Hydroponic growing mediums

Hydroponic growing mediums: What do I use instead of dirt?

hydroponic growing mediums

Hydroponic growing mediums have an essential job. They need to:

  • support the main stem,
  • help the root system get air
  • allow the nutrients to circulate around the roots

Most anything can make a suitable medium.

Net Cups

hydroponic growing cups

Regardless of what you choose for a medium, the medium is often put into a net cup. 

Net cups are little baskets that come in many sizes, and I often use the 2″ size. Remembering that the primary purpose is to hold the stream, a 2″ cup will accommodate most vegetables.


Rockwool for hydroponic growing mediums


Rock Wool is made from heated rock, spun like cotton candy into strands then formed into cubes.  The cube is designed to fit into a net cup.

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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, even if you are not a hydroponic grower.

Seeds can be started in rock wool then planted directly into the ground if you are a traditional soil planter. They are perfectly safe.

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

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

The blocks easily pull apart for single use.

The porous nature allows for airflow around the roots.

Rock wool can quickly 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 overnight bath in water with a couple of tablespoons of lemon juice works well.

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


hydroponic growing medium

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

Straight perlite is excellent for starting plants from cuttings.

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

Plus, it is an excellent addition to other mediums. Most often used with Vermiculite.

Most Hydroponic growers don’t typically use it as a stand-alone hydroponic growing medium since it can easily wash away and clog pumps.

DON’T use perlite with Aquaponics. Any of the particulars in your tank can kill your fish. Perlite, 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.

Vermiculite as hydroponic growing mediums 

vermiculite for hydroponic

Made from crushed minerals, Vermiculite has much the same benefits and problems as perlite.

A big difference is that perlite does not retain much water, while Vermiculite maintains as much as 30 times its water weight! Vermiculite should not be used alone because of the water saturation.  Remember, you can drown your plants.

Vermiculite and perlite work very well together. The mixture works best in a non-circulating system because of the washout factor, and the mixture can get sucked into the pump damaging it.

Coir or Coconut fiber

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

It works well 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 weight in water. It also retains about 22% air when completely saturated.

Because of coir water retention, it is best when mixed with perlite or clay balls to help overall drainage.

The PH runs between 6 to 6.7.

Some studies also suggest that it naturally repels insects.

I love to mix coir with potting soil to help give the soil a lighter feel with good water retention.

Clay Balls hydroponic growing mediums

clay ball for hydroponic

Maybe the most universally used hydroponic growing mediums. Clay balls are made from heated and dried clay, and clay balls have a neutral PH.

They allow maximum oxygen to the roots, don’t have much water retention and dry out quickly. Also, they work great in all systems, and it is good to mix them with a water-retaining medium in Dutch buckets. 

You can also use clay balls alone in flood or NFT systems. 

I use them to hold my Rockwool in place in a seed tray.

They can be expensive but will last years.

Hydroponic growing mediums

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

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

For more about the pros and cons of hydroponics and aquaponics, read here “hydroponics vs aquaponics”

Remember, when you grow indoors, you need the best grow lights on the market.  Visit the Sow Good Naturally store for your light needs

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