Our first article presented an overview of hydroponics. It discussed some of the benefits of these grow systems, and advantages of growing indoors. Now we will dive into the details.
Hydroponics is the practice of growing edible and non-edible plants without the use of soil as a growing medium. Traditionally, hydroponics utilizes a fully recirculating system, in which nutrient-laden water is kept in a ‘source’ water tank, that is either hand mixed or mixed by automated, computerized systems that also keep pH at a targeted ideal level.
The ‘source’ water is then pumped from the tank into hydroponic structures where the plants here held, then it drains and returns to the source tank to complete the cycle. Most hydroponic systems do this without human intervention. Capturing and recirculating effluent can generate up to a 95% reduction in water consumption during cultivation. In an era when natural freshwater sources are being rapidly depleted, worldwide, this is an important reduction.
The structures that hold the plants themselves can vary greatly, separating hydroponics into multiple variations. The most common types of hydroponic systems are Deep Water Culture (DWC), Nutrient Film Technique (NFT), Aeroponics, and Ebb and Flow systems.
DEEP WATER CULTURE
First, let’s dive into Deep Water Culture (DWC), one of the more frequently used methods in commercial hydroponics. DWC structures are long, narrow rafts made of wood with pond liner, or extruded plastic troughs. These containers range in depth from a few inches up to twelve inches deep. With a deeper trough, temperature and pH are more stable since there is a greater volume of water, which needs a more dramatic fluctuations in nutrients, pH level or temperature to change overall levels. Because water is heavy, a deeper trough is far heavier than a shallow trough. Trough depth will depend on how stable your environment is, as well as how much weight your support structure can handle.
Polystyrene ‘rafts’ floating on the water in the trough hold plants at a predetermined spacing, with their roots fully submerged in the water. The water in the raft flows in at one end, and out the other, with air pumps keeping oxygen levels saturated all the way along the trough. Growing plants need large amounts of dissolved oxygen to stay alive, since their roots are always submerged in water. This need for oxygen can lead to catastrophic issues if the power supply (and therefore oxygen supply) is interrupted. That is the biggest downfall of DWC, because a drop in dissolved oxygen (DO) in the water can kill the plants in hours. On the other hand, when operating effectively, DWC systems require very little maintenance if properly set up, and they are known to produce some of the fastest growth rates with minimal labor requirements of all the hydroponic techniques.
Dutch buckets or ‘Bato Buckets’ are a form of DWC that uses 5-gallon buckets plumbed together in a recirculating fashion with each plant growing in its own bucket. Water is oxygenated either at the source water tank or at each individual bucket that is supplied with an air stone. Dutch buckets are cheap and easy to set up and are preferable for larger format plants over the ‘trough style’ DWC technique.
Next to consider is the Nutrient Film Technique or NFT, a favorite method for many commercial growers as well as home growers!
NUTRIENT FILM TECHNIQUE
NFT structures are lightweight, highly customizable, and can be built with easy-to-find materials like PVC or ABS pipe. Since they’re so light and easy to modify, they are often assembled into modular units that can be disassembled easily for cleaning or to relocate them to a new growroom!
NFT uses much less water than other methods. It requires only a small trickle (or film) of nutrient-laden water flowing through long channels of PVC pipes, to support a single row of plants spaced along the length of each pipe, with the pipes spaced within a few inches of each other side-by-side, to create the most growing space for your floor space as possible. Ease of access and use of common materials for these systems makes them quite affordable and easy to build as well!
Multiple runs of the long PVC pipe usually meet at one, larger, drainpipe at the lowest end, which returns the water to the nutrient source tank, and then it gets pumped out again to the high end of the pipes, with gravity doing most of the hard work of irrigation. A high ratio of air to water in these pipes allows the roots to directly access oxygen, decreasing the dependency on oxygen supplementation with electric air pumps. This makes NFT systems less risky for plants.
The low water volume needed in these systems does means that water conditions can be thrown off more easily, leading to a potential for pH spikes, nutrient fluctuation, and more commonly, temperature swings. If you build an NFT system, you will need to be sure that fluctuations will not occur (or that you are prepared to fix them, in a timely fashion.)
Aeroponic systems tend to be complex and costly to build, but they boast some of the highest yields, lowest water use, and fastest growth rates! How do they achieve this? As in the other methods listed above, oxygen plays a huge part. There is tons more oxygen and nutrients available to the plants in an Aeroponic system. Standard ‘hydroponic’ systems are those that use water (hydro) as the growing medium, whereas Aeroponics relies on air as the primary growing medium.
In Aeroponics, plants are suspended over a trough (or other water-tight container), with their roots dangling inside an open, empty container below them. A “Mister” or “Fogger” is placed at the bottom of each container to spray water upwards towards the roots, delivering water and nutrients in droplet form. More sophisticated Aeroponics systems reduce droplet size more effectively than more simple, cheaper systems. Cost and efficiency are interdependent. The smaller the droplets, the better!
In droplet form, water and nutrients are not only delivered faster to the roots, but they’re also absorbed more efficiently, leading to lower water use and lower nutrient costs. Far more oxygen is available in the mist (or fog) than in a system with submerged roots, and the oxygen is available at all times, without the need for dedicated air pumps to saturate the water with oxygen.
Increasing nutrient uptake efficiency leads to vastly increased growth and higher yields, making this a sought-after commercial technique used for indoor growing. Aeroponic systems are costly to build, require a lot of maintenance, and involve a lot of careful design considerations.
The three methods described above are great for production of smaller, quick-turnover plant crops.
However as you might imagine, larger plants require more space and need sturdier support structures. Large plants tend to grow higher, so they become more top-heavy, which can cause them to topple over or fall out of the kinds of structures described above, unless they are properly secured with stakes, lattices, or supporting strings/ropes.
While these types of plant supports are common in Dutch bucket systems, most of the other methods aren’t ideal for growing large plants. This issue can be solved by using a type of system called “Ebb and Flow.” Ebb and Flow systems are often paired with another type of indoor growing called “Aquaponics”. Aquaponics is one of my favorites developments in agriculture, with a history stretching back hundreds of years.
But that subject deserves an article of its own, so we’ll save Ebb and Flow systems and Aquaponics for the next article in this series. Stay tuned!