"mainly differ amongst each other in terms of the technological methods used to grow edible plants indoors. 1. The first one, , consists of growing plants on a neutral and inert substrate (e.g. sand, clay, and rock material), which is regularly irrigated by a liquid fortified with minerals and nutrients that are necessary to sustain plant growth. Hydroponic systems use 60-70% less water than traditional outdoor agriculture. They are widely employed by hundreds of thousands of commercial greenhouses and vertical farms throughout the world. 2. The second process of vertical farming is , through which plants are grown without the use of any soil (or soil replacement): their roots, hanging down in the air inside a closed container, are exposed to a fine mist of nutrient-laden water, regularly sprayed through a nozzle. While this is a relatively new method for growing edible plants – it was first developed in 1983 – it is increasingly employed by commercial vertical farms such as and Tower Garden in the US. 3. Finally, a hybrid method, , integrates fish production into the hydroponic growing scheme. More precisely, it uses fish waste as a nutrient source for the plants after treatment, operating as a closed loop ecosystem for indoor farming. However, this system’s complexity and high cost hinder its widespread use. The former two methods are the most common forms of ."