Call: 602.753.3469

PureGreens-Logo in white


Picking the Best Growing Medium for Your Hydroponic System

Basil growing in rockwool

The benefits of cultivating crops hydroponically are extensive, and many of them are due to the use of a growing medium instead of soil.

Soil comes with a set of risks for farmers, ranging from soil-borne diseases to invading weeds.

Using growing media instead of soil mitigates these risks.

In this article, you’ll learn how to choose the right medium for you.

Growing media are used in hydroponic systems rather than soil. But growing media aren’t a true substitute for soil.

The media are used to support the roots and stems of plants, like soil, but don’t have any of the nutrients that plants need to grow.

As a result, a growing medium can’t grow a plant on its own.

Growing media are typically porous in order to hold oxygen and nutrient-rich water.

While growing media is similar to soil, nutrient solution is its true substitute.

Nutrient solution is water mixed with nutrients to promote healthy growth.

When choosing a medium, you’ll want to keep three acronyms in mind: WHC, AFP, and CEC.

WHC stands for Water Holding Capacity, which indicates how well the media holds water.

Knowing the WHC of your growing medium is important because some hydroponic systems will be more compatible with lower WHCs and others will be more compatible with higher ones.

For example, wick systems benefit from high WHC mediums, like coconut fiber, because it keeps nutrients easily accessible without overwatering.

Conversely, nutrient film technique (NFT) systems benefit from lower WHC mediums, like clay pebbles, because the plant roots are constantly exposed to nutrient solution. As a result, they use a medium for support reasons more than saturation.

AFP means Air Filled Porosity and refers to the air flow of the medium.

A low AFP means the medium can’t provide the plants with oxygen very well, putting them at risk for drowning and rotting.

Finally, CEC, or Cation Exchange Capacity, refers to how many minerals are in the medium.

In hydroponic systems, a low CEC allows you to have better control over the nutrients your plants receive.

Growing mediums with a higher CEC, like coconut fiber, may require specially tailored nutrient solution in order to achieve the right balance.

Four of the most popular growing media for hydroponic systems are rockwool, lightweight expanded clay aggregate, coconut fiber and perlite.


Rockwool, also known as stonewool, is a porous material made of spun basalt rock fibers.

This growing medium is extremely popular due to it’s high WHC and low CEC. It absorbs easily and drains well, making it a great choice for ebb and flow systems.

Unfortunately, rockwool is not biodegradable so eco-conscious farmers might hesitate.

Plus, it requires being presoaked in water with a pH of 5 to 5.5 for 24 hours. Otherwise, its naturally high pH will make it inhabitable for plants.

Lightweight Expanded Clay Aggregate

Lightweight Expanded Clay Aggregate, also known as clay pebbles, are round pieces of heat-expanded clay.

Clay pebbles have a low CEC and WHC and a high AFP, making it difficult to over-water and easy to provide oxygen. It’s also reusable!

On the downside, clay pebbles are heavy and may drain too quickly for some systems.

As a result, this medium works best for deep water culture (DWC) systems, which keeps plant roots constantly exposed to water.

Coconut Fiber

Coconut fiber, or coconut coir, is an organic, biodegradable growing medium made from shredding the inner pith of coconut husks.

On the upside, coconut coir is a sustainable choice, as it gives purpose to a coconut product that’s usually thrown away. It also traps oxygen fairly well and feels similar to potting soil.

Coconut fiber is somewhere in the middle when it comes to CEC and AFP, but it has a high WHC. As a result, nutrient solution made specifically to balance out its CEC is recommended and it’s prone to overwatering.

These aspects make it especially suitable for drip systems where water intake is highly controlled.


Perlite is a volcanic rock and can be added to other growing mediums or used on its own.

Fans of perlite like that it’s lightweight and has a very low CEC and high AFP, making it easy to control nutrients.

It also absorbs water fairly easily, but not so well that there’s a high risk of overwatering. Therefore, this growing medium works best for wick systems.

However, perlite floats in water. As a result, it’s unsuitable for plant support in systems that submerge the growing medium, such as ebb and flow.

Now that you know how to choose a growing medium, it’s time to start planting!

Our Pure Greens Container Farms use hydroponic systems inside of repurposed shipping containers for an ideal growing environment.

For more information about how you can start your own hydroponic farm, visit our website or call us at 602-753-3469.

More Research For You

Lets Get Started Today!

Ready to talk to an expert about your next container farm project? Our representitives are ready to talk to you now. Contact us!

Your Container Farm is a Click Away

Click the button below to contact us today
Contact Us

Table of Contents