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Beyond Soil - Understanding the Fundamentals of Hydroponics

Beyond Soil - Understanding the Fundamentals of Hydroponics

Hydroponics is an umbrella term for soil-free methods of cultivating plants indoors and outdoors. In its basic form, each plant sits in a growing medium in a net cup and its roots are immersed in a water-nutrient solution. Hydroponic systems are closed systems and thus save our most precious resource, water, and can reduce our environmental footprints from CO2, nutrients, and pesticides. Hydroponics can be a highly effective method for growing plants, as it enables the close monitoring and precise control of all the important parameters such as nutrient concentration, oxygen and pH levels. This leads to faster growth, healthier plants, and higher yields. Hydroponic systems can grow a wide variety of plants, including vegetables, fruits, herbs, and flowers. Together with an optimised LED lighting system, indoor hydroponics allows for year-round cultivation, regardless of the season or weather conditions, making it possible to grow fresh produce where it would otherwise be impossible.

In this article, you will get to know the most popular types of hydroponics, learn about their benefits and shortfalls, and how you can grow your own delicious ingredients. Visit our shop and discover our hydroponic system APPA. We are confident that you will be thrilled with the ease and efficiency of growing with hydroponics.

There are several different types of hydroponic systems, each with their own set of benefits and challenges.

  1. The Kratky method, named after Bernard Kratky, a researcher at the University of Hawaii, is the simplest form of hydroponics. It is a passive, non-circulating technique using a single reservoir filled with a water-nutrient solution. The plants are placed in net cups filled with growing medium, for example rock wool or coconut coir, above this reservoir. The roots grow through the medium and then directly into the nutrient solution. As the plants use up the solution, its level drops, so that the roots pass through a pocket of air before reaching it. The parts of the roots that are in the air develop thin, hair-like offshoots and are able to absorb oxygen, while the rest take care of the water-nutrient supply. This technique works best for leafy vegetables that are fast growing and do not consume large amounts of water.

    Pros: This method can be as simple as putting a plant in a glass of nutrient-rich water.

    Cons: Due to its passive nature, it is generally not possible to maintain the optimal environment, such as oxygen level, pH, and nutrient concentration, and this method does usually not work well for long-term or fruiting crops. As the water does not circulate, pests tend to thrive and the oxygen level in the reservoir drops, "suffocating" the roots and leading to rot.

    Many cheap hydroponic home systems employ this method. If the system has no pump, it either utilises the Kratky method or is a wick system, see point 3.

  2. A variation of the Kratky Method is known as the deep water culture or floating raft technology. In this setup, the water-nutrient solution is oxygenated using an air pump and an air stone, similar to ones used in fish tanks. There is evidence that the additional oxygen in the water leads to faster growth and healthier plants, mitigating the risk of diseases. This method is widely used in commercial farms for leafy greens and herbs with short lifecycles.

    Pros: It is almost as simple as the Kratky method and only requires an additional air pump. The added oxygen boosts growth and can lead to healthier roots.

    Cons: The problems outlined for the Kratky method essentially remain the same and are only slightly improved by the additional oxygen.

  3. The Wick system is another simple system with non-circulating water that uses long wicks of growing medium to ensure that the roots always have access to the liquid. The growing medium wick reaches from the top to the bottom of the reservoir. Even as water is used up by the plants and the water level sinks, the wicks always stay in contact with the water, soaking up the liquid. This allows for a constant and steady supply of water and nutrients to the plants, without the need for pumps.

    Pros: Like the methods above, it is simple to set up and does not require much maintenance. Since typically more growing medium is available in the long wicks, some suppliers offer hydroponic medium that already contains nutrients, eliminating the need to use a water-nutrient solution.

    Cons: The shortcomings of the Kratky system translate to the Wick system as well. With the oxygen supply in standing water declining over time and no ability to regulate pH and nutrient levels, this method is susceptible to mould and root rot.

  4. The ebb and flow or flood and drain method alternately floods and drains the root section of the plants with a nutrient solution. In addition to a water-nutrient reservoir, a second container is used to house the plants’ roots. Using a water pump, this container is filled up with the nutrient solution so that it can be absorbed by the roots and the growing medium.  After a short time, usually a few minutes, the nutrient solution is drained back into the reservoir. This flood and drain procedure is usually repeated several times a day. When the chamber is flooded, the oxygen-poor air in the container is displaced, and when it is drained, the roots are exposed to new oxygen-rich air. During the "dry period", the solution retained in the growing medium feeds the plant.

    Pros: The major benefit of this method is that the plants’ roots are not in constant contact with the water, reducing the need for oxygenation and the risk of pests and disease.
    It also allows the cultivation of larger plants with a longer lifecycle.

    Cons: This method requires a water pump to flood the chamber periodically, which introduces an essential point of failure. As the growing medium is soaked with the nutrient solution, the minerals will deposit in the medium. This often leads to fluctuations in nutrient and pH levels.

  5. Instead of filling up the root container, the nutrient film technique (or technology) continually circulates a shallow stream of water past the plants’ roots. This method is similar to the ebb and flow method in that it utilises water-nutrient reservoirs, root containers called channels, and water pumps. However, designs typically involve long channels that require paying close attention to the right length, slope, and flow rate to meet the plants’ needs. As the water circulates, it collects oxygen and passes it on to the roots. Since the roots continually receive fresh nutrient- and oxygen-rich water, it is possible to cultivate plants with very little or no grow medium at all.

    Pros: This method is very efficient. It requires very little growing medium and it is possible to monitor and precisely control the growing environment. The nutrient solution stays oxygenated through its continuous movement.

    Cons: Similar to the ebb and flow system, the nutrient film technique is susceptible to power outages or pump failures. As often only little growing medium is used, it takes only a few hours until the roots dry out and the plants die. The pump must run 24/7.
    This method is rarely suitable for large plants with long lifecycles, as the channels usually have a small diameter and cannot support the weight of heavier plants. In addition to that, the roots of long-term crops may block the channels.

  6. The drip method is very similar to the nutrient film technique. A drip system pumps the nutrient solution in short intervals through thin "drip lines" and a "dripper" nozzle directly onto the roots. As there is no continuous flow of water, plants usually require more growing medium to retain the nutrient solution in comparison to the nutrient film technique. However, this also allows the cultivation of larger plants, and the pump runs in small intervals only, giving almost all roots time to breath.  Not only commercial hydroponic farms, but also many farms growing in soil, use some form of a drip system as it is very efficient and water saving. 

    Pros: This method is very efficient, water saving, and it gives great control of environmental parameters. Drip systems often allow the cultivation of large plants with long lifecycles.

    Cons: Drip systems are at risk of clogging as particles from nutrients and growing medium may accumulate and block the dripper.

  7. APPA’s method is what we like to call the spray method. It follows a similar methodology as the three previously discussed methods and is optimised for home use. APPA has a tank to hold the nutrient solution, a container to house the plants’ roots, and a pump to deliver nutrients through a specially designed nozzle directly to the growing medium. We designed APPA to be as user-friendly, low-maintenance, efficient, and robust as possible. Both the ebb and flow and the nutrient film method have to use their pumps for long periods, resulting in higher cost and making them too noisy for homes. Therefore, APPA resembles a drip system, but instead of drippers, it uses a spray nozzle. This eliminates unnecessary tubing and the drippers, decreasing the need for maintenance and the risk of clogging. By design, the spray system not only waters the roots, but also keeps the growing medium wet, so that cultivation from seed is possible. A small drain hole retains some water at the bottom of the root container, increasing robustness against power outages. When the nutrient solution runs low, APPA will ask you to refill it.

    Pros: APPA combines all the best aspects of the ebb and flow, the nutrient film, and the drip method. The spray intervals and durations are customisable and can be set separately for day time (grow lights on) and night time (grow lights off). Combined with APPA’s specialised grow lights, it cultivates fast-growing, healthy, and delicious plants.

    To find out more about the importance of grow lights and how they can influence the plants’ growth, looks, and even taste, stay tuned!

    Cons: As a tabletop home system, APPA is relatively small. While perfectly suited for herbs and small bushy plants like our Cherry tomato and our Chilli "Apache", it will not fit large crops. However, we are working on APPA’s big brother, with four times the growing area and 40cm growing height.

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