What is hydroponics? Translated directly, hydroponics means plants working (growing) in water. The word ‘hydroponics’ is derived from two Greek words: ‘hydro’– meaning water, and ‘ponos’ – meaning labour.
A modern definition of hydroponics: A system where plants are grown in growth media other than natural soil. All the nutrients are dissolved in the irrigation water and are supplied at a regular basis to plants.
In South Africa, hydroponic vegetable production is almost always done under protection.
Advantages of hydroponic vegetable production
- Hydroponically produced vegetables can be of high quality and need little washing.
- Soil preparation and weeding is reduced or eliminated.
- It is possible to produce very high yields of vegetables in a small area because an environment optimal for plant growth is created. All the nutrients and water that the plants need, are available at all times.
- One does not need good soil or a garden to grow vegetables.
- Water is used efficiently.
- Pollution of soil with unused nutrients is greatly reduced.
Disadvantages of hydroponics
- Hydroponic production does need to maintained and can be costly to get setup.
- Daily attention is necessary.
- Specially formulated, soluble nutrients must always be used.
The difference between hydroponic vegetable production and production in soil
- No soil is required with Hydroponics. Good topsoil is required for soil grows. Good soil = good drainage, lots of organic matter, disease-free.
- Hydroponic plants are irrigated automatically so they never suffer from water stress. Plants in soil need to be irrigated to minimise water stress
- Nutrients are available at all times.
- Hydroponic fertilizer formulations contain a balanced nutrient content
- Nutrients must be added to soil. Unless a laboratory analysis is done, too much or too little nutrients can be added.
- Soil borne diseases can be eliminated when growing in hydro. Soil borne diseases can build up in the soil.
What do I need to start a hydroponic production unit?
- Source of clean water
- The right location
- Specially formulated fertilizer
- Time to attend to the system daily
- A little knowledge of plants or gardening
- A commercial or home made unit
- Water is the most important consideration. Quality, quantity and reliablity.
- A market. Know what, where and when to market your crop
- Hydroponics is labour intensive. During peak season, labour must be available for 7 days a week
- Management skills: Production, labour, marketing, infra-structure
- Expertise in crop production, fertilization & irrigation, pests and disease management
- Location: Infra-structure, labour, market, etc
- Financing: The amount needed depends on the size, type of greenhouse, labour cost and your market
Know the basics
To be able to produce vegetables successfully year after year, one needs to be familiar with the basics of hydroponics viz: the plant, growth medium, water & nutrients. By relying on recipes only, one will not be able to identify the cause of a problem and you may not be able to correct them.
How do plants function?
Plants have only three types of organs: Leaves, roots and stems. Know what the organs look like and how they function so that you can deal with their needs.
Growth medium is the substitute for soil in hydroponic systems.
The functions of growth medium are:
- To provide the roots with O2
- Bring the water and dissolved nutrients in contact with roots
- Anchor the plants so that they do not fall over
- Many different materials can be used as long as they provide the roots with O2, water and nutrients.
- In South Africa, gravel is popular in re-circulating systems, sawdust is the most popular for the open bag system / drain to waste system.
Water and nutrients
- All the nutrients plants need are dissolved in water and they are supplied to plants every day. Macro elements (N; P; K; S; Ca) are needed in substantial amounts, whereas plants need very small amounts of micro elements (Fe; Zn; Mn; Mg; Cu; Co, Mg).
- It is necessary to use specially formulated fertilizers. Fertilizers used for hydroponics are more pure than other fertilizers to prevent precipitation and blockages of the system.
- Symptoms of nutrient deficiency are normally seen on leaves.
- Symptoms of nutrient deficiency can easily be mistaken for disease symptoms
There are two different hydroponic systems are used to produce vegetables:
The re-circulating system or drain to waste system.
- In the drain to waste system, plants are grown in containers and nutrient solution is supplied to plants by means of a dripper, for up to 12 times per day. The number of irrigation cycles per day depends on temperature and the growth stage of plants. The crops in the drain to waste system grow tall and need to be trained and pruned so that they grow upwards as a single stem.
- In the drain to waste system, the nutrient solution is re-circulated and the roots of the plants stand in a thin film of nutrient solution all the time. Gravel or sand is used most often as growth medium.
Which crops can be grown in a hydroponic system?
Basically all high value crops. Popular in South Africa are tomatoes, cucumbers and peppers in drain to waste systems and lettuce and herbs in drain to waste systems.
Which crop should I grow?
Depends on the choice of the family and the type of unit.
The most important consideration is the market and the climate. Nobody can make this decision for you. Every situation, every crop and every market has it’s own advantages, disadvantages and requirements.
Which variety do I choose?
There are many vegetable varieties available. Some were developed specifically for commercial hydroponic production in greenhouses. Local seed companies are able to recommend varieties that are widely adapted and easy to grow. For house hold units common garden varieties are recommended.
Seedlings can be purchased at nurseries, or you can produce them yourself.
When buying seedlings, look for young plants, the roots must not be stuck to the walls of the seedling tray and must be white, not brown. Soil and water-borne diseases can be transmitted through seedlings so be sure to transplant only the strongest seedlings. Do not use seedlings that are too old and ‘pot bound’. To produce seedlings, follow instructions on seed packages.
Where do I buy seed?
- Seed is available in small or large packages.
- Small packets are sold at nurseries, co-ops and retail stores and are suitable for garden – and small-scale hydroponic units.
- Large packets, suitable for commercial scale production are available from seed companies.
Taking care of plants
- Different crops are planted at different spacing. Small plants can be planted close to each other. Large plants need more space to grow and must be spaced further apart.
- Water flow must be checked every day and adjusted when necessary.
- If plants turn yellow, it is normally a symptom of nutrient deficiency, too little light or a disease.
- Inspect the leaves every day for disease symptoms and insects. Act immediately if a problem occurs.
- Tall plants need to be trained and pruned to make optimal use of the expensive greenhouse space
HarvestingVegetables are perishable. The shelf life and quality depend on a chain of actions:
- Pick at the right stage without damage to the plant.
- Pick early in the morning or when it is cool.
- Keep picked vegetables out of the sun.
- Handle carefully.
- Store them at the right temperature (depends on crop).
- Use the right packaging (depends on crop and market).
- Transport with care.
- Commercial scale hydroponic vegetable production
- Hydroponics is becoming a very important way to produce vegetables in South Africa because of the production potential, the high quality of the produce and the efficient water usage.
High quality Sorrel
If produced in a climate-controlled greenhouse, the producer can supply vegetables out of season when the price is good.
Commercial scale hydroponics production is capital, labour and management intensive.
Why in a greenhouse?
The purpose of greenhouses is to create an environment more favourable to plant growth than the environment outside.
In South Africa plants are grown in greenhouses to protect plants against the strong UV radiation, to increase the humidity around plants, and to decrease to some extent the extreme minimum and maximum temperatures that can occur in one single day.
Most greenhouses in South Africa are covered with polyethylene sheeting or shade netting.
Greenhouses come in many forms and vary from simple and relatively cheap to very sophisticated and expensive.
In South Africa the following are popular:
- Shade net structures: Flat roof, pitch roof and tunnel type
- Plastic: Tunnels and multi-spans
Greenhouse choice depends on the crop, market and financing available
How do we create a more favourable climate in our greenhouses?
Shade netting offers protection in the following ways:
- Cuts out a certain amount of sunlight, in particular harmful UV rays.
- Protects plants against winds, rain, hail, animals, birds and large insects
- Allows for natural ventilation and air circulation.
- Plastic greenhouses offer protection against normal rain, wind and hail as well as UV rays.
- The humidity is higher inside plastic and glass greenhouses than outside. It is possible to heat or cool or heat the air and soil inside a greenhouse. Plastic sheeting retains heat inside the greenhouse during the day. It can become too hot in plastic houses in summer. On the other hand, if the environment cannot be heated, the minimum temperature can be as low as outside the greenhouse.
Do greenhouses offer protection against pests?
Well constructed greenhouses can keep out large insects and problem animals, that’s all. Pathogen spores and small insects cannot be kept out. If the temperature and humidity are very high and ventilation and circulation is poor, one can expect an increase in the incidence of pests and diseases.
Pests and diseases
The optimal growing conditions for plant growth also provide favourable conditions for the development and spread of diseases and pests. Hydroponic producers are thus faced with the challenge of maintaining conditions optimal for plant growth but not for disease or pest development. This balance is often very difficult to maintain, and systems must be managed carefully.
For a disease-causing organism or pathogen to be able to infect a plant and cause a disease, three conditions have to be optimal:
- The pathogen/insect has to be present in the stage that causes infection.
- The plant must be susceptible to infection.
- The environment must be conducive to allow infection to occur.
- This is known as the disease triangle. Any attempt to control a disease or pest will be aimed at one or more of these corners of the triangle, normally the one perceived to be the weakest or the easiest to eliminate or control.
- It is important for a producer to know what pests or diseases is likely to become a problem. Steps can then be taken to reduce the possibility of the pest or disease entering the greenhouse and gaining a foothold on the plants. Prevention is easier than cure!
Tips to prevent spread of diseases
- The most important tools are knowledge and dedication
- Several cultivation practices can prevent the spread of disease
Use of pesticides
Where do I buy suitable pesticides?
Small scale/house hold hydroponic producers can buy pesticides in small packages available at nurseries and certain retail stores.
Commercial producers can obtain bigger quantities from agrochemical companies.
Which pesticide to use?
Pesticides can be effective only if:
- The pest has been identified correctly. (This can be tricky!).
- The pesticide is applied correctly. This includes mixing, spray technique, time of day, etc.
- Contact an expert such as the Roodeplaat Diagnostic Centre (tel: +27 (0) 12 841-9611) if you are uncertain about the identification of the disease or pest.
- Only registered pesticides may be recommended.
In South Africa all chemicals used for the control of any pest or disease on a plant must be registered for such use under Act 36 of 1947 (the Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act). An amendment to this Act (No R.1716 of 26 July 1991) prohibits the acquisition, disposal, sale or use of an agricultural remedy for a purpose or in a manner other than that specified on the label on the container.
All registered chemicals in South Africa are published in a two-volume guide viz. “A Guide for the Control of Plant Diseases” and ” A Guide for the Control of Plant Pests ” issued by the National Department of Agriculture on a regular basis.
Availability: Resource Centre, Private Bag X144, Pretoria 0001 or Tel: +27 (0) 12 319-7141.
- Study the label carefully and apply the pesticide only as indicated on the label.
- Give attention to the safe use of chemicals and the protection of the person applying them.
- Make sure than pesticides do not occur on harvested products.
- All pesticides are poisonous.
Source of information:
Guide to Hydroponic Vegetable Production. 2001. Ed JG Niederwieser. Published by Agricultural Research Council, Roodeplaat Vegetable and Ornamental Plant Institute. ISBN: 1-86849-196-X
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