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Aquaponics in the Teaching Garden

Updated: Apr 6, 2021

Have you ever heard of aquaponics before? Maybe you have heard of hydroponics. Both of these are alternative ways of growing plants without soil! In this post we will dive into some basics of aquaponics and see what it looks like in the teaching garden!

What is Aquaponics?

Aquaponics is an alternative way of growing plants along with fish! Aquaponics is cool because it actually uses less water than traditional growing methods - this is because the water is recycled through the system and only needs to be changed every few weeks.

Aquaponics is often confused with hydroponics but they are slightly different, both of them involve growing food without soil and with water. To grow plants without soil you need some type of grow medium - somewhere for the plant's roots to establish themselves. This is needed with both hydroponics and aquaponics and can be pearlite, gravel, or something else. In the teaching garden we have used two different types of grow medium - clay balls (pictured right), and growstones or crushed foam glass (pictured left).

Plants grown conventionally get their nutrients from the soil, but without soil plants need to get their nutrients from somewhere else. With both hydroponics and aquaponics, the plants are able to get their nutrients from the water. The main difference between hydroponics and aquaponics is how the water gets its nutrients. For hydroponics, liquid nutrients are often injected into the water and diluted. For aquaponics, something much more exciting is happening!

A little Aquaponics Science

The main difference between aquaponics and hydroponics is the use of fish. In aquaponics systems, fish waste is the main source of plant nutrients. So, we feed our aquaponics fish and naturally, they poop. As with any fish tank, the fish waste - which is high in ammonia - is toxic to fish and must be cleaned or filtered out to keep the fish healthy and alive. But this water isn't necessarily healthy for the plants either, which is where the bacteria come in. This ammonia-rich water is also home to certain types of bacteria. There are three main types of bacteria that help keep aquaponics systems running smoothly:

  1. Ammonia-oxidizing bacteria (Nitrosomonas): these bacteria convert the ammonia in the fish waste into nitrites.

  2. Nitrite-oxidizing bacteria (Nitrospira): these bacteria convert the nitrites into nitrates - which are basically nutrients for plants.

  3. Heterotrophic bacteria: these bacteria convert solid fish waste (aka fish poo) into micro-nutrients which are also helpful for plant growth.

Without these helpful bacteria our aquaponics system would not work properly.

So, now we have water that is rich in nitrates and beneficial micronutrients! This water is then pumped into the grow beds so that the grow medium and plant roots are basically submerged in this nutrient-rich water. The plants then absorb the nitrates and nutrients from the water allowing them to grow into healthy adult plants. These plants grow like any other conventional plants! We have grown tomatoes, cucumbers, lettuce, and many other vegetables in our aquaponics system and the food is indistinguishable from conventionally grown vegetables. Finally, the water leftover after the plants absorb their nutrients is kind of filtered, a little cleaner, and pumped with oxygen and is then sent back down to the fish tanks. Below is a helpful diagram that illustrates this cyclical process.

What does aquaponics look like?

Aquaponics systems come in a diverse array of shapes and sizes. They can be as small as one plant on top of a fish tank, or they can be huge commercial growing operations, and everything in between!

Aquaponics in the Teaching Garden!

In the Teaching Garden we are lucky enough to partner with the Harbor School on Governors island. The Harbor School is an awesome public school where the curriculum is based around the water front! So, students who attend this high school learn about aquaculture, marine biology, ocean engineering, and many other water-based subjects. The students in the aquaculture program grow little baby tilapia fish each year and at the end of the school year donate them to our aquaponics system where they spend the summer growing larger. Below are a few photos of our aquaponics system which is built out of a reused shipping container! We have four 4x4 foot grow beds on the top of the system which are usually covered with a plastic hoop (the hoop blew off last winter and we are in the process of putting up a new one). Below, we have two tanks which hold about 300 gallons of water each. We can hold about 50 tilapia fish total in both of these tanks (so about 25 fish per tank).

Here you can see our hungry tilapia enjoying breakfast.

The inside of the system looks like this. The water filters down from the grow beds through the buckets above the tanks. The waste water is pumped out of the tanks into the blue barrel you see on the left. The blue barrel is a swirl filter - the water in here is constantly swirling like a whirlpool. This swirl filter helps to filter the remaining solid fish waste out of the water before it is pumped into the grow beds.

Then the water from the swirl filter is pumped into a black barrel that pumps the water up to the top of the system. You can see that black barrel that pumps the water up here.

Since tilapia fish are tropical fish, they only spend the summers with us in the teaching garden. At the end of each summer we have done different things with the fish. Sometimes they go back to the harbor school, sometimes they are rescued and taken home as pets, and sometimes we partner with project renewal which is a non-profit organization that (among other things) works to help folks struggling with homelessness and gives them culinary arts training to help them land steady jobs. They came out to learn how to cook our tilapia fish - a fate which was sad for our fish but at least they went to a good cause!

Come check out our aquaponics system in person when the garden opens to the public on weekends from 12-4 between May and October.

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