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 Hydro pot, 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. Hydro pot 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 capsicums and most popular flowering plants there is a huge choice of suitable containers available at local garden centers. 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, straw-berries or virtually any small plants.

Growing Media

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.  

Perlite

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 tendency 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 liter sacks from Esoteric Hydroponics.

Green Mix

Green Mix 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. Green Mix is now available from grow shops everywhere. Please ask your dealer for more information. Green Mix 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.  

Simple Steps to Successful Pot Culture

We will assume that you already have plants ready to be planted out. Once you have your small seedlings or cuttings, you will be ready to move into pot culture.

Pot Culture - with Perlite

The first step is to reduce the size of the holes at the bottom of the pot. Large holes will allow perlite to wash out but they can easily be reduced with a simple strip of waterproof tape such as ducting tape which is available from any hardware store. Small holes must of course be left on the bottom of the pot to allow the free passage of nutrient solution into the pot and upwards into the root zone.

The perlite can now be added to the pot and it should be filled to about the ¾ mark. Moisten the medium thoroughly with a hose or watering can. Once wetted, there will be no further problems with dust from perlite (see warning below). Make a suitable hole in the center of the pot and place your seedling or cutting in it. Add more media as required and rake it around the plant then firm it down as you would with soil.

Water your new plant thoroughly with half strength Optimum, ensuring that reservoir (saucer) is full. With perlite you should always water from the top through the medium until the saucer is full. You will need to make sure the saucer is topped up at regular intervals. While your plants are small they will probably only require watering every three days or so but they will grow very quickly and before long you will be needing to water them every day. You should try to let the saucer get empty but not dry between watering as this allows good aeration of roots.

Never let the saucer dry out completely. It is advisable to flush your pots by water with plain tap water until it runs out at the bottom of the pot, about every 4 weeks to remove any potential build up of salts. 

WARNING! Dry perlite is very dusty and is best handled outdoors. Care should be taken to ensure that dust is not inhaled as it may constitute a health hazard. Green Mix can easily irritate the skin and is best handled with plastic gloves.

Maintenance of Plants in Pot Culture

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.

Clay Pebbles	Green Mix
Vermiculite	Perlite

Pot Culture - Green Mix

Green mix is a blend of mineral fibers 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 green mix 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 green mix as follows.

Half fill a suitable plastic pot with Green mix. Pot sizes as with perlite culture above. Water gently with half strength liquid nutrient solution until well wetted throughout. Remove plastic sleeve from the wrapped cube and gently place it in the pot. Add more green mix around the plant until it is well supported on all sides. Ensure that the wrapped cube is covered. Water gently with more liquid nutrient solution until it is running out of the bottom of the pot.

Place the pot in a tray or saucer. Ensure that there is nutrient solution in this tray at all times. As long as there is some moisture in the saucer, you can be sure the plant is supplied. Due to the fantastic capillarity of Green mix, it may be found best to add nutrient to the saucer rather than through the pot. You will find that it will soak up large amounts of solution. Ensure that you leave the tray or saucer full after each watering. Allow it to get almost empty before watering again. 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 sterilizing 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 sterilize them with bleach between crops but remember to rinse them thoroughly. Green mix is difficult to reuse and is probably best used as a valuable addition to potting soils or just dug into the garden beds.

Smaller Plants

Discarded lengths of PVC pipe are ideal for suspended planting of strawberries or herbs. Storm water 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 hole saw 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.

Active Systems

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.

Question: Should I re-circulate my nutrient or should I build a "total loss" system?

Answer: This decision is basic to your choice of a new system and you have to decide this before you go any further. A re-circulating system is based on a tank of nutrient which circulates through the system and back to the tank on a regular basis. A total loss system will supply nutrients to the plant on a regular basis and then the excess will run to waste. For smaller growers, this choice is easy as a total loss system is much harder to build and manage on a small scale than a re-circulating one. Total loss is best suited to the larger greenhouse and is very difficult to operate indoors. For the purpose of this fact sheet, we will be concentrating on re-circulating systems as these are best suited to most hobby growers.

Flood and Drain (Ebb and Flow)

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 liters = weight in kilos (1 liter 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 fact sheet, 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 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 minimize 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 liters of tank volume per plant in the system. For smaller operations, however that ratio should be increased to at least 3-5 liters per plant. 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.

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.

When adjustments are made to pH or Conductivity, it will be possible to close valve B completely, shutting off supply to the plants, while opening valve A to the fullest extent. This will increase the agitation in the tank and make a very quick job of
the adjustments. NB, it is very important that there is not more solution in the system than the tank can hold otherwise a power cut could cause a flood.

Nutrient should be supplied to the gullies at between 1 and 2 liters per minute, depending upon the gully width. This is easy to measure with a plastic drink bottle or similar which can be held under the supply tube to one gully while you measure the time it takes to fill. This will be adjusted by opening or closing valve A, remembering to keep valve B wide open. You should now run your NFT system for a day or two to make sure that there are no leaks before placing plants in it. Larger plants such as tomatoes are best propagated in the Rockwool wrapped cube and should be placed into NFT gully as soon as roots begin to appear at the bottom of the cube (not before). Smaller plants, such as lettuce, herbs and strawberries can be placed bare rooted into the nutrient film. 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:

1. Correctly formulated for NFT NFT is the most demanding form of hydroponics as far as the nutrient solution is concerned.
As there is no medium to act as a buffer, the solution must be in good balance with all the elements required for good plant growth. It is advisable to insist on a twin pack liquid formulation such as Optimum or Power Grow which is formulated specifically for NFT systems. Ensure that the solution you choose has fully chelated trace elements which is of great importance in NFT.

2. Correct pH and Conductivity Once again, these things are much more important in NFT than in passive systems. PH should be maintained at 6 and needs checking and correcting on a daily basis. Conductivity requirements may vary during the life of the crop. A good starting point would be around 2 milliSiemens which is normal full strength for products like Optimum or Power Gro. It may be advisable to increase this with plants such as tomatoes when they are setting fruit.

3. Aeration and temperature Nutrient solution should be constantly agitated to ensure maximum aeration and heated with
an aquarium heater to maintain temperature around 18-22°C.

Rockwool Systems

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.

Soak wrapped cubes in a weak and slightly acidic nutrient solution such as Formulex. Ensure that cubes are thoroughly wetted. Gently remove small cubes from SBS tray and insert them into the holes in the top of the wrapped cubes. Remember to label all your plants clearly. Place your plants in a warm sunny place to grow on. Check them for moisture daily. Give them a sprinkle of nutrient solution as needed. Check the underside of the large cubes regularly. As soon as new roots begin to emerge it is time to think about planting them on once more.

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 green mix.

Rockwool Cubes

Culture Slabs

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.

Lay your culture slab on a clean surface. This should preferably be its final location as it will not be easy to move once it is planted up. Attention must be paid to drainage. This can be achieved by placing the slab on a board with a slight slope from end to end. Nutrient will drain from the lower end of the slab and can either be collected or allowed to run to waste.

The easiest way to handle slabs is by using the Aqua tray which holds the slab firmly and has built in drainage holes. Place culture slab into the aqua tray. Mark positions on top of the slab where you intend to place the plants. After placing a wrapped cube in the chosen place, draw around it with a felt pen. Then make two diagonal cuts wit a sharp knife forming an X inside the square. Do this with all plant locations on the slab.

Make up at least 10 liters of nutrient solution. Pour the solution slowly into one of the openings on top of the slab. Keep pouring slowly until the slab is full. The sides will bulge out at this point and it will be obvious that the slab is completely full. Allow to stand for at least an hour, preferably overnight. Before planting, just lift the lower end of the slab out of the tray and make a couple of short cuts in the plastic sheet with a sharp knife. This will allow the nutrient to drain out through the lower end of the aqua tray. Fold back the cut pieces of plastic and place your wrapped cubes on top of the culture slab.

Do not remove plastic sleeve from wrapped cube. Make sure that the Rockwool surfaces come into contact and are not separated by plastic. Now place your aqua tray in a warm sunny place or underneath a good quality horticultural light. The best way to supply nutrient solution to the slab by drippers which should be activated at least twice a day and should run until surplus nutrient is flowing out from the slab. Alternatively, you can water daily with a watering can. Once again, make sure that watering continues until an excess runs out from the bottom of the slab.

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.