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Media-filled beds are the most popular type of small-scale aquaponics system. This design generally has low initial costs and is space-efficient. Because of their simplicity, media beds are easily the best setup recommended for beginners. If you are planning to have a media grow bed, one of the things you need to consider is the depth. But what is the best bed depth for aquaponics?
Getting the right depth for your media bed is essential to the system’s success, as it controls the amount of space that the plant roots can occupy. When choosing the best bed depth, you should consider the following factors:
- Choice of shallow vs. deep beds
- The type of plants you intend to grow
- Your budget
In this article, we will discuss the different zones in a grow bed, the recommended bed depth for aquaponics, and other factors.
Understanding Aquaponic Media Bed Zones
In a media bed design, three zones serve an essential purpose in your aquaponics system. These zones are the dry zone, root zone, and the mineralization zone.
Zone 1 – Dry Zone
Within the first five inches of your grow bed lies the dry zone. This area needs to be maintained dry as it helps prevent evaporation. At the same time, this area discourages the growth of algae on the media surface and the development of other moisture-related diseases such as collar rot.
Zone 2 – Root Zone
The root zone is where plant activity is most pronounced. This area is between six to eight inches deep into your grow bed and is regularly flooded and drained. As the flood and drain cycle starts, the incoming water spreads out nutrients, moisture, and fish waste around the area. Worms are placed here to break down the solid waste and eat up the decaying matter, like dead leaves or roots.
Zone 3 – Mineralization Zone
The remaining 2-inch bottom part of your grow bed is the solid waste collection and mineralization zone. Fish waste and worm castings accumulate in this part of the grow bed.
With the help of heterotrophic bacteria and other beneficial microorganisms, waste particles are further broken down into smaller molecules that can be absorbed by plants.
How Deep Should Your Aquaponics Media Bed Be?
To decide on the best depth for your grow bed, you have to factor in the plants you plan to grow and your budget. Will you be growing solely leafy greens, or do you wish to plant different types of crops? Will you have only shallow beds, or do you need to have a deep bed? In this section, we will address each of these factors.
Shallow vs. Deep Aquaponics Media Beds
With the different zones that make up the small artificial ecosystem, experts recommend a standard media bed depth of 12 inches. Most experts agree that such a depth should be enough to keep your system working.
With this depth, the plants’ root systems will be well-supported. Anything more than that is often unnecessary and will be a waste of resources. Not to mention, it will become more challenging to maintain as the bed becomes heavier and more thirsty for water.
However, a deep grow bed is more expensive than a shallow bed because you need to fill in more of your choice of media. Also, you will have to think about the added cost to support all the weight of a deep grow media bed and the total amount of water needed in the system to irrigate at such depth.
As a result, some aquaponic practitioners choose to grow plants in a shallow bed and have done so with success. Still, it would help if you didn’t ignore the possible limitations of having a shallow media bed.
Limitations of Shallow Grow Beds
While it is acceptable to have a shallow depth for your grow bed, note that there are certain limitations to this option. When you have a shallow bed, you don’t have a lot of plant options to grow.
Shallow beds are best suited for plants that don’t have invasive root systems or roots that grow deep. This type of bed is generally for short-lived plants. Examples of these plants are lettuce and other leafy greens.
Another limitation of growing in shallow beds is the presence of “dead zones,” which requires regular cleaning of your media bed. Usually, in a 12-inch deep media bed, dead zones are absent since the perfect layering that exists encourages the growth of beneficial microorganisms that will do the cleaning for you.
Media Beds for Best Plant Growth
Whether you plan to have a shallow or deep media bed, it’s a good idea to be familiar with the root systems of your chosen crops. Shallow-rooted plants can be an economical choice if you plan to have lettuce, members of the cruciferous veggies (broccoli, cabbage) and herbs only.
On the other hand, plants that grow deep, such as tomatoes or trees/shrubs like blackberries, will need deep grow beds. These plants require adequate space so as not to allow root matting to take place. A deeper bed can provide the support the plants need as they grow. Furthermore, it allows for beneficial bacteria to grow to help plants live longer.
However, if you plan to grow a variety of crops together in one media bed, it’s best to go for the 12-inch depth straight away. Shallow-rooted plants can always flourish in deep beds, but deep-rooted plants will not thrive in shallow beds.
Deciding on the best bed depth for aquaponics will depend entirely on your needs, the purpose of your system, and your overall budget. You can save on expenses by choosing a shallow bed if you intend to grow shallow-rooted plants only. However, keep in mind that you may be presented with limited options of plants you can cultivate.
Meanwhile, if you aim to grow a variety of crops with both shallow and deep-growing roots, you’re better off going for the standard, recommended depth of 12 inches. Do keep in mind that the greater the depth of the bed, the more expenses it will incur.