Wed, Feb 19, 2020

Reviewing six hydroponic mediums.


It’s no longer new and exciting. In many ways it’s fallen by the wayside to a regenerative culture which often demonizes its practices. But there are still a large group of connoisseurs who prefer their indoor Cannabis grown with hydroponic growing methods. I’ve been growing long enough to remember when hydroponic growing was a new and exciting technique in this country.

Fabled stories flowed through the web forums—before there was Instagram we communed online on these things called message boards—of people pulling pounds and pounds of the frostiest, fatty nuggets of dank using inert mediums or just bare roots in nutrient solution.

In this month’s Grow Tech, we’re going to roll back the clock a bit and dive head first into the range of hydroponic growing methods still available and employed by a decreasing number of indoor gardeners.

I feel compelled to first acknowledge the issues and potentials for adverse environmental impacts associated with using the mineral based nutrient solutions that hydroponic growing techniques utilize. It’s also important to mention that there are in fact ways to significantly minimize these impacts, and lest we forget the primary purpose of hydroponic growing methods: namely creating bountiful harvests in areas with adequate sunlight yet extremely arid environments where water is scarce and precious.

Although in the good old United States we subsidize water, but still hold regulations preventing rain collection and greywater systems. We then turn around and sell partially purified sewage in indestructible plastic containers for 1,500-2,000 percent profit back to consumers. Most of the world does not have unlimited access to shower in potable water. It’s a precious resource and its value has already begun to be revealed in the wake of the natural disasters of recent. So, while the benefits and sustainability of producing harvests using very few gallons per gram may not be valued in our little section of the earth, we are unique in this way from the human population. This is all before mentioning that hydroponic mediums themselves are recyclable and reusable, and in no way contribute to the destruction of some of our planet’s largest carbon sinks by way of mining peat moss bogs that many organic soil companies are responsible for.

I’ll now get off my sustainably mined, free range, vegan soap box and get back to the regularly scheduled geekery.

The six mediums we will be reviewing this month are all strictly speaking, hydroponic mediums. This means that: they are either naked roots with a system designed to deliver a nutrient solution directly to the roots, or they are grown in a medium that is inert. Inert mediums have no or extremely low ability to react chemically and don’t have carry out any pharmacological actions. If broken down, unlike soil, inert mediums do not release any nutrients of any form. As such, most hydroponic growers use bioavailable nutrients that have already been chelated so the plant can take them in right away.

Some folks still insist on swimming upstream and choose inert mediums to cultivate micro herds so they can use organic bottled nutrients in a hydroponic medium, indoors. We are overlooking this group as well as any other using growing techniques so new and contrived by people that they exceed the tried and true techniques that have been employed for centuries.


Utilizing the husks of coconut shells. This medium is often called the crossover medium between hydroponics and organic growing methods. It’s not.  The consistency of the medium is a favorable environment to establish and sustain a population of healthy bacteria and even some fungi which would allow the medium to become effective at breaking down any organic amendments the gardener applies. This is like reaching around your elbow to get to your anus.

What is notable about Coir is that it is collected from a fruit. Combining Coco Coir with mineral based nutrients creates extremely fast growing plants that yield handsomely when optimized like all hydroponic methods. In addition, since coco has the look and feel of soil it also has similar water retention properties. Unlike other hydroponic mediums, coco is unique in that it can hold nutrient solution to sustain the plant without maintenance for longer periods of time than other methods which require submersion or frequent solution application. This makes the medium more forgiving to pump or human failures, temperature and humidity fluctuations, as well as dialing in the perfect nutrient application schedule.


Sourced from glass, these soft fibers are spun into dense blocks or “croutons” of various sizes and even torn up pieces known as mapito. Rockwool is a convenient medium that suits multiple containers, irrigation styles and grow techniques. Due to the intentional design, rockwool can be assembled as part of a system allowing seamless transplant with little or no shock imparted to the plants. Additionally, the widespread use of rockwool has led complimentary companies to innovate and manufacture various inserts, lids and other grow gear specifically designed to be used in concert with rockwool to keep maintenance low and maximize potential of the medium, while minimizing the typical issues.

Rockwool can be recycled and reused and has excellent drainage properties. It can support a more limited population of healthy biological inoculants, making low suspension mineral based nutrient formulas generally most suitable for this medium. With some exception, this inert medium is typically inhospitable for common Cannabis insects such as fungus gnats.  There is also available literature and research on growing plants in rockwool, as it’s a very commonly used medium in hydroponic food production.


As we continue to move through the mediums with increasing drainage capacity, compared with the aforementioned, this is the highest of the category when using a medium beyond the nutrient solution alone. So, if coco is the closest in consistency and drainage capacity to soil, stones are the furthest. Evolved and innovated from the predecessors, which used unsustainable expanded clay pellets, Growstones are sourced from recycled glass. Much like the name entails, they are small nuggets of porous spun glass available in multiple sizes and very easy to recycle. I’ve had mine in constant use for six years I think. Their porosity makes for a more favorable rooting environment than clay, with even higher drainage due to the uneven shapes they come in.

Stones provide some decent surface area for regularly applied inoculants to colonize. The are well adapted for multiple irrigation styles and able to provide a large number of nutrient application cycles daily. I like to think of this as the most hydroponic of the medium based methods, simply because it is closest to the naked roots soaking in solution on account of the high need for frequent irrigation.


While this technique is not widely used among today’s Cannabis farmers, it’s still quite a viable method for producing bountiful hydroponic harvests using only the nutrient solution itself as the medium. In this method, the plants are suspended in what are usually smaller net pots that are inserted into a narrow, covered tray allowing the roots to grow from the pots and out into the tray. The tray is placed on an angle that allows nutrient solution, pumped into the highest point, to slowly and evenly slow down the channel of the narrow tray bathing the roots in the very shallow flow of nutrient solutions.

Removing all medium between the roots and the solution has some intrinsic benefits as well as its own set of deficits. With no medium outside of the solution, the number of common Cannabis insects is extremely limited as insects require oxygen and aren’t suited to thrive in an all aquatic environment. Making changes to the medium, cleaning, flushing and replacing it is all a matter of reservoir management—which allows for great controls when it comes to treating possible disease, water quality issues, pH and TDS swings, lock out, nutrient deficiencies and the like.

As we move down the list, each method relies more heavily on the mechanisms and technology being employed to create regular irrigation cycles. The nutrient film technique is no different and is still less forgiving. Unlike all the methods reviewed so far that utilize medium of some kind which holds at worst a minimal level of moisture for the roots to feed from, in any method where no medium exists technological or equipment failures must be identified and rectified within a few hours, in some cases, to avoid catastrophic crop failure. As a result, seasoned gardeners include redundancies and fail when employing such methods whenever possible.


Perhaps responsible for some of the most mind-bending yields and growth rates, a truly dialed in deep water culture system is an awesome sight to behold. This technique also uses only the nutrient solution as the medium however, unlike the nutrient film technique, which relies on the thin depth of the “film” of nutrient solution for surface level oxygen exchange to occur providing adequate dioxide levels, deep water culture systems provides each suspended plant site with its own bucket of nutrient solution. To ensure the roots that grow into the deep pool of solution don’t suffocate, dissolved oxygen is infused into the solution through a variety of methods, which may include air stones and an air source, fuming, recirculation, electrolysis or a combination of these methods.

These systems require low nutrient levels to thrive and, in my experience, can far and away out-produce any other method available by a meaningful measure.

In addition to this method being highly vulnerable to technological failures with fewer options and redundancy, the systems and equipment can be: cost prohibitive, require a baseline understanding of plumbing and water pressure management and is unique in its needs compared with other mediums which share a similar recipe for success. Apply the nutrient schedule associated with a rockwool garden to a deep water culture system and your plants will likely be suited for termination in a week or less, making quality resources and information on this method more scarce. Lastly, managing and balancing a culture highly saturated in dissolved oxygen is more akin to tending to a salt water or exotic fish and coral reef tank than anything else requiring nearly constant monitoring of virtually all available data points to maximize potential and avoid failure. As fast and impressive as this method can be, it can be equally fast and depressive at accelerating an issue from a noticeable problem to complete crop failure.


No hydroponic article on mediums would be complete until mentioning the infrequently employed but deeply cool sounding aeroponic growing method. This technique often uses the very same narrow channeled trays that a nutrient film technique system employs, however it delivers the nutrient solution through an array of sprayers that are servicing a pressured manifold. The system sprays nutrient solution on the naked roots at periodic intervals and delivers huge amounts of dissolved oxygen, by way of the delivery method alone, and doesn’t require all the extra devices most frequently found in deep water culture systems.

While these systems boast high growth rates, they also rely heavily on technology and tools to deliver nutrient solution to the roots. Once again, it’s with a more limited capacity for redundancy, and huge potential for catastrophic loss upon failure due to the speed at which drought stress sets it. These systems are also very often impractical for the Cannabis gardener simply because its most efficient application utilizes a huge number of sites to produce the canopy.

Out of all these methods, which do you prefer or project that you would find yourself thriving with? Are you someone who values low maintenance, ease of application with a reasonable buffer for mistakes? Or are you someone who wants to buy all the gadgets, monitors and devices and be regularly taking measurements, making adjustments and tweaking things to improve them if only but slightly?

Hopefully after reading through each of these descriptions you can find yourself in one more than the others. Gardening is an art form, and choosing the method is similar to selecting the medium you choose to express yourself through. Since you’re the only one who can know where you will be most fully self-expressed, choose wisely. If you have any questions regarding the various hydroponic mediums never hesitate to contact me at As always, happy gardening!