How Do Media-Free Systems Work?
Media-Based Systems vs. Media-Free Systems
In the last episode, we covered the basics of media-based systems.
We focused especially on the surface area in different types of systems, as specific and biological surface area are both crucial to understanding the functions of an aquaponic system.
Today we’re talking about using media-free systems like raft, aeroponic, and sometimes NFT when building an aquaponics system.
We’re going to talk about the nuts and bolts of these systems and whether or not they are suitable for beginners.
Four Types of Media-free Systems
First, let’s talk about what a media-free system is.
In these types of systems, the roots hang freely in the water or the air rather than in a growing medium like hydroton or crushed granite. Today we’re going to talk about four main types:
- Raft systems
- Deep Water Culture systems (DWC)
- Nutrient Film Technique systems (NFT)
Raft and DWC Systems
Raft and deep water culture systems are very similar.
In these systems, plants float on rafts on the water and the roots, which dangle in the water, take up nutrients in the water. These are both very common in commercial aquaponics. This isn’t a bad way to grow, especially if you’re looking for an inexpensive hobby method.
There are, of course, pros and cons.
Rafts and DWC systems are cheap to get started with and suitable for many common and valuable food crops. Another benefit is that the large amount of thermal mass means fewer variations in temperatures of the root zones. (If you didn’t already know, root zone temperature is important to keep steady.)
This makes it especially suitable when you are growing in the tropics. A downside of this is that it’s very difficult to scale, (labor increases drastically) which makes it less practical in a commercial setting.
NFT (Nutrient Film Technique) is another media-free technique.
The only media in the system is the soil from the plugs that you use to transplant the seedlings. The seedlings are planted into troughs that are irrigated from one end. The solution flows down this trough in a very shallow stream (a film), and as the seedlings mature, the roots grow into a mat at the bottom of the trough. NFT is often considered a form of aeroponics.
With NFT, you want to try to figure out the happy medium between having enough water and too much.
Too much and you will damage the root hairs. Too little, and you’ll have nutrient or oxygen depletion from one end to the other of your trough.
Often, because the plants at the irrigated end of the trough are consuming dissolved oxygen, the drainage end of the trough will not have enough. Another common problem is that solids accumulation in the root mat near the end of the trough where the flow of water is too weak to flush solids away. These two problems often result in root die back and poor plant health.
If growing with NFT, you have to think about the length of your trough and about flushing solids.
Aeroponics is the culturing of plants in such a way that the roots dangle in the air.
The plants receive nutrients and water through a mister. (Misting is necessary, as stronger force would harm root hairs.)
The biggest drawback of aeroponics is that the root zone temperature tends to be very unstable because there is no thermal mass surrounding the roots. The air around the roots heats and cools quickly. As the root zone heats up, the roots suffer, not just from the heat, but from the lack of available oxygen.
Aeroponics presents some challenges. You cannot use aquaponics for aeroponic growing because the irrigation needs of an aeroponics system are very high, and it can be difficult to get well-filtered water that will mist all day and not foul. For this reason, aeroponics is limited to hydroponics.
Root Zone Temperatures
You’ll see different types of systems in different climates. This is largely due to root zone temperatures.
Raft and DWC are common in tropics and south, but as you move north, you’ll see mostly NFT.
NFT is more space and labor efficient.
There’s a trade-off between warmer and colder water. The colder the water, the more dissolved oxygen in the water.
Cooler water is usually healthier for roots- if you want to maximize oxygen at the root level, you’ll want to run your water at the bottom of the crop’s ideal range.
That will make sure that the solids decomposing in the root zone are not consuming too much oxygen and creating anaerobic zones.
Having said that, it’s pretty tough to get anaerobic zones in aeroponic techniques. But it is still possible to have anaerobic zones and root die back even in NFT techniques.
So when you’re using these techniques, you need to be careful about keeping the roots aerated.
Filtration in Different Systems
Filtration is necessary in media-free systems; otherwise, solids collect around plant roots and cause problems. Filtration may be passive or mechanical.
An example of passive filtration would be a settlement tank, where solids accumulate on bottom of the tank and are removed.
Mechanical filtration may be a polygeysers or a bead filters, where water is pushed through a filtration contraption. Mechanical filtration requires and under-pressure plumbing operation.
Something to remember is that the type of system you are using decides the level of filtration that you’ll need to apply. In aeroponics, for example, there can be no solids, since you will be using a mister.
Microbes in Different Systems
Most of these systems require supplemental bird netting or another source of BSA for the microbes. Many of these systems have something called mineralization tanks, which are basically biofiltration tanks. The microbes live on plastic, aggregates, or bird netting (this is a common one) and mineralize the solids that are slowly washed through the tank with the system water. Bead filters also work to provide BSA.
You might be thinking, “What about plant roots? Don’t they provide BSA?”
Plant roots do provide BSA, but it takes a while to establish the microbial population. Every time you harvest, those microbes have to re-establish. This makes roots more of a supplemental source of BSA, but not something that should be relied upon.
In media free systems, you are limited to smaller crops that need relatively small amount of anchoring. No vining pants, squash or eggplant, tomatoes, etc.
Keep in mind that larger plants consume many more nutrients. You need to be really careful with this. (Nutrients are typically less available in media-free systems to begin with, so using large statured crops can be dangerous.)
I don’t suggest using large-statured crops in media-free systems.
Which Is Best For Beginners?
We’ve tried a few aeroponic, NFT, and DWC techniques. They can be very useful- both aeroponics and NFT can be light weight and pretty easy to assemble, with low upfront cost. (DWC is the cheapest usually.)
The thing you want to think about is choosing a system for your needs. Anymore, we grow completely with towers because of our needs, as the towers let us do live sales and that is what the market calls for.
DWC is good on a budget. It’s accessible. But in the end, we find that for beginners, a media-based technique is the best way to go.
Media-free systems are tricky and there’s a lot of room for mistakes.
Media-based systems are much more forgiving, and the crop range tends to be much wider.
So if you’re just starting, look into towers and other media-based techniques. It’s the best way to get started.
Thanks For Tuning In!
If you have any questions on types of systems, check out Episode 4.
Thanks for joining us today in Aquaponics Academy, a podcast dedicated to teaching new techniques and helping listeners overcome obstacles with their aquaponic systems.
If you enjoy this podcast, please think about leaving a tip on our podcast website to help us to continue producing the podcasts. If you are interested in starting your system with ZipGrow Towers or adding them to an existing system, feel free to check out our product line at ZipGrow.com.
Tune in again!