Hydroponics is a catch-all term which may literally translate to “water working,” but is generally understood to mean “any gardening method that doesn’t involve growing in soil.”
Plants have needs that must be met in order to grow. The above-ground leafy portion requires access to light and air, and the below-ground root portion needs access to water, air, and nutrients. Fortunately, cannabis is flexible as to the specifics of how those needs are met and can be grown via a variety of methods.
Growing Marijuana in Soil — Mother Nature’s Way
Under the right conditions, cannabis can grow and maintain a population year after year without any interference from humans. In its native habitat, cannabis sprouts in the spring, grows through the summer, produces seeds during the fall, and the cycle repeats again next spring. It receives sunlight, gets moisture from rain and nourishment from the soil. Nature has full responsibility for the care of such plants and no human intervention is needed. This hypothetical cannabis would be about the most “natural and organic” marijuana one could imagine. That’s one end of the organic-hydroponic spectrum.
The further a growing method veers from this organic ideal, the less organic it could be considered, although quantifying that can be tricky.
The good news for the natural-organic side is cannabis enjoys a wide climate range and can grow for years completely naturally in many areas around the globe.
Natural soil is comprised of mostly minerals with some organic material mixed in and works well as a planting medium in fields and garden plots, but tends to be too heavy for use in containers or indoors. The use of soil for growing plants disqualifies them from being hydroponic. Soil-based grows are those using actual dirt to provide an anchor for roots and supply nutrients.
For cannabis plants grown in containers, a soil substitute is generally used. These soilless mediums include ingredients such as coco coir, peat moss, perlite, etc., which are lighter and work better in containers. The experience of using them is similar to using soil, although since actual soil is not involved, they technically qualify as hydroponic.
Imagine a second hypothetical cannabis plant grown on a not-too-distant-future space station. Every aspect of its life is controlled and artificial. Roots in a soilless grow medium, or in no medium at all. Food and water intake is measured to the milligram and milliliter, with light exposure controlled to the second. Carbon dioxide exposure is calculated with each nutrient solution computed, concocted, and controlled. It’s an environment where plants could not survive even a short while without human intervention. It’s a place where a gardener bears the primary responsibility for meeting the plant’s needs and not doing so results in trauma and death for the neglected plants. That’s the other end of the spectrum — where plants are totally dependent on the grower.
For practical purposes, most gardeners use methods somewhere between these two extremes.
Since all configurations have some way to supply water, nutrients, and air to the roots that is one way to compare methods.
In soil, the dirt is watered which carries nutrients to the plant roots. The soil is allowed to dry out between waterings to give the roots access to air.
Although technically a hydroponic method; using a potting mix is similar, although it tends to dry out faster than soil does, giving better access to air, but requiring more frequent watering.
Growing Cannabis Without Soil
In more stereotypical hydroponic systems inert material such as clay pellets can be used. Clay pellets dry out very quickly, so they require near-constant watering. Drip systems often use clay pellets since they are difficult to overwater and provide plenty of airspace in the voids between the pellets.
Stonewool is another inert material but unlike clay pellets, it holds water well so doesn’t need to be watered as often as clay pellets. Stonewool is often used in flood and drain (a.k.a. ebb and flow) systems where a nutrient solution is added to the tray holding the plants to supply moisture (the flood or flow), which is then drained to give them access to air and prevent the roots from drowning (the drain or ebb).
If the plants are placed in nets, they can be grown hydroponically in nutrient solution. Deep water culture (DWC) systems spray air into a nutrient solution that the roots are suspended in. On the flipside, aeroponic systems spray nutrient solution into the air that the roots are suspended in.
Nutrient film technique (NFT) is a hydroponic variation where plants are suspended in channels and nutrient solution is gravity fed down a fibrous mat in contact with the roots. The roots are exposed to moisture from the mat and air from the space in the channel.
There are several variations on these themes, but all hydroponic (and non-hydroponic) systems will have some way to supply the roots with nutrient solution and air. Determining how a hydroponic system will meet these needs can go a long way toward understanding how they work (and what may be going wrong when they don’t).
When choosing what method to use, remember that the further away from nature (and the closer to the space station) a style gets, the more control is put into the hands of the gardener, which can either be helpful or hinder the final harvest. A skilled gardener, when handed increased control, can increase yields. Too much control in the wrong hands, however, can be devastating with organic methods tending to be milder and more forgiving of small errors.
Which method of gardening is best for a given situation depends on a lot of factors. Available resources, gardener skill level, environment, and desired outcomes all play a part in figuring out which styles of growing are best suited for a given situation.