Key Aspects of Growing in Soilless Substrates

The Advantages

• Enhanced control of water and fertilizer applications
• Optimal moisture in the substrate   
• Optimal nutrient supply
• Significant advantage in disinfecting between growing periods
• Water recycling enables reduced expenses        
• Environmental solution
• Excellent alternative when soil is not suitable for growing crops due to salinity, drainage problems, etc.        

The Limitations

• Low root volume
• Low nutrient storage
• Trace elements - important to control
• Low buffering capacity
• Fast changes in pH
• Salinity control

The Ideal Substrate

Must have the following properties:

• High water capacity and mobility
• High air content
• Light weight
• Stable
• High capacity to supply nutrients
• Non-salinity

To make efficient use of a substrate, it is necessary to be familiar with its physical and chemical properties; and to enable optimal irrigation and fertilization interface applications.

Physical Properties

• Air/water ratio
• Water content
• Air capacity
• Specific gravity
• Volume weight

Chemical Properties

• EC
• pH
• Mineral content
• Exchangeable cation capacity

Substrate Types

Substrates can be divided into two main groups of inorganic and organic types:

Inorganic Substrates

• Some inorganic substrates are inert. They do not decompose, are not chemically active, have low buffer capacity and exchangeable cation content, and contain no organic material that enables micro-biological activity.
• Chemical changes are quick, necessitating intensive irrigation and fertilizer control.
• This group includes rock wool, perlite, Styrofoam and sponge.
• Mineral substrates that react chemically, absorb and release nutrients, have a medium buffer capacity, and are therefore involved in plant nutrition.
• This group includes volcanic ash, pumice and vermiculite.

Organic Substrates

• Composed of organic materials that absorb and release nutrients to plants, have relatively high buffer capacity and exchangeable cation content compared to inert materials
• Chemical changes are slower, requiring less intensive control.
• This group includes coco peat, peat moss, composts and other organic mixtures.

Growing Containers

• Buckets
• Foamed polystyrene containers
• Continuous polypropylene containers
• Gutters
• Grow bags

The system drainage capacity is crucial to ensure the best air/water ratio for a crop. This is applicable to all types of substrates. Therefore, it is essential to utilize maximum height and length of the container type and ensure installation on the most suitable slope.

Selecting a Container

• Allowance for resistance to chemical and steam disinfection processes must be made when used in greenhouses.
• Containers must be made of UV radiation resistant material.
• Most soilless substrates require relatively high and frequent irrigation applications to balance the air-water ratio.
• It is critical to ensure that spacing between drippers is relatively small, and that low flow rates and anti drain properties are maintained.

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