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What You Should Know About Hydroponics Growing Media

In hydroponics, the growing medium takes the place of the dirt or soil. Not to provide nutrients, but so the roots can support the plant’s weight and hold it upright. Just about any inert material can be used as a growing media. Inert meaning that it can’t or won’t decay or break down quickly, thus providing nutrients to the plants. Hydroponic growing media is simply a soil-less material that is generally porous so it can hold the moisture and oxygen that the root system requires to grow. Non-porous materials can be used as well, but using no growing medium at all watering cycles would need to be more frequent so the roots don’t dry out between waterings.

The growing medium won’t be able to grow anything on its own. If you placed plants in hydroponic growing media and watered it with plain water, the plants would starve from nutrient deficiency. It’s simply there to help support the plant’s weight as well as the moisture and oxygen the roots need. The nutrients the plants need are provided by the nutrient solution and is what the growing media is watered and moistened with.

In fact, the purest form of hydroponics, water culture, grows plants with their roots directly submerged in well oxygenated and the temperature-controlled nutrient solution no soil or any other “stuff” required. Why are we telling you this? Well, surely it begs the question, “If hydroponics is the science of growing plants directly in a nutrient-rich solution what’s the deal with all these bags of stuff taking up space in your local grow store?” Again we’re not referring to soil based potting mixes here we’re pointing at the hydroponic growing media such as Coconut Coir, Perlite, Expanded Clay Ball, Stonewool, Growstones and Soilless Mixes.

The main reason why so many hydroponic growers choose to spend money on hydroponic growing media is because they enjoy the buffer of moisture and nutrients should a pump fail. It also affords their plants some physical stability and also provides some thermal insulation for the roots. Arguably by using growing media, you enjoy a wider margin for error as you grow.

Any growing media out there has dozens of characteristics but in practice, you really just need to know about three: WHC AFP and CEC.

  • WHC (Water-Holding Capacity): how much nutrient solution that can absorb.
  • AFP (Air-Filled Porosity): the amount of air space in the media.
  • CEC (Cation Exchange Capacity): how readily the growing media can hold onto and release positive ions to the roots

So, Water Holding Capacity or WHC is really a measure of how absorbent or restrictive a material is — for example Mother Earth Coconut Coir and Grodan Gro-Wool are two examples of highly absorbent or restrictive growing media they can hold between five and eight times their own weight and water.

Because they hold on to so much nutrient solution they need to be irrigated less often. On the other end of the WHC spectrum are hydrogen expanded clay balls available from Mother Earth in regular and giant size absorb relatively little water and as such require very regulate irrigation even constant dripping they’re virtually impossible to overwater so they’re easy to use and in the middle of the WHC Road are Mother Earth Growstones which absorb moderate amounts of nutrient solution while still affording good drainage.

Air-Filled Porosity is important because of roots like oxygen or air gaps in order to respire effectively. Most Coconut Coir products, for instance, are not screened allowing fibers through and for good reason – these fibers really helped to keep air in the mix remember the smaller the particles in any growing media the more moisture it can hold – perlite is often added to soilless mix is such as Mother Earth Coco Coir and Perlite or Vermi-pro because of its high AFP – it basically helps to increase drainage and air supply in the rhizosphere.

Finally, Cation Exchange Capacity – a low CEC means the medium doesn’t hold onto nutrients easily. Stonewool or Rockwool has a low CEC making it very easy to control what’s available to the plant this is particularly handy toward the end of the cycle when it’s time to flush it with pure water. Coconut coir, on the other hand, has a high CEC within its cellulose and traps cations such as potassium, calcium, magnesium, manganese, copper, zinc and boron. These items are subsequently exchanged for other ions in the solution so, don’t worry, they’re not trapped forever. Special coco coir specific nutrient formulations are available which exploit the unique characteristics of this media. Other stuff to consider: cost, obviously!

Here are some of the most widely used growing media right now.

Mother Earth 714830 Coco Plus Perlite Mix

  • Mother Earth Coco substrate is 100% natural
  • It contains the highest quality mix of coco pith and coco fiber. RHP certified for quality, Mother Earth Coco is pre-buffered and pH adjusted to neutral a 6.3-6.8
  • For an optimal hydroponic media, combine Mother Earth Coco with Mother Earth Hydroton or Perlite for increased production. This is uncharged inert media
  • Mother Earth Coco will promote strong root growth, populate microbial activity, discourage disease and insect outbreak and release nutrients evenly

Mother Earth Coarse Perlite

  • Mother Earth perlite is naturally occurring siliceous rock that when heated to 1600° F expands up to 20 times its original volume
  • This kilning process is very similar to popping popcorn and produces a growing media that is sterile and has a neutral pH of 7.0
  • The exceptional physical properties of this perlite make it tops in the perlite world for adding porosity to soil and soilless mixes
  • This perlite has numerous hydroponic applications as well

Hydroton 10 L Original Fertilizers

  • The original hydroton Brand expanded clay is a unique, lightweight expanded clay aggregate made in Germany
  • This natural clay is mined, formed into pellets, then kiln fired at high temperatures to cause the clay to expand into tough, lightweight balls
  • Clay naturally has balanced capillary action, with an ideal surface structure
  • Hydroton Brand expanded clay is semi-porous and generally does not Float like other products can
  • For Best results, rinse all expanded clay before use. It is reusable as long as it is thoroughly cleaned between uses. 50 Liter bags feature an easy pour spout. Size specification is 8-16 mm

Stonewool Grow Cubes

  • Brand: Grodan
  • MPN (Part No.): RW91003
  • Bag Size: 2 cu.ft.
  • Volume: 2 cu.ft.
  • Type: Grow Cubes/Stonewool

Mother Earth Growstone Chunky Growing Media

Vermicrop Organics VermiPro Soilless Growing Medium Bale

  • VermiPro is a soilless growing medium equipped with extremely high porosity which allows for aggressive feedings
  • Highly experienced gardeners designed the ultimate ratios of triple washed coco coir, the highest grade peat moss, aged softwood bark, perlite and mycorrhizal fungi
  • Professional growers use VermiPro as a standalone hydroponic/soilless medium, or combine their own nutrients and organic matter into VermiPro to create a custom soil blend
  • As a standalone medium, it is recommended for indoor or greenhouse use only. When mixed with water retaining organic matter (such as VermiBlend), it creates an excellent outdoor medium
  • This medium was designed to give the grower all the tools necessary to perform like a pro!


There aren’t one growing media that is better than the rest. Especially with so many different hydroponic system designs possible. However many growers eventually favor one type over others. There are a lot of things to consider when choosing what to use as a growing media. The type of system you’re growing in, and how you design and build that system is the biggest factor.

While there are no one best growing media for all situations, some growing media’s work better than others in different systems. With any hydroponic system, and/or any type of growing media, the goal is still the same. You just need the roots to be moist, not soggy and saturated. If the growing media is saturated and soggy, the roots will suffocate from lack of oxygen. That situation can easily lead to roots dying, and root rot.


Hydroponics: Growing Media 101
Growing Mediums and Hydroponics

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