The word "hydroponics" may conjure up images of complex systems of trays, tubes, pumps, and containers in the minds of those who know a little bit about this cannabis growing method, and that isn’t necessarily wrong. But there are, in fact, quite a wide variety of different techniques used, some of which require very little in the way of special equipment.
What is Hydroponic Cannabis?
“Hydroponic” simply means any method of growing that uses a nutrient-water solution rather than soil. This method could be something as basic as hand-watering pots of inert medium with a nutrient solution. More sophisticated systems with multiple pumps, timers, and reservoirs can take some of the daily labor out of hydroponic growing, but they require more maintenance and setup time as well as a greater initial investment.
Cannabis growers have been using different hydroponic methods for many years as a way to maximize yields and speed up growth, the two main advantages of soilless growing. What follows is an examination of the most popular hydroponic techniques systems and media supplies used in the cultivation of cannabis.
Which Hydroponic Grow Medium Should You Use for Cannabis?
While there are several types of hydroponic setups that don’t use any type of growing medium at all, many of them still use some sort of substrate to support root growth. Various materials all provide slightly different benefits (and drawbacks), so some thought should be put into choosing the right medium for your cannabis plants.
Although there are literally hundreds of things that can be used, from sand and gravel to wood fiber and sheep’s wool, here we’ll focus on the most commonly used and readily available products.
Perlite, Vermiculite, Pumice
These mined minerals and volcanic rock contain a great deal of air space.
- Perlite and vermiculite are superheated to create the finished product, while pumice is naturally aerated
- Considered inert media, vermiculite holds more water and less air than perlite or pumice
- Can be sterilized and reused
Made of leftover material from coconut husks, coco coir (or coco peat) is often used alone as a grow medium or as an additive in potting soil and soilless blends.
- Sustainable alternative to sphagnum peat
- Holds 1000 times more air than soil
- Contains cellulose, lignin, and potassium
- Reusable to an extent
Expanded Clay Pebbles
Little pieces of clay are baked at 2190* F until they puff up, creating an inert substrate that holds air well and doesn’t compact over time. There are differing opinions as to whether it can be properly sterilized for reuse.
Growstones are a recycled glass product that has similar properties to perlite but holds more air and water. They contain calcium carbonate.
The most commonly used medium, rockwool is made by spinning molten rock into single filament fibers that are then bundled into blocks or slabs.
- Inert, holds water well and has very good capillary action
- Very slow to dry out, which can lead to root rot if overwatered
- Inexpensive, effective, but not reusable.
These mixes often mimic potting soil in their appearance and usage, but do not contain things like humus, compost and other nutritive ingredients.
- Generally comprised of things like sphagnum peat, coco coir, perlite, bark, and vermiculite
- Much greater air capacity than soil leads to better root development
- Can be reused, but not easily
Hydroponic Growing Gardening Systems and Techniques for Cannabis
Once you’ve selected your medium, it’s time to choose a hydroponic growing technique that suits your needs.
The simplest of hydroponic systems, run-to-waste, is the method in which the nutrient-water solution is applied periodically to the medium either by hand or through an automated system, and any wastewater is either discarded or stored and filtered for later reuse.
This system's most basic version is simply hand-watering pots of soilless mix or other media with the nutrient solution. Other setups involve plants in some sort of drain table with a reservoir, pump, and timer to deliver the solution at regular intervals.
Flood and Drain
Also known as “ebb and flow” or sub-irrigation, this method uses trays or specialized pots that are filled from underneath using a reservoir, pump, and timer (and sometimes a control bucket equipped with float valves), then drained back into the main reservoir. In addition to being one of the simplest automated hydroponic designs, many different media can be used in this system with good results.
Deep Water Culture
Deep water culture (DWC) is the technique of suspending the plant’s roots over an oxygenated nutrient solution, with some of the roots exposed to air above the water. In cannabis cultivation this is generally done with small net pots of grow medium placed in the lids of pots or buckets containing nutrient solution and aeration devices such as air stones connected to an aquarium pump.
High oxygen levels in the root zone make for very rapid plant growth with this technique. One variation, called top-fed DWC, uses water pumps to pump water over the roots; this is helpful in the early stages of growth when the roots have not grown down into the solution yet.
Continuous Flow Solution Culture
Continuous flow solution culture refers to any method that is constantly irrigating the plants with the water-nutrient solution. This can be achieved through a simple drip system, where a constant dribble of solution is delivered to each individual plant like a custom sprinkler system.
One of the more advanced methods is nutrient film technique (NFT), in which a constant flow of nutrient solution is recirculated through the bare roots of the plants, which are often placed in small openings in tubes or channels that are at a slight angle to allow for natural water flow. A pump in the reservoir constantly recycles the nutrient-water solution to the highest point in the setup. Care must be taken to get the flow rate right, as too little will result in the failure of the last plants in line, and too much will prevent any of the plants from successfully absorbing all the necessary nutrients.
With aeroponics, nutrient solution is applied to the roots of the plants in the form of a spray or mist. This method does not use a medium and requires external support structures such as cages or trellises to support larger plants. With the proper equipment, this method provides the most oxygen to the root zone of any hydroponic technique, leading to very rapid growth. In the cannabis industry, aeroponics is most frequently used in cloning machines to propagate new cuttings.
Now that you’ve been acquainted with some of the most common hydroponic media and systems to use for your next cannabis grow, we want to hear from you. Have you tried hydroponic growing techniques before, either for cannabis plants or other grows? Share your advice, tips, and questions in the comments section below!