A lot of the care you put into your aquaponics system revolves around the fish tank, but a good grow bed is just as important for cultivating reliable crops. There are a number of options available to you for your aquaponic grow bed. There are costs and benefits to each, and one may be better for your set-up than another, so learn as much as you can about these options before you make a choice on which to use.
Tip: Do not use soil, peat moss, or wood chips for planting, as it will decompose and clog the system.
A type of clay pellet that expands when wet, hydroton forms a dense soil-like layer roots can easily grow into. These pebbles are particularly smooth, making them easy on sensitive roots. This substance is also pH neutral, meaning that no acid will build up in your water supply, adversely affecting plant growth. It drains freely too, aiding in the oxygenation of roots.
Tip: Do not use limestone as it will push the pH above healthy limits.
A natural mineral that is commercially mined and converted into a gravel form, vermiculite expands with the addition of heat. While your grow medium will be inevitably wet, the heat level varies according to your needs and desires, allowing you substantially more control over its expansion. However, natural vermiculite can contain asbestos, creating a potential health hazard. If you use this substance, make sure to obtain it from an industry-regulated source so its safety can be verified.
Epoxy-coated aquarium gravel is an affordable and simple solution for an aquaponic system. While it does not have the oxygenating properties of hydroton or the expanding properties of vermiculite, aquarium gravel is generally a safe solution for a standard set-up. If, like many aquaponic enthusiasts, you are interested in using recycled materials to make your system especially eco-friendly, you may opt for aquarium gravel because its wide availability means it is easy to obtain used from aquarium owners. While it's not your primary concern, it is worth noting that the colorful pieces in aquarium gravel can make for some artistically engaging aquaponic set-ups.
While not as nice or as aesthetically pleasing as other alternatives, drainage gravel gets the job done and is relatively inexpensive. In addition, its higher density enables drainage gravel to support taller plants that clay pebbles simply cannot. Aquaponics gardeners who cultivate corn and other stalked plants prefer the density of this material to clay alternatives.
Which Medium Is Right for You?
How the ups and downs of each medium equal out for you depends significantly upon the environment in which you are growing. As is often the case with aquaponics, a little trial and error is necessary before you strike an ideal balance. If you can, buy a few different grow media and try them out in separate growing tanks. Does your lettuce grown in clay look leafier than your lettuce in aquarium gravel? Then you've learned an important lesson for your future aquaponic endeavors.
Creating a Lasting Grow Bed
Fill the growing bed about a third of the way with the medium of your choice, lightly packed. With most containers, this comes out to be about 300 mm deep, but your individual experience may vary.