Hydroponic Growing Mediums

by Simon on July 25, 2012

A good hydroponic growing medium is one that:

1. Should be able to stay pH neutral over change and buffer pH changes.
2. Hold nearly equal concentrations of air and water
3. Able to hydrate and re-hydrate quickly
4. Can be recycled/reused and is biodegradable
5. Cheap and easy to obtain
6. Lightweight and easy to move around both outdoors and indoors

The best hydroponic medium also depends on the type of hydroponic system you will use. The most commonly used mediums for hydroponics are: Coconut Coir, Agricultural Grade Perlite, Expanded Clay Pellets, Rockwool and Common Pea Gravel.

Other less common growing mediums include Composted bark, gravel, oasis, peat moss, pumice, sand, saw dust, soiless mix(s), Vermiculite and gravel.

You can mix mediums together. For example Coco Coir is often mixed with 50/50 perlite to provide a higher air holding ratio than Coconut Coir alone. Also a good combination is

Coconut Coir

My Favorite growing medium is coconut coir otherwise known as coconut fiber. Coconut coir combines the air retention of perlite, with the water retention of vermiculite and it is a completely organic medium. It can be reused and is biodegradable, relatively cheap and easy to obtain. It is also lightweight and easy to work with. Another benefit of using Coconut coir as a growing medium it offers plants protection against fungus and root diseases due to its anti-fungal properties. For all of these reasons coconut coir is becoming one of the most popular growing mediums amongst hydroponic gardeners.


The advantage of Perlite is that it has excellent oxygen retention and is very lightweight making it easy to transport. It mixes well with other growing mediums. For example it can be mixed with soil and soil free mixes to provide greater oxygenation for the plant roots.

While its lightweight properties make it easy to transport and work with a disadvantage is that it can get washed away in some hydroponic systems, for example the Ebb and Flow system. However it works well with the wick type hydroponic systems as perlite has good wicking action.

Expanded Clay Pellets

LECA stands for Lightweight Expanded Clay Aggregate and is very loose with large grains. The advantage of expanded clay pellets is that they remain pH neutral and are reusable. This makes them cheaper and environmentally friendly. The advantage of clay pellets is the shape and internal structure of the pebbles which ensures good root aeration and drainage and helps prevent rotting.

The disadvantage is that expanded clay pellets are dusty, so they will need to be rinsed thoroughly before going into your hydroponic system.


Rockwool is made from molten rock that has been spun into long, glass-like fibers. Rockwell is usually sold as cubs or in a loose form. Rockwool is used in wall insulation and is popular amongst the commercial greenhouse industry. The advantage of Rockwool is that it can be used for a wide variety of hydroponic systems, it easily absorbs water and drains well. It’s also completely sterile and non-toxic and makes for a good starting medium for seeds, cuttings and small immature plants. If your system constantly recirculates your nutrient solution, a fast draining medium such as Rockwool is ideal.

The disadvantage of Rockwool is that because it is not natural, it is not biodegradable. Gardeners have complained of the substance irritating their skin.

Common Pea Gravel

Pea gravel is made up of stones less than an inch in size. Like expanded Clay pellets they remain pH neutral and are reusable. Unlike expanded clay pellets they are heavier which can make transportation more difficult.

The advantage of using a heavy grow medium is that the medium does not get washed away with Ebb and Flow type systems.


Why is Ventilation Necessary?

To maintain adequate grow room ventilation, grow room fans can be used to control humidity, temperature and carbon dioxide levels. A grow room fan or hydro fan within a grow room is essential for a number of reasons. By exchanging, circulating and mixing air, a hydro fan will give you more control over the following:

sciarid flyInadequate ventilation can lead to high humidity and this can result in a number of problems for the plant at various stages of growth. A humidity of 60% RH (Relative humidity) is recommended during vegetative growth and around 40% RH during flowering to prevent flowers or fruits from rotting. It will also help to prevent fungal diseases as fungal spores thrive in humid, stagnant air. Stale stagnant air also provides other airborne pests such as sciarid flies a greater opportunity to infest your grow room. Hot air holds more water vapor so by extracting hot and humid air and replacing it with cooler less humid air, high humidity will become less of an issue.

Carbon Dioxide
Plants need carbon dioxide or CO2 to grow and photosynthesize – this is essential for plant growth. Plants within any confined space will soon use up that carbon dioxide. A hydroponic extraction fan is therefore necessary to maintain high levels of carbon dioxide and ensure a fresh supply of air into the grow room. It is recommended that you should try to replace the air in your grow room at least 20 times per hour or every 3 minutes to maintain a reasonable air quality.

Hydroponic lights within a grow room can produce a lot of heat. When the lights are on the temperature should range between 21 to 28 degrees centigrade (70 to 82 Fahrenheit). Try and reduce this temperature by about 5 degrees Celsius (9 degrees Fahrenheit) at night as this is important for correct flower maturation. Grow room ventilation using a hydro fan will help maintain the correct temperature. A hydroponic fan speed controller will enable greater control of the temperature as they can be controlled by a thermostat. A fan speed controller linked to a thermostat will enable you to vary the speed of the hydro fan automatically depending on your preferred air temperature.


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