How To Choose A Hydroponic Growing Medium

By George February 17, 2019

Did you know hydroponic growing systems date back to Babylon’s Hanging Gardens? The Aztecs were using these systems to make weed around the 10th century, and the basic techniques of hydroponics remain the same after thousands of years:  all you need is a reservoir with a nutrient solution and a growing medium to support your plant.

If you are wondering how to choose a cannabis growing medium, we have listed the most popular choices in the article below. Under each one, you will find information about the best practices and uses.

What The Heck Is Hydroponics?

Yeah, hydroponics is a fancy-pants word, but it’s not so tough to understand once you break it down etymologically. First off, we have “hydro,” which (surprise, surprise) refers to “water.” As for “ponics,” it’s derived from the Greek word “ponein,” which roughly means “to labor.” So, hydroponics refers to laboring over plants using water rather than soil.

Instead of giving plants nutrients through the soil, people who practice hydroponics use water, some static material (e.g., peat moss, Rockwool, or clay pebbles), and nutrients to help plants grow. This material is called a “growing medium.” There are many different kinds of hydroponic mediums you could choose from, each one with a different set of properties. 

Keeping It Stable: Popular Hydroponic Growing Mediums

While you don’t need soil to grow with hydroponics, you do need some type of static material to provide stability. Let’s consider the benefits and drawbacks of some of the more popular inert materials used in weed cultivation.


A very popular material used by hydroponics cultivators is called Rockwool. This fibrous material made out of basalt rock was initially designed for home insulation. As hydroponics cultivators experimented with different inert materials, however, they grew to love rockwool because it absorbs moisture, yet it’s also highly breathable.

Keep in mind, sometimes the absorbability of Rockwool could pull away too many nutrients depending on what hydroponic system you’re using. One other thing you need to be careful about with this growing medium is the pH level. Rockwool is by nature highly alkaline. Be sure to adjust this level to neutral before putting it into your hydroponic system.


Another popular material used in hydroponics is a light, white substance known as perlite. Basically, perlite is a form of volcanic glass that has been heated to produce microscopic pockets. These small pockets absorb moisture on the exterior and help with oxygenating the water.

Probably the biggest pro for perlite is that it’s cheap. Also, unlike Rockwool, you won’t have to worry about adjusting the pH of perlite because it’s naturally neutral.

Perlite doesn’t absorb as many nutrients as Rockwool, which makes it a perfect medium for hydroponic systems like ebb & flow. Since perlite doesn’t absorb as much residue, it’s also extremely easy to reuse.

The main drawback of using perlite is that it produces a lot of dust that could potentially damage your lungs. Whenever you work with perlite, do yourself a favor and wear goggles and a breathing mask to reduce the risk of irritation. Ideally, you want your lungs to be in top condition to enjoy all that sweet weed you’ll grow.

Coconut Fiber

It seems like everyone is coco for coconuts nowadays, even hydroponics cultivators. Coconut fibers (or coco coir, as it is commonly known), are made from ground coconut husks, are widely used in hydroponic systems similarly to Rockwool.

Coconut fiber is the preferred method for eco-conscious gardeners because it’s organic and sustainable. Another plus for coconut fiber is that it has special hormones that have been shown to protect roots from various diseases.

A drawback of coconut fiber is that you have to look out for lower-grade products that include impurities like sea salt. Don’t try to cut corners if you’re going to use coconut fibers!

Clay Pebbles

Similar to perlite, clay pebbles are a widespread and economical growing medium in the world of marijuana hydroponics. Just like perlite, clay spheres have to go through an intense heating process to create pores that help with oxygenating the water. Usually, you’ll find clay pebbles sold in either red or brown in a gardening store.

The size of your clay pebbles will have a different effect on your hydroponic system. Unsurprisingly, stones that are larger than average hold more water than smaller ones.

You must clean clay pebbles thoroughly and test their pH before putting them in your hydroponic system.  It takes between one to two days of soaking in water with a pH of about 5 for clay pebbles to reach a neutral pH. For the best results, use clay pebbles in systems like Deep Feed Irrigation or Ebb & Flow.


Vermiculite is made out of compressed silicate material, confused with perlite. They both look similar and are usually right next to each other in the gardening store. There is, however, one significant difference between these two materials.

Here’s the deal: vermiculite retains more water than perlite. For this reason, you should mostly use vermiculite in passive systems. Also, it’s not uncommon for gardeners to mix vermiculite with perlite to “get the best of both worlds.”

Most vermiculite pellets are neutral, but you should double-check before placing them in your system. Many gardeners have pointed out that vermiculite produced in Africa tends to be more alkaline than average.

Oasis Cubes

Although Rockwool is more popular than Oasis cubes, both of these materials have similar characteristics and could be used almost interchangeably. 

Oasis cubes are made out of a special foam called (surprise) Oasis. This styrofoam-like material was specifically designed to maximize air and water absorption while maintaining a neutral pH.

Some gardeners like Oasis cubes better than Rockwool because they don’t get as oversaturated with water as Rockwool. Of course, since Oasis cubes are already neutral, another pro is that you won’t have to worry about changing their pH.

The major drawbacks for Oasis cubes are that they aren’t organic or sustainable. So, if you’re an eco-conscious gardener, you’ll need to look somewhere else.

Lava Rocks

One hydroponic growing medium that doesn’t get a lot of press nowadays is lava rocks. Just like the name sounds, lava rocks are essentially hardened magma, like the one that comes out of volcanoes.

The pros of using lava rocks are that they have a neutral pH, provide essential minerals, and are very absorbent. Hydroponic growers have used lava rock successfully for years, especially in Ebb & Flow systems.

Back in the day, lava rocks were as hot as, well, lava. Alas, those glory days have passed, and lava rocks are now becoming increasingly difficult to find on hydroponics websites. The reason contemporary cultivators shy away from volcanic rocks has to do with their jagged edges. Even if you’re super-careful, it’s very easy to damage a plant’s roots using lava rocks.

If you’re going to use lava rocks, then do serious research on the manufacturer. Many lava rocks on the market today have been treated with harsh chemicals that can alter your marijuana yield.

Finding The Right Growing Medium

Now you should have a better sense of why many weed cultivators choose to use hydroponics. For those just getting interested in using hydroponics, it’s best to start with easy systems like DWC (analyzed in depth on our article here). From there, you can do further research into other methods and materials to perfect your style of weed cultivation. Give hydroponics a try if you’re struggling to get the weed you want from soil.