Hydroponic Mediums Explained

Growing Media

There are many types of media available for use in hydroponics. The function of a medium in hydroponics is to provide support for the plant, ensure that water and nutrients are available to the plant's roots by absorbing and retaining moisture, being porous to provide air circulation and drainage and to provide the protection for the roots from temperature changes. Any media used should not contain any of its own nutrients nor affect the pH of the hydroponic solution applied. Different media are suitable for different types of system as well as being appropriate for different plants. Soil is never used. Below is a list of those commonly found in hydroponics and their benefits.

• Expanded Clay Pebbles Generally used in Ebb & Flow and Drip Irrigation Systems. Are very porous and retain both water and air well. Ideally, should be rinsed before use. Available in different sizes but movement within pots can damage roots. Provides good structural support for larger plants, such as cucumbers, tomatoes and peppers.
• Rockwool An inert sterile medium, available in a variety of different sized cubes (small for propagating, larger for use in certain systems), blocks and larger slabs. Has an extremely useful air-to-solution ratio and it enables easy pH control and is generally the preferred media used by commercial growers, particularly in drip-feed systems and Ebb & Flow systems. Provides good structural support for plants.
• Perlite Being lightweight, with excellent capillary action and an easy to control pH, perlite is a favoured growing media amongst hydroponic growers. Needs rinsing and can be problematic in some systems using filters though.
• Vermiculite Generally mixed with Perlite (using a 1:5 or 1:10 ratio) it holds large quantities of nutrient solution though breaks down faster than most media requiring replacing. Can also be mixed with clay pebbles. Retains a high amount of moisture so is good for plants such as lettuces and herbs.
• Coconut fibre With properties similar to rockwool, this biodegradeable media is gaining in popularity in hydroponics. Good water and air retention as well as being resistant to rot. Available as shredded fibres (good for Ebb & Flow and Drip Feed systems) or in cubes (for propagation).
• Sand Coarse sand works better than fine sand, which tends to become clogged with a poor air/solution ratio and also dries out very quickly but is probably the oldest used growing media in hydroponics. Can also be mixed with gravel if you keep a constant eye on pH levels.