Soilless farming or hydroponics is a technique for growing plants that dates back to 600 BC. It uses a nutrient rich water solution instead of soil to deliver the mineral requirements that the plant needs to thrive. Sunlight is required of course whilst carbon, hydrogen and oxygen are provided from the air and water. In mineral form they’ll need Nitrogen, Phosphorus, Potassium and a long list of other elements in smaller quantities, some of which have long names that are quite hard to pronounce; like Molybdenum.
What exactly is soil and how can we go without it?
Soil is a few things. To be specific, gas, water, minerals, organic matter and living organisms. The gas make up is very similar to air as you might expect. Nitrogen, carbon dioxide and oxygen albeit slightly heavier on the carbon dioxide than air. The minerals come in three size classes of clay, silt and sand which absorb water and inorganic nutrients and provide an anchor for plant roots. The soil organic matter is plant, animal, and microbial residues in various states of decomposition. And finally, the living organisms include bacteria, algae, earthworms and other insects which all assist to break down the organic matter into an inorganic form that the plants can absorb. To clarify here, plants only feed on inorganic matter.
So in a nutshell, hydroponics basically delivers the nutrients to the plants in solution form, bypassing the need for the organic matter and the living organisms required to break it down. These nutrient solutions are relatively stable, evenly distributed and delivered instantly in a form that the plant can consume, rather than dependent upon the quality of the soil which comes with all sorts of unknowns and can take a good deal of work to get right. Hydroponics are also very well suited to indoor farming. No soil means no mess and no insects and it’s also possible to explore vertical growing arrangements that save space!
Hang on a second. Don’t the roots need something to sit in?
Yes! A growing medium is required for this and there are a few options out there. One is rock wool which is a blend of rock and chalk that is heated up, spun into fibres like candy floss and then shaped into cubes as shown below with the fennel.
Another example is coconut coir which is primarily made from the husk fibres of a coconut shell with a few additions to help it drain. The example on the right is wrapped in something that resembles a tea bag that keeps everything all in place whilst allowing the roots to peek through.
There are many other examples out there but ideally you want something that :
- Has air and water holding capacity
- Binds well with nutrients (good cation exchange properties)
- Is pH stable
- Inexpensive and lightweight
- Organic, biodegradable and environmentally friendly
Of the two examples illustrated here, the rock wool has been used extensively in the past due to its high water retention properties whilst providing a good anchor for larger plants. However, it comes with a slightly high pH and critically for some, it is not biodegradable and will sit in a landfill for 10,000 years. The coconut coir was up until recently considered an agricultural waste material that would otherwise go unused, has even better water retention properties than rock wool and is a certified organic material that will decompose!
At Grobrix we are always looking for more sustainable ways to grow our produce and so far, we like what we see with the coconut coir ! It currently performs very well on our indoor vertical farming system and we love the fact that it biodegrades!
A bit more on those Nutrients
Nutrients are to hydroponics what fertiliser is to soil. They can be synthetically or organically created. The key macro ingredients are Nitrogen, Phosphorus and Potassium or N, P and K. Here’s a quick summary of what each one does!
- Nitrogen is absolutely essential for leaf development and is required from an early stage of plant growth for the plant’s colouring and chlorophyll production. If your plant is lacking, a common sign will be the yellowing of the leaves and weak stems.
- Phosphorus is needed particularly by young plants when forming their root systems and by fruit and seed crops. Root vegetables such as carrots, swedes and turnips obviously need plentiful phosphorus to develop well. If your plant is lacking, the symptoms that show will be a reddish purple colour on the leaves and low fruit yields.
- Potassium (aka Potash) promotes flower and fruit production, so often the supply of this is increased once a plant reaches fruiting and flowering stage when the building of starches and sugars takes place. It is also essential in helping plants to better resist disease. It can naturally be found in wood ash which is where the term ‘Potash’ actually comes from and if your plant doesn’t have enough, you will see little by way of fruit!
So to wrap up and reiterate on this, ammonium is ammonium whether it comes from fish excrement or from a laboratory. The plant is completely indifferent on the origin and will happily absorb it either way. So the key questions you want to be asking yourself with regards to your produce are not really organic versus non organic but rather :
- What is my chemical pesticide exposure?
- Was it grown sustainably?
- Was it grown locally?
And the best way to be 100% sure of all of these…. is to grow it yourself!
Interested to learn more about the different types of hydroponic systems for indoor farming or gardening? Grobrix offers solutions for simple, functional, and space-efficient plant growing systems.