When you see photos of huge indoor cannabis grows, you’ll notice that some of them use water instead of soil as a growing medium. They’re using a technique called hydroponics, which allows plants to root in nutrient-rich water and thrive without a need for soil.
It’s less likely that you’ve seen an interesting twist on hydroponics, which is beginning to find favor among some cannabis growers.
It’s similar to the traditional method of soil-less cultivation, but the nutrients aren’t mixed with the water that’s used as a growing medium. Nutrients are supplied naturally to the plants.
This somewhat-odd way to grow cannabis is known as aquaponics — and the nutrients come from fish that are being raised in the water below the plants.
Weed and fish together?
It actually makes sense, and the growing method can produce more potent buds. Read on and we’ll explain.
How Does Aquaponics Work?
Back in the 1970s, scientists began researching and playing around with the idea of using plants as a “natural filter” in fish farms. Much of that work was done at the University of the Virgin Islands by Dr. James Rakocy, and at the New Alchemy Institute in Massachusetts.
The research evolved into a concept that would establish a symbiotic relationship between the plants and the fish farm. And by the late 90s, Rakocy had documented the commercial viability of using what was called aquaponics to raise both fish and plants.
There were several convincing reasons for growers to try this method of growing. It’s environmentally friendly, it conserves water, it mimics the natural proliferation of both plants and fish – and it can produce a better crop than hydroponics or soil growing.
The approach isn’t in wide-scale use yet, with just a few large-scale commercial aquaponics facilities in operation. But it’s become popular in schools, at community non-profit organizations, and in the home growing world.
In short, aquaponics is the creation of a miniature ecosystem. Fish produce nutrients like nitrogen in their waste. And the nutrients can be used by plants once they’ve been converted to a more friendly form by beneficial bacteria in the ecosystem. In return, the plants clean and oxygenate the water which is returned to the fish tank.
That’s the way it works in nature, and it’s been shown to work in controlled environments as well. More specifically, it works well with cannabis plants.
Aquaponics cannabis grow supplies the plants with most of the nutrients it needs, but there are ways to set up the system so additional nutrients like potassium and phosphorus can be applied directly to the plants without harming the fish. The only other thing that must be added to the environment is fish food.
Sound interesting? Here’s how to try it.
Growing Cannabis with an Aquaponics System
You’ll need some supplies to set up an aquaponics grow, of course.
There are complete systems you can purchase, but the less-expensive way to dip your toe (and your plants) into the water is with a standard fish tank and a pump with a timer. Some people use barrels or other types of containers, but it’s simplest to begin with a regular tank.
Fill it with water, and let it sit with the pump off for a couple of days. That will get rid of any residual chlorine.
Then add beneficial bacteria that you buy from a store (or just add high-quality, pure ammonia to the water), and cycle the system by running the pump with just water in the tank for a month or so. That builds up the microbes that will be needed to break down waste produced by the fish.
You’ll have to test the nitrogen and ammonia levels in the water regularly; before moving on, the levels should both be 0 ppm (parts per million). That means that the nitrogen has been converted into nitrate that plants can use.
If you’re just starting, the safest approach is to buy an aquaponics cycling kit. You can find them available online.
Once cycling is complete, it’s time to add fish to your tank. Ballpark figure: a pound of fish for every 5-7 gallons of water. Guppies or goldfish are fine, but you may want to use hardier species like koi, tilapia, carp, or trout. Don’t forget to buy fish food when you buy the fish; you certainly don’t want them to starve.
The Media Bed
It’s possible to grow your cannabis plants using the same approach that you would with a soil-less hydroponics system, letting their roots dangle into the water. However, as we’ve mentioned earlier, that makes it difficult to supply the additional nutrients the plants will need.
The media bed we’ll be describing makes the most sense. It’s called a dual root zone bed, with an “aquatic” layer on the bottom and a “terrestrial” layer above it.
Use a sturdy plastic or wooden tray, which will sit on top of the fish tank. You’ll need to drill two holes in the tray where you can fit two bulkheads (fittings for connecting pipes or hoses) for a “fill and drain” system. The fill hose will bring water from the fish pump into the bottom of the grow tray, the drain hose will drain into the tank below.
Cover the bottom of the tray with a layer of expanded clay pebbles and cover it with a layer of burlap or another water-permeable material. A layer of pH-neutral organic or living soil then goes on top.
This setup allows the roots of your weed plants to contact the water in the tray, while you can add nutrients to the soil (mostly in the form of organic fertilizer containing potassium and phosphorus) that might harm the fish if they were added to or drained into the tank.
If you’ll be growing from seed, it’s a good idea to start them before you set up your tank, so they’ll already be hardy seedlings. Otherwise, you’ll want clones that have grown large enough to have at least two nodes. You can use regular pots to hold the plants, but the net pots designed for hydroponic growing are the best choice.
Most strains will grow just fine in an aquaponics system but some thrive in water-based growing. Look for hydroponic-friendly strains like Amnesia Haze, Gorilla Glue, or Northern Lights, or do some research to find out if the weed you like is suitable for the grow.
That’s all there is to the setup. All that’s left is to grow your plants, enjoy your weed, and laugh about the days that you were stuck in the dark ages of weed growing.
Growing Cannabis with Aquaponics: FAQ
Q: Is there anything I should know about maintaining an aquaponics system as the plants grow?
A: There’s quite a lot, and it’s best to buy a book on the subject before you get started. One challenge is regularly testing and balancing the pH of the water. Plants like neutral pH levels around 6.0-6.5, but fish like the pH to be between 7.0-8.0. Another important task is regularly checking nutrient levels for the plants to be sure they’re getting the proper amount of nitrogen from the system. And proper temperatures are even more important for aquaponic grows than for other types.
Q: Is aquaponics growing as expensive as it sounds?
A: You can keep the costs lower by using old fish tanks and plastic trays, but yes, it’s more expensive than other cannabis grows will be. Aquaponics is cool and fun to play with, but it’s going be a pricy hobby. If you’re serious about it, your best bet is to first master hydroponic growing and then take the next step.
- Love, D. C., Fry, J. P., Genello, L., Hill, E. S., Frederick, J. A., Li, X., & Semmens, K. (2014). An international survey of aquaponics practitioners. PloS one, 9(7), e102662. 
- Turnšek, M., Morgenstern, R., Schröter, I., Mergenthaler, M., Hüttel, S., & Leyer, M. (2019). Commercial aquaponics: a long road ahead. Aquaponics food production systems, 18, 453-485.