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Hydroponic growing mediums

Hydroponic growing mediums What do I use instead of dirt?

Hydroponic growing medium Strawberries in clay balls

Hydroponic growing mediums have an important job. They need to support the main stem, help or at least not hinder the root system from getting water, nutrients and air.

Most anything can make a good medium.

Net Cups

Regardless of what you choose for a medium most often a cup is also used. Net cups are little baskets that hold your medium. They come is lots of sizes. I most often use the 2″size. Remembering that the main purpose is to hold the stream, a 2″ cup will accommodate most vegetables.

Hydroponic growing mediumsNet cups

Let’s look at the best thing to use in the cups.

The most traditional and often used hydroponic mediums are:

Rock wool hydroponic growing mediums

 Hydroponic growing mediums

Insulation vs plants

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.  Don’t use rock wool in flood systems because the rockwool tends to retain too much water.

It is easy to use for starting seeds too.

If you are soil planting seeds can be started in rock wool then planted directly into the ground. They are perfectly safe.

When the tap root grows thru the bottom of the cube the seedling is ready to go into a system.

Hydroponic growing mediumsRockwool

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

The blocks easily pull apart for single use.

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. An over night bath in water with a couple of table spoons of lemon juice works well.

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 and is reusable.

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

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

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 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. The mixture can get sucked into the pump damaging it.

Coir or Coconut fiber


Coir is made from the waste remains in the coconut industry.  Coconut fiber is made from ground coconut husks. It is all natural and a good use of what otherwise would be waste. Seen often as a base for hanging baskets. However most hydroponics use fiber that is more finely ground.

It works will in any non flood Hydroponic system. In flood systems the fibers can be washed out of the net cups and clog the pump.

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.

Clay Balls hydroponic growing mediums


Maybe the most universally used hydroponic growing mediums.  Clay balls are made from heated and dried clay.

Clay balls have a neutral PH.

They allow for maximum oxygen to the roots and don’t have much water retention and can dry out quickly. Also they work great in all systems. It is good to mix them with a water retaining medium in Dutch buckets. You can use clay balls alone in flood or NFT systems. They are great for holding rock wool in a seed tray. The uses are endless.

Clay Balls are completely reusable.  To find out how to sterilize the clay ball for safe reuse read “how to sterilize clay balls”

They can be expensive but will last years.

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Hydroponic growing mediums

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

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

Please visit YouTube Momsindoorgarden for more information.

As always questions and comments are appreciated


Please check out Sow Good Naturally Esty store for great grow light options

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