Hydroponic growing mediums: what works and why

Clay ball, cocnut fiber, coir, duckygrows, dutch bucket, Greenhouse, greens, grow medium, Hydroponic, hydroponic method, indoor garden, introduction to hydroponics, Kratky, NFS, NFT, perlite, rock wool, urban farming, Urban garden, vermiculite -

Hydroponic growing mediums: what works and why

Hydroponic growing mediums have; support the main stem, helps or does not hinder the root system from getting water, nutrients and air.

Most anything that does that can make a good medium.  The most traditional and often used in Hydroponics are:

Rock wool


Rock Wool is made from rock that is heated, spun ....like cotton candy...into strands then formed into cubes

Used in a net cup to support the plant in most systems.  Not useful in flood systems since the rockwool tends to retain too much water

It is easy to use for starting seeds.  When the tap root grows thru the bottom of the cube the seedling is ready to go into a system.

 It can be pulled apart and reformed to support cuttings or seedlings started in other ways.

Some rockwool comes individually wrapped to keep light from the roots.

The porous nature allows for air flow.  

Rock wool can easily get over saturated.  So keep out of direct water or a wicking system.

It can be cleaned and reused several times but be careful not to squeeze it.  The air pockets that are so beneficial can be damaged

It can be high PH so Rock wool needs to be presoaked in PH low water before use

NOTE:  rockwool insulation is not the same as and is not a good substitute for agriculture rockwool 



Perlite is made from volcanic glass.  Gardeners have been using it for years to help aerated soil.  It’s the white stuff you can see in most bags of premixed soil.

Straight perlite is great for starting plants from cuttings.

It is very porous and PH neutral.  It is reusable.

Must Hydroponic growers don’t use it as a stand alone medium.  It can easily wash away and can clog pumps.

It is a great addition to other mediums.  Most often used with vermiculite.

DON’T use perlite with Aquaponics.  Any of the particulars in your tank can kill your fish.  Parlite, which are small pieces of volcanic glass, will get into the gills when the fish breathe 

Perlite also can cause a danger to people.  So always wear a breathing mask and protective clothing 



Made from crushed mineral, vermiculite has much the same benefits and problems as perlite.

A big difference is that perlite does not retain much water and can be used along.  Vermiculite retains as much as 30 times it weight of water! Vermiculite should not be used alone because of the water saturation.

Vermiculite and perlite work very well together.  The mixture works best in a non circulating system because the washout factor 


Coir or Cocnut fiber


 Coir is made from the waste remains in the coconut industry.  Cocnut fiber is just Cocnut husks ground up. It is all natural and a good use of what otherwise would be waste. Seen often as a base for hanging baskets

It works will in any non flood Hydroponic system.

Coir will hold up to 8x its wieght in water.  It also retains about 22% air when completely saturated.

Because of its water retantion it is best when mixed with perlite or clay balls to help overall drainage

The PH runs between 6 to 6.7.

There are studies that also suggest that it naturally repells insect.

It can come lose and clog pumps 


Clay Balls


Maybe the most universally used medium.  Clay balls are made from heated and dried clay.

Clay balls have a neutral PH.

They allow for maximum oxygen to the roots. They don’t have much water retention and can dry out quickly  

Clay Balls are completely reusable. 

You can use clay balls alone in flood or NFT systems.  They are also great when mixed with a water retaining material like coir for use in any hydroponic system

They can be expensive but will last years.

That is some basic information to get you started.  Most hydroponic gardener find some combination that works best for them.  

Experiment and have fun. Just remember the basics; support, water and air

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