Introduction
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:Â 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.
What do I need to start a hydroponic production unit?
| Garden units 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 homemade unit |
Commercial Water is the most important consideration. Quality, quantity and reliability 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 Dedication |
Open and Closed Systems
TYPES OF HYDROPONIC SYSTEMS
There are two main types of hydroponic systems – closed hydroponic systems and open hydroponic systems. Hydroponic systems that do not involve growing media are usually closed systems, while hydroponic systems that involve growing media (container plants), may be closed or open systems.
CLOSED HYDROPONIC SYSTEMS
In this type of system, the same nutrient solution is recirculated and the nutrient concentrations are monitored and adjusted accordingly.
Keeping the nutrient balanced in such a hydroponic system is a challenge and the hydroponic nutrient solution has to be sampled and analysed at least once a week. The nutrient solution
composition has to be adjusted according to the results. If not managed properly, the nutrient solution might get out of balance.
Closed hydroponic systems include both simple hydroponic systems, as well as sophisticated ones. Here is a short brief of some of these methods:
Deep Water Culture (DWC) hydroponic systems – This is the simplest type hydroponic systems. In this type of systems, plants are suspended in an oxygen-enriched nutrient solution.
The Wick hydroponic systems – This is a passive system, in which wicks run from the base of the plant container down to a reservoir and draw the nutrient solution upwards.
Ebb and Flow – This is the most popular hydroponic system due to its low maintenance and low cost. It is widely used for plug production and potted plants. In this type of system the growing bed is flooded with nutrient solution and then it is allowed to drain. The duration and frequency of the flood depends on factors such as the type of growing medium used, size of containers and plants water requirements.
NFT (Nutrient Film Technique) hydroponic systems – This system uses a continuous nutrient solution flow over the roots. This results in a thin film of nutrient solution around the roots, allowing them both aeration and access to nutrients.
OPEN HYDROPONIC SYSTEMS
In open hydroponic systems a fresh nutrient solution is introduced for each irrigation cycle. The nutrient solution is usually delivered to the plants using a drip system. An adequate run-off must be maintained in order to keep nutrient balance in the root zone.
Difference between soil and hydroponic production
| Hydroponics | Field production |
| No soil is required. | Good topsoil is required. Good soil = good drainage, compost, disease-free. |
| Plants are irrigated automatically. No water stress. | Plants need to be irrigated to minimise water stress |
| Nutrients are available at all times Only soluble fertilizers are used. 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 | Soil borne diseases can build up in the soil. |
| Hydroponic production is not organic because artificial nutrients are always used and plants are usually not grown in soil. | It is possible to produce organic vegetables in soil because one can use organic fertilizers such as compost and manure. |
| Hydroponics is usually in a protected structure. Guarded from animals, UV rays, wind and hail. | Open field production can have many risk factors such as animals and harsh weather. |
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.
Greenhouse
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.