Beyond Rockwool: Alternative Substrates for Growing Cannabis Hydroponically


There’s a world of alternative cannabis substrates beyond Rockwool we think you should know. Here are just a few of them. Hydroponics has become the preferred choice for cannabis growers who want to cultivate their cannabis in a controlled environment that doesn’t require substantial water inputs via irrigation. There are many other advantages to growing hydroponically, including having control over nutrient delivery, and in many cases, plants can be harvested sooner than those growing in soil-based substrates. 

Growers have many decisions to make when it comes to growing cannabis hydroponically. One, of course, is what type of hydroponic system is most suitable for growing cannabis. The other is what substrate to use. 

While Rockwool has been a mainstay in hydroponic growing for years, it has drawn criticism because it can’t be recycled by simply tossing it into a compost pile or garden bed. Rockwool is made from rocks and minerals that are not biodegradable. Thus, a lot of it will eventually end up in the landfill. 

The pH of Rockwool is also high. Therefore, nutrients solutions and pH must be closely monitored and adjustments made accordingly, involving more work and expense for the grower. And finally, while further studies may be needed, there are concerns over the safe handling of Rockwool.  

Let’s take a look at some alternative substrates growers are using to grow a great crop of cannabis hydroponically.

Coco Coir

Derived from the waste product of coconut harvests in Sri Lanka and other tropical zones, coconut coir, or coco coir, is gaining in popularity among cannabis growers for several reasons, including: 

  • It’s considered a sustainable product because it comes from the husks of coconuts that would otherwise be discarded. 
  • It can be used in most hydroponic systems for growing cannabis, including ebb and flow and wick and drip systems.  
  • Coco coir is pH neutral, which makes managing nutrients in hydroponic systems a little easier. 
  • It hydrates quickly and has an excellent cation exchange capacity.  
  • Unlike peat-based growing mediums, which decompose in a matter of months, coco coir is a long hauler, taking years to break down. This makes coco coir a good choice for closed-loop systems where it can be reused after sterilization.
  • When coco coir is used in hydroponic growing, fewer nutrients leach from the media into the water. 
  • Coco coir is versatile; it can be used in seedling production, cuttings, and to grow mature cannabis plants.

One criticism often overheard about coco-coir is that it may contain high levels of salt. So it’s crucial to acquire your coco coir from a company like Riococo Worldwide. We cure our coco coir in freshwater and manufacture coco coir in the most sustainable manner possible, including curing the fiber in the sun rather than in dryers that use energy.

Clay Pebbles

Clay pebbles are small clay balls that have been kiln-fired to create pores suitable to use by themselves in hydroponics or added to a potting medium. Clay pebbles are often used in flood and drain and ebb and flow hydroponic growing systems. Seeds can be planted directly into the pebbles, but cannabis growers are more likely to transplant into the pebbles that line the bottom of the growing container. 

Like coco coir, clay pebbles are popular with growers who are looking for an excellent growing medium for hydroponics and one that is biodegradable. Some of the benefits of using clay pebbles include:

  • They’re pH neutral, making it easier to manage nutrient delivery.
  • They provide good aeration to the root zone.
  • Nutrients aren’t released into the water.

The downside to clay pebbles is that salts can accumulate if not managed well, and the substrate can dry out quickly. Thus, the clay pebbles should be flushed regularly with a half-strength nutrient solution or a commercially available flushing agent. In addition, some substrates retain moisture better than clay pebbles. For instance, coco coir and Rockwool can each absorb 5-8 times their weight in water. 

Perlite, Vermiculite, and Other Growing Mediums

There are other substrates that growers can consider, although they’re not as versatile as those mentioned above. 

Perlite is made from volcanic rock and is usually added to peat-based growing mediums. This lightweight compound helps allow oxygen to the growing medium and provides good drainage. Perlite is a good choice for wick-type hydroponic systems. However, it is so light it can only be used for starting seeds and cuttings. 

Vermiculite is also added to peat-based growing mediums but for the opposite reasons as perlite. Vermiculite is added for its ability to retain water. Like perlite, vermiculite isn’t recommended to grow mature plants but rather to start seeds and cuttings. 

Sphagnum peat moss is yet another growing medium used in hydroponic systems. The long strands of absorbent material retain water well and offer good aeration. Although it is a readily available product, it is often passed up by hydroponic growers because it decomposes relatively quickly, which can clog pumps and drip emitters. 

Coco Coir – A Better, More Sustainable Option for Superior Cannabis Cultivation

Growers must decide which hydroponic substrate works best for them based on price, availability, and the pros and cons of each product. Coco coir is one alternative to Rockwool that is becoming increasingly popular in the cannabis industry because it can be used in all stages of cannabis production. Riococo Worldwide manufactures a coco coir product that is sustainably harvested and is cured in freshwater, thus avoiding issues with salt contamination.  

Like coco coir, clay pebbles are readily available to growers and are biodegradable; however, they’re not as likely to be used for seeding or cuttings. Likewise, perlite, vermiculite, and sphagnum peat moss each have their limitations regarding growing cannabis. Are you ready to take your cannabis cultivation to the next level – sustainably? We can help.