be increased to at least 3-5 litres per plant. The larger the reservoir, the better. It is also very important to ensure that the nutrient is sufficiently oxygenated. Fortunately this is very easy to achieve because there will be excess pumping capacity that can easily be diverted back to the tank.
In normal operation, valve B is kept completely open, allowing unrestricted supply of nutrient to the plants. Valve A is closed down just enough to give the desired flow rate at the gully ends. The solution that is still passing back to the tank should be sufficient to stir and agitate the tank vigorously and thus enrich the solution with oxygen. This layout of pump plumbing is very suitable for other systems such as rockwool cultivation.
NFT System Management
Once your system is running you will notice the rapid growth of a root mat in the nutrient channel. The bare roots are interfacing directly with the nutrient solution and this is the great strength and also a potential weakness of the NFT system. The direct contact between the roots and the solution makes for unparalleled growth and superb plant performance, provided that the nutrient solution fulfills the following requirements:
Once you have propagated your new plants in the SBS cubes, you can treat them in several different ways. If you wish to carry on growing in rockwool, then the next step will be to move the little plants into the larger 75mm wrapped cubes.
Your plants are now a stage further, and a good bit larger. Once again, you may wish to choose your best specimens and discard, sell or give away the rest. As before, you have the option of planting these plants into the garden or even into pots of soil. The best way to grow them on is in rockwool of course and here you have the choice using culture slabs or the amazing new greenmix.
GRODAN / TALENT rockwool culture slabs come in a great variety of shapes and sizes to suit commercial growers. The best size for use by the home gardener is the 90 cm (3 ft) or the 120 cm (4 ft) which is an ideal size for growing tomatoes, cucumbers or plants of similar size.
Culture slabs are wrapped in plastic to give better performance. This plastic should not be removed.
The cultivation of plants on rockwool slabs is a major commercial horticultural technique. Thousands of acres worldwide are devoted to it and it is obviously impossible to give complete instructions here. For anyone who is seriously interested in this method of growing plants, a recommended book is "Gardening Indoors with Rockwool" by George Van Patten which is available from Esoteric Hydroponics.
Basic Layout of Recirculating Rockwool System Using 1.2m Slabs and Aqua Trays
This system is based on normal commercial practice in production of cucumbers, tomatoes, peppers and certain flower crops such as roses and gerbera. It is designed for mono-cultural cultivation and is not suitable for mixed gardening. This design is for recirculation of nutrients, if you intend to use a total loss system, you will need a larger tank and provision for run-off. Cultural practices will differ with total loss as opposed to recirculation.
This system will suit a larger growing area and is highly recommended with the following provisions.
Although this is a very simple system, there are certain things to bear in mind before embarking on it. In the first place the tank should be as large as practically possible. This is because the conductivity and pH of the solution will be changing all the time and a large tank will minimise the effects of this and reduce the number of times that you will need to check the solution.
For commercial growers it is advisable to retain at least 2 litres of tank volume per plant in the system. The larger the tank, the better. It is also very important to ensure that the nutrient is sufficiently oxygenated. Fortunately this is very easy to achieve because there will be excess pumping capacity that can easily be diverted back to the tank.
Summary of Hydroponic Systems
Within the next 20 years, these simple systems, or greatly improved versions of them, will be the standard ways of growing plants. It will be commonplace to grow food plants and flowers on rooftops and balconies, in deserts, parking lots and quite possibly on Mars!! You are in the forefront of a revolution in domestic horticulture. Have fun and good luck!
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