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Best Hydroponic Substrates For Cannabis Plants

Added 6 July 2022

several pots in growing medium

Many growers appreciate hydroponics. 

Whether it’s due to higher yields or they don’t want to grow cannabis the conventional way with soil, they have various reasons to choose hydroponics. 

You get to exercise utmost control with a hydroponic system. It’s a terrific way of growing cannabis, where you use water and nutrient solutions to feed the plants. 

But among the variety of hydroponic setups, you are likely to run into one common question — which is the best growing medium for your setup?

Know the answer in this article.

Why Do You Need a Growing Medium for Your Hydroponic Setup?

growing medium

Hydroponics has been used to grow plants since 3000 BC, but since then, the premise has been the same. You use nutrient solutions to feed your plant, not soil. 

Soil is the classic growing medium, but it contains a rich ecosystem with constantly varying nutrient quantities, pH, and microorganisms, which make it less reliable for growing cannabis.

This is where hydroponic systems come in to offer an alternative — you can use an alternate substrate to grow your plants. Here, the substrate won’t nourish your plant but offer an anchoring point for the roots. 

While some hydroponic setups do just fine without a growing medium, like aeroponics or ebb and flow, you can’t deny the excellent advantages that an alternate growing medium can offer you. Here are a few benefits:

  • Hydroponic mediums are devoid of any nutrients, so you can fine-tune your plant’s nutrient cycle, so your plants can grow with more vigor
  • Since you feed the plant with water and nutrient solution, the roots are constantly hydrated and aerated, leading to better root growth and health
  • Hydroponic mediums’ primary task is to help the roots stay put by imitating the soil but without the latter’s disadvantages
  • Hydroponic substrates are also easy to maintain and do not catch soil-based diseases or develop pests

The benefits of using a soil-less substrate in your hydroponic system are unmatched, which is why you should use them for growing cannabis.

What to Look for in a Hydroponic Growing Medium?

aerated growing medium

Not all hydroponic growing mediums are the same — the quality may vary among the same substrate and some mediums are not as good as the others. So, when choosing a medium for your setup, look for the following features:

  • Air and Water Retention Capabilities 

The medium must be able to retain air and moisture so the roots have enough time to breathe and absorb all the nutrients. However, if the retention capabilities are too high, it can even drown the roots. 

So, the medium must also be porous enough with good drainage to strike the right balance.

  • Right pH Levels

pH is essential for good nutrient absorption, and it should be slightly acidic, ranging from 5.5 to 6.5. So, the substrate’s pH must be around this range. Otherwise, it can alter the nutrient solution’s pH, causing various nutrient-related problems in the plant.

  • Consistent Particle Size

High-quality mediums would also have a consistent size, which is crucial for your hydroponic system’s smooth functioning. Irregular sizes can cause clogs in the system.

  • Pathogen Free

Lastly, the growing medium must be free of pathogens and pests, so that it does not pose a risk to the plant and its roots.

What are the Best Hydroponic Growing Mediums?

You know why you need hydroponic mediums and what to look for, so let’s narrow down the equation with the best hydroponic growing mediums. You can choose the one that fits your preferences and growing setup.

Here are the best hydroponic growing mediums you can choose from.

  • Clay Pellets


One of the most popular growing mediums for hydroponic cannabis is hydroton, also known as expanded clay pellets or lightweight expanded clay aggregate (LECA). These are small balls of clay made by expanding and heating clay.

Clay pellets are ideal for most hydroponic setups, especially ones with deep water culture (DWC) because they are porous, lightweight, yet sturdy enough to support the plant. This is the same reason you would find clay pellets mixed in soil for regular setups, too. 

Thanks to their porous nature, they offer terrific aeration for the roots, however, they are not the best when it comes to water retention. However, they offer a healthy environment for microbial populations that aid root development. 

They cause fewer blockages in the setups while being easy to reuse after sanitization. Plus, they are straightforward to use for new growers.

But, they do have a few downsides. They can cause plumbing problems and are somewhat expensive to purchase in some regions. 

They also must be sterilized before transplanting to remove the white powdery substances that may otherwise affect the roots’ health. So, if you are planning to purchase clay pellets, it is recommended to pay the higher price and get the ones that are prewashed and pH adjusted. 

  • Rockwool Cubes


Think of Rockwool cubes as cotton candy made of rock — the rock is heated at extreme temperatures, molten, and spun at high speeds to create Rockwool cubes. Thanks to this process, Rockwool cubes get a porous structure with amazing aeration and water retention capabilities. 

Using Rockwool requires some experience because you have to be a bit careful while transplanting the seedlings, and there is a lot of unreliable information about it on the internet. You need to research well, but it is worth the effort. 

You also have to prepare Rockwool before placing the seedling. Immerse the Rockwool cubes in your nutrient solution with an electrical conductivity (EC) of 0.5 to 0.6 and a pH of around 4.5 to calibrate the cubes’ pH levels. Submerge for a day at least, or more, if required. 

  • Coco Coir

coco coir

You often hear about coco coir in the Asian growing communities. Coco is another terrific growing medium. It is made of ground-up coconut husks and works a lot like regular gardening soil.

Plus, since it is made of coconut waste and is biodegradable, it is also one of the most eco-friendly growing mediums in the market. 

The benefit coco coir has over the soil is that it is renewable (can be reused for five years) and has better water retention capabilities. Its aeration is also good, along with a neutral pH. Most importantly, it is fungi-resistant, offering more protection to the roots. 

Perhaps one of the best advantages of coco coir is for new growers — this medium is quite forgiving to feeding mistakes, so a small mistake won’t throw off your plant’s growth!

On the other hand, coco coir requires nutrients from day 1 and you need to regularly monitor the pH levels.

  • Perlite


Perlite is an interesting growing medium since it is made from volcanic rock. Here, obsidian (a type of volcanic rock) is mined, crushed, and heated under extreme temperatures. When heated, all the moisture leaves the rock and it expands quickly, turning into light pop-corn-like pellets. 

Perlite is cheap to buy at most gardening stores and is fairly straightforward to use. It's one of the most popular substrates thanks to its aeration and water retention capabilities. It also does not interfere with the nutrient solution, since it is mostly inert with a neutral pH. 

Another benefit of perlite is that it does not degrade over time. If maintained properly, it can be reused for years to come. And it can be quickly washed to bring its pH back to neutral.

The downside of perlite is that since it takes on the pH of the solution, you need to constantly monitor it. Plus, it needs higher watering cycles compared to other mediums because it tends to drain easily. 

  • Mapito


Image Credit - Slimsplace

Mapito is famous among Dutch growers. It is a mixture of coco coir and Rockwool, bringing the best of both worlds together with even better aeration and moisture retention capabilities than Rockwool or coco coir.

Mapito is available in the form of flakes, which adds a few advantages, such as the following:

  • Better oxygenation in the root zone
  • You can move your plants easily
  • Or check the roots’ health by simply picking the plant up
  • Faster water absorption

The downside of Mapito is that you need to treat it before transplanting the seedling, just like Rockwool. And you can’t press it too hard since it can crumble and stress out the roots.

  • Hemp Fiber

hemp fiber

Who knew you could grow cannabis in cannabis? Hemp fiber is just the fiber content taken from special cannabis strains. And it is the most eco-friendly medium out there since it does not contain chemicals or heavy metals. 

Hemp fiber allows your plants to grow quickly while requiring minimal maintenance, and it can hold up well in floods. Plus, it does not require any kind of preparation or sterilization before reusing it. 

However, finding hemp fiber in your region may be difficult due to the strict laws revolving around cannabis cultivation. And touching it with bare hands can irritate the skin, but otherwise, it is safe for humans, animals, and plants.

Summary: Best Hydroponic Substrates For Cannabis Plants

When it comes to choosing the right medium for your hydroponic cannabis, there is no right or wrong. It depends on various factors, like your budget, skill set, preferences, and hydroponic setup. 

Depending on these factors, you can use any of the above-mentioned mediums and your plant will grow bigger than ever. Just remember to choose high-quality mediums and always pH-test them to be sure. Sometimes, the pH may be off in some mediums.




sphagnum peat moss is a hydroponic medium, too. it has no nutrients. it doesn't grow near an ocean (ie not riddled with Na). it doesn't have a messed up ratio of K+ / Na+ / ??? in bonding sites that will derail a grow if the manufacturer doesn't process it correctly.

as with coco you don't want it raw, but the processing is much simple and doesn't invovle removing a sickly amount of potassium for plants.. coco does come with "nutes" and it's incredibly out-of-whack for plants. if someone thinks it's better for the environemnt, you are off your rocker... the amuont of fresh water wasted is hilariously high per volume of coco. gotta soak it in a buffering solution of likely cal-nitrate multiple times, which then is release and causes algea blooms and such... it's not "clean" or "green".

ppl always say, "my coco is fine." It can and will happen, eventually. i've used coco too and liked it. i will use it again (and currently am), but i know it's a potential weak link at any moment. i hated the 'bricks.' never buy the 5kg bricks unless you know what you are doing as far as running a shit load of water through it and thoroughly buffering the material so it doesn't wreak havoc on your resulting nutient ratios in substrate

on top of all that, research done by dr bugbee says sphagnum peat moss is better than these other options. this sort of research is 10x more useful than anecdotal experiences and 20x on sunday. a real effort to compare apples to apples and a suitable sample size to draw such a conclusion or they wouldn't say such a thing... unlike marketing/sales rhetoric that has no integrity whatsoever or ppl's boundless hubris about what they do, personally, being teh absolute best or else their ego might spontaneously combust.

*don't believe he tested rockwool? it's a long video. it's on youtube. believe it's in the "maximizing cannabis yields" vid.

not a fan of clay pebbles/leca balls.. i don't believe it promotes as good of root growth.. maybe not enough fine hairs? or, i'd wager they take up too much volume that the root would otherwise be able to use.

i wasn't a fan of huge, chunky perlite either. #4 and higher? i only use these or the super chunky perlite at the bottom of a pot for water to drip out easily and improve oxygenation at bottom. leca balls are heavy AF, by comparison to other options, too. lugging around a couple 50L bags isn't fun.