Lars Lund

08 Sep 2020 14:33

Grow in water and fertilize with fish

Do you like technology, then cultivating without soil might be just the thing for you

Hydroponic systems are all different. They range from small systems you can have in your window ledge to larger systems that fit into your greenhouse. If you only cultivate in water, that is, without a growth media, it is called the aeroponic method.

A growth media covers a wide range like for example stone wool, Rockwool, perlite, coconut fibres, clay pebbles or LECA which all drain water. The media is, as opposed to the soil which contains minerals and fertilizer, an inactive matter which does not nourish plants. All the nutrients the plants need comes from a nutrient solution that is mixed in the water. The trick is that you are then able to control exactly what the plants get. When cultivating in the soil there is a risk of the plants not getting what they need, and the plants can then turn sick. Also, in the water-system, there are no harmful soil bacteria or flea beetles that harm the plants.

Instead of adding fertilizer you can do as Søren and let the fish fertilize the water. Besides the nutrients, it is important that the water you use have the correct pH value. If the pH value is not correct then there are matters that the plant cannot absorb, no matter if you cultivate in soil or hydroponic systems. The advantage of the hydroponic systems is that you quickly can adjust and control the pH value.


From simple to advanced

Most pastime hydroponic systems basically consist of a deep tray for the plants, a reservoir of water and fertilizer, a submersible pump which pumps the water to the plants, an air pump for oxygenation of the water and the nutrient solution, and then maybe a source of light for extra light when it is dark or if you cultivate inside.


Examples of systems


The simple system has a wick that goes into the reservoir and brings water to the growth media. There is a pump in the reservoir which aerate the water. It is a system like the capillary boxes without a pump. The disadvantage is that the wick is not always able to carry enough water for the plants.

Water culture is another system. Aeroponic is the technique that doesn’t use growth media but only a reservoir. He reservoir is filled with water and fertilizer and an air pump to aerate the water. You then put a polystyrene platform on top which floats on the water. In the polystyrene platform, there are small holes for the plant’s roots to reach the water. The system is well-suited for salads and plants that need a lot of water.

A third system works the way that you have a reservoir of water with a grow tray filled with growth media and plants on top. From the bottom reservoir, the water is pumped through the main hose (the bold hose) which split into drip lines. In the reservoir is another pump that aerates the water. The excess water that the plants don’t need drips back into the reservoir.

You can put a timer on the pump to adjust the amount of water that is necessary. In this system, you reuse both water and nutrients, but this is also the disadvantage of the system as you then might fertilize too much. You can get equipment for measuring the pH value and the fertilizer solution.

The advanced one but still quite simple system is the so-called “nutrient technique system” which is the system that cultivates only in water. It looks like the drip irrigation system from the greenhouse but without actual media. The plants are in small pots that fit in the polystyrene platform’s holes. The water is then pumped in the reservoir and irrigates the roots in a steady stream, so they get the water and nutrients they need.


The most advances system in the aeroponic method is a sprinkler system. The technique is basically the same as the other systems, but the big difference is that the roots are not in contact with water. The water and nutrients are sprayed on the roots through the mist nozzles, so excess water runs back into the reservoir and is reused. The disadvantage is if the mist nozzles break down, then the roots will dry out.

Try it yourself

You can buy these different systems all over, but you can also start small and make your own. Many starts with a gutter or a drainpipe which is closed in both ends. The water is pumped into the gutter or drainpipe with a hose from a reservoir. The water then flows through the roots and back to the reservoir to get reused.