A good hydroponic growing medium has the following properties:
The best hydroponic medium also depends on the type of hydroponic system you will use. Hydroponics gardeners most commonly use coconut coir, agricultural grade perlite, expanded clay pellets, Rockwool and common pea gravel as a growing medium.
Other less common growing mediums include composted bark, gravel, oasis, peat moss, pumice, sand, sawdust, soilless mix(s), vermiculite and gravel.
You can mix mediums together. For example, gardeners often use coco coir mixed with 50/50 perlite to provide a higher air holding ratio than coconut coir alone.
Many gardeners like coconut coir, otherwise known as coconut fiber, as a growing medium. 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 is that 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, you can mix it with soil and soil-free mixes to provide greater oxygenation for the plant roots.
Its lightweight properties make it easy to transport and apply. However, a disadvantage is that the hydroponic system can wash it away (the Ebb and Flow system, for example).
However, it works well with the wick-type hydroponic systems as perlite has good wicking action.
Lightweight Expanded Clay Aggregate (LECA) is a very loose medium with large grains.
The advantage of expanded clay pellets is that they remain pH-neutral and are reusable. This makes them cheaper and friendly to the environment.
Another 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. You would typically buy Rockwool in the form of cubes or in a loose form.
The building construction industry uses Rockwool in wall insulation and it is popular amongst the commercial greenhouse industry.
The advantage of Rockwool is that you can use it for a wide variety of hydroponic systems since 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 it is not biodegradable. Also, gardeners have complained of the substance irritating their skin.
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. This 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.
To learn more about other aspects of hydroponic gardening, see the following sections of our guide.