How to choose the proper growing media
Welcome, today we will go over how to select the correct grow media for your aquaponic system. Grow media comes in several shapes and sizes made with various materials with numerous different properties; often several types are blended. The final product must provide four characteristics to ensure proper growth.
In aquaponic and hydroponic operations the nutrient solution provides nutrient, water, and to some degree oxygen to the plants, though the medium used can significantly affect the overall health of your plant.
The choice of medium is often determined by its availability, cost, quality, and the type of hydroponic growing method used. Several examples of commonly used substrates include Coco-Coir, Rockwool, Peat moss, Light Expanded Agricultural Clay (LECA), Gravel, Pumice, Rice Hulls, Foam, and Polyethylene Filter Mats.
When choosing your media, you should consider the medium’s moisture retention, oxygen retention, drainage, rigidity, and abrasiveness. The media should be inert and unable to affect your culture water; therefore media from a limestone source or media with a high content of calcium carbonate (CaCO3), should be avoided as these will slowly release carbonates into your system and raise pH and lock-out other nutrients. Other mediums like Sawdust and Coco-Coir naturally have high levels of sodium and must be washed before use to ensure proper plant growth.
To help we have created these easy comparison charts of commonly used mediums.
Germination is greatly affected by the temperature, humidity/moisture, and any scarification required by the plant before seeding. Best results are achieved by sowing seeds in Rockwool, coco-coir, peat moss, or some mix outside of your aquaponic system. Direct sowing into your system can be done through control of environmental controls is limited, and germination rates will be decreased. To make life easier manufacturers have created premade grow plugs which seeds can be planted. For the cost, quality, and simplicity we recommend plugs that are a coco-coir peat moss blend; these generally come in 128-plugs per 10″ x 22″ tray. Rockwool is packaged in slabs with small blocks that can be removed. Soak the medium before sowing seeds as this will increase germination. Also, it is recommended to use a humidity dome as newly sprouted plants must absorb water from the air until its roots have had time to develop.
Once the first true leaves have developed the seedlings can be transplanted into your primary system. Generally, media beds are a minimum of 12″ deep this allows for healthy root development, water height should be 2″ below the surface of the media to prevent algae and fungus development.
While many substrates work, some require more work than others; for its benefits and simplicity to working with over other mediums, LECA (Grow !t) is preferred for growers of all expertise levels media based systems. If LECA is not an option for you, then there are alternatives, and you can use the charts above to determine the next best media for your location and system.
Sterilization of Medium
Over time – regardless of the medium you use – there is the potential for soil-borne pathogens to develop. In Aquaponic system vs. Hydroponic systems, we promote a healthy biome which tends to limit the number of pathogenic organisms, though it is still possible to have outbreaks of various pathogenic microorganisms such as Pythium, Fusarium, and Verticillium. To help prevent outbreaks, sterilization of the media before it entering the system is recommended especially in commercial operations. Additions of various probiotics into the system can also help prevent outbreaks. If an outbreak occurs the most economical way to sterilize media is with steam. If your system is heated with a water boiler then a steam converter attachment can be used to steam your media; typically this is done at 180 oF.
Another more straightforward method for small scale growers is the use of bleach at a concentration of 10,000 ppm of available chlorine can be diluted in the wash water for the media. The medium should soak for half an hour to kill any unwanted pathogens; this can be done in your system water if there are no fish in the water or if the hydroponic system is decoupled from your Aquaculture system.