|Hotel Verde’s aquaponic herb garden|
An aquaponics system makes it possible to grow food using about 90% less water than traditional gardening, and without having to use artificial fertilisers or even soil. Instead the system relies on a symbiotic relationship between aquatic animals and plants.
Aquatic animals such as fish or prawns are raised in tanks. Bacteria break down the waste they excrete, along with uneaten fish food, into nitrates and nitrites. These serve as fertiliser for plants, which are grown hydroponically, in nutrient-rich water rather than soil. In turn, the plants clean the water for the animals.
This type of system is special because it’s self-sustaining and creates very little to no waste. People can harvest both the plants and the fish.
At Hotel Verde, we have a vertical aquaponic garden, designed to save space whilst allowing for the efficient production of small edible plants. Depending on season and demand, we grow plants such as celery, spinach, chives, watercress, basil, butter sage, lettuce, mint, pansies and parsley.
The aquaponic system is fed by a timed pump system, to ensure that the plants get enough water without wasting unnecessary energy.
Aquaponics at home
You can build a basic aquaponics garden at home, using readily available and fairly inexpensive components.
What you’ll need:
one or more fish tanks
grow beds or vertical pipes to contain the plants
suitable growing medium for anchoring the plants
a water pump for circulating water through the system
an air pump or another mechanism for oxygenating the water in the system before it flows back from the plants to the fish tank
plumbing components, to allow water to be directed through the system.
Inexpensive options for fish tanks include concrete tanks, stock tanks or even large barrels. Note that you mustn’t fill the tanks with chlorinated water, which will kill nitrifying bacteria. Instead leave water standing for a few days and the chlorine will naturally leave it as a gas, or use a dechlorinating filter.
It’s recommended that when you start an aquaponics system, you aim to stock about half a kilogram of fish for every 3.5 litres of water. Types of edible fish often used in aquaponics systems include tilapia, catfish and, during the cooler months, even trout. You can also use non-edible species like goldfish if you choose.
You can construct grow beds using concrete, plastic flood trays, wooden crates lined with pond liner or even old bath tubs. The beds should be a maximum of ten times the surface area of your fish tank(s). As an alternative, you might choose to suspend lengths of PVC pipe, drilled with evenly spaced holes for holding plants. This type of system means you won’t need much space but more complicated plumbing will be required to flood the pipes at regular intervals.
The grow beds must be filled with an inert growing medium, such as fine gravel (provided it won’t cause pH problems – drop in vinegar and test that it doesn’t bubble), perlite, coco coir or pH-neutral clay pellets. This medium anchors the plants.
To circulate water through the system, you need a pump. Generally a magnetic drive pump is a good choice because it ensures that oil won’t leak into the tank. A solar pump would make the system almost completely self-sustaining.
For plumbing, you’ll need fittings and tubing for circulating water between the fish tank and grow beds. You’ll also need a system for regularly flooding the grow beds. One good option is to use a network of PVC pipes, spaced about 30 centimetres apart on the beds and with small holes drilled about every 15 centimetres along their surface. You can then plant a seedling in each of the small holes. A timed pump is also useful.
Once the system has been set up, you’ll need to find the right balance, feeding the fish the correct amount and growing the right quantity of plants to clean the circulating water, given the amount of nutrients produced by the fish. It will take the nitrification bacteria that breaks down the fish waste into fertiliser about a month to become established.