Aquaponics Growing Medium

Last Updated on January 23, 2022 by Fabiola L.

Aquaponics growing mediums use media beds filled with medium to hold the plant root system and allow for nitrifying bacteria to grow. Grow beds are a common hydroponic growing technique for aquaponics. Some practitioners think of grow beds as a mechanical filter to trap the fish waste. Although this will cause buildup of waste and anaerobic bacterial growth in the grow bed. Before considering the grow bed, make sure you have a mechanical filter in place to remove the waste from water. However, grow beds will provide housing for the nitrifying bacteria and serves as a biofilter for your aquaponics system.

Aquaponics Growing Medium For Grow Beds Should Have Inert pH and Will Not Decompose

Personally, I prefer not to use grow beds for aquaponics, but it is a great system for hobbyists and small-scale systems. According to Dr. Wilson Lennard, aquaponics grow media serves as a biofilter, a mechanical filter, a grow box for plants and a site for mineralization. This allows for grow beds to serve multiple purposes removing the need for complex equipment. This works best for hobbyist scales and low-density aquaculture setups. In larger setups, buildup of solids will occur and lead to nutrient imbalance. Good growing medium for aquaponics allows roots and air to pass through the media without damaging the roots. Water retention will not improve aquaponics systems because water is constantly running throughout the system. In deciding what medium to use, consider the cost, weight, porosity, and composition of the material.

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Gravel For Aquaponics Growing Medium Is A Low-Cost Alternative But Could Damage Sensitive Roots

Some small-scale hobbyists often use gravel as a growing medium. Gravel differs in sizes but most have sharp edges that could damage your plant’s root systems. The weight also sets back the potential of gravel as a growing medium. Although plants can still grow with gravel as it provides good root support. Gravel will also have good drainage and aeration between the root systems since air can pass freely between each piece. Drainage prevents water logging in your grow bed. Since gravel has edges and crevices, nitrifying bacteria and mycorrhiza can grow on its surface. This will improve the overall nitrogen cycle in your system, improving plant growth. Before using gravel for your system, make sure to wash thoroughly until the water that passes through is clear. Gravel contains a lot of fine particles from its production that could potentially harm your fish and make your water cloudy. It is also advised to clean out gravel beds in case there is a buildup of fish waste.

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River Pebbles Provide Smooth Surfaces Which Don’t Damage The Roots

Pebbles are another low-cost alternative for aquaponics growing medium. Their smooth surfaces won’t damage the plant’s root system. River pebbles are heavy which will make it difficult to carry and will require substantial support for the grow bed. Gravel also provides good drainage and aeration for plant roots. Like for gravel, this will prevent waterlogging for plants. The smooth surface of pebbles do not give good root support since the roots are not held in place. When transplanting into pebbles in your grow bed, place the plant root system at a depth that covers the root plug and place some pebbles to support the stem. Be careful not to place too much pressure on the roots as well. Also, avoid using pebbles and gravel that come from limestone as this may disrupt the pH balance of your system.

Sand Used As Aquaponics Growing Medium Is Low Cost and Allow For Good Drainage and Aeration

Using sand as an aquaponics growing medium requires proper system design to prevent the sand from flowing to other components. Sand is a low-cost alternative which is accessible to everyone. Sand, just like gravel and pebbles, does not retain water which allows for better drainage. Air will be able to pass through between the sand particles, letting the root system of the plant breathe. Sand will provide a better environment for nitrifying bacteria than gravel and pebbles because of the surface area available. Each sand particle is also light enough for roots to easily run through. Although additional support might be needed for supporting the plant to stay upright.

Hydrotons Or Expanded Clay Pellets Allow For Air and Water To Pass Through Inside The Pellets

Hydrotons are the best choice for grow boxes due to the availability and characteristics of the clay pellets. Expanded clay pellets are porous which increase the surface area of contact with water. Increased surface area lets nitrogen-fixing bacteria convert the solid fish waste in the water into nitrates for the plant. Before using hydrotons, be sure to clean thoroughly since there are a lot of clay particles from production of hydrotons.

 Hydrotons Or Expanded Clay Pellets

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Lava Rocks As A Medium Has High Surface Area and Good Drainage

Like hydrotons, lava rocks provide high surface area due to the small crevices of each small particle. Lava rocks will come in different grain sizes. Choose the larger grain sizes for aquaponics as they do not float as much as the fine particles. Coarse lava rocks will also give better drainage than small particles. In choosing lava rocks, be sure that they are pH neutral and free of floating sediments.

Avoid Using Coco Coir, Coco Peat, and Limestone As Aquaponics Growing Mediums

Organic materials decompose easily in aquaponics systems and will cause bacterial growth. Decomposing organic matter adds to the biological oxygen demand of your water due to the bacterial processes. These materials weigh light enough to float in water. This causes a problem in the material flowing to other components of your aquaponics system. Organic materials retain water well which might cause waterlogging for your plants due to the constant flow of water into your system, even in an ebb and flow. These materials are commonly used for hydroponic drip systems but do not work well in an aquaponics system which floods the grow bed.

Grow beds work well for small-scale systems that do not produce a lot of fish waste. In deciding your aquaponics growing medium, take note of floating sediments and changes in acidity. Using a grow bed for your aquaponics system provides a lot of benefits for small-scale systems. In large-scale systems, there will be difficulty in cleaning and solids removal from the system. The breaking down of solid fish waste will not be able to keep up with the amount coming into the system.

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