The most popular plant growing system (among backyard aquaponicists) is the media grow bed.
I have to say, however, that my relationship with media grow beds has been a bittersweet one.
Coupled with dedicated mechanical and biological filtration, they’ve made for a productive, resilient and versatile recirculating aquaculture system – with the added benefit of being able to produce plants.
Regrettably, I’ve also been witness to their use in a basic flood and drain context (where the media grow bed is used to perform all of the filtration functions of the aquaponics system) and the experience has been rather more problematic.
Regardless of their configuration, media grow beds are a substantial undertaking and, depending on the choice of media, they can be expensive. They are also limited in terms of the plants that can be grow in them.
Other aquaponic growing systems, like raft tanks and NFT troughs, are similarly expensive and limited.
The Quest for a Better Way
With all of this in mind, I began (several years ago) to search for cheaper and more versatile alternatives to the humble media grow bed.
I’m of the view that, not only is aquaponics not the only way to integrate fish and plants, it’s quite often not even the best way – so I’ve long been an advocate for the use of soil-based growing units in conjunction with recirculating aquaculture systems.
To that end, I’ve used:
- Raised sheet mulch beds – popularised by David Holmgren and Bill Mollison – the architects of Permaculture.
- Square Foot Gardening – the brainchild of Mel Bartholomew.
- Wicking Beds – developed by Colin Austin.
Aside from their efficiency of water use, each of these gardening strategies provided me with a single significant advantage.
Raised sheet mulch beds, for example, build soil fertility like nothing I’ve used before.
The key idea behind square food gardening is the use of a planting grid that optimises the use of growing space.
Wicking beds help to overcome the single biggest issue around gardens – watering. Soil-based gardens are invariably under-watered or over-watered. Wicking beds enable the plants to regulate water use and, in so doing, extend the intervals between watering.
Which one should we choose?
The short answer is…….all of them – or (more specifically) a combination of all of them.
While each method is a stand-alone strategy, the central benefit of each can be leveraged into a single uber gardening system…..the raised – sheet mulch – square foot – wicking bed.
We built a small prototype and, while it worked well enough, we encountered a problem with the wicking bed aspect of the system.
Organic matter made its way into the water reservoir of the bed and and things quickly turned anaerobic – and started to stink.
I attempted to fix the problem by placing an air stone into the reservoir but it met with limited success.
I then created an external water reservoir by placing a sump tank underneath the bed. A timer-controlled submersible pump moved water from the sump tank into the grow bed – from the bottom – in the same manner as a hydroponic ebb and flow system.
This was a distinct improvement but it was clumsy and, because it the water was transporting volatile organic matter into the sump tank, it still produced a foul smelling brew.
A couple of air stones resolved the bad odour but I still felt there was scope for further improvement – and then other priorities forced my attention elsewhere.
As it turned out, the final piece of my grow bed puzzle presented itself several months later.
In the meantime, one of my other ongoing projects – the creation of a grey water treatment system for our micro-farm – saw me researching the use of constructed wetlands to the remove contaminants in domestic grey water.
One particular type – the horizontal, sub-surface, continuous flow constructed wetland – caught my eye. It comprised a gravel bed upon which sand or soil is placed. Plants are grown in the soil.
Effluent flows through the gravel layer (immediately below the soil/sand layer) and wicks up to the roots of the plants. The aerobic environment beneath the soil/sand layer facilitates the take up of nitrogen and phosphates from the effluent.
I read the name a second time and I noticed the term “continuous flow”….
…..and then the penny dropped
I realised that this wetland was a scaled-up cross between a continuous flow media grow bed and a wicking bed.
It occurred to me that, if this hybrid was capable of removing contaminants from domestic effluent, there was no reason why – on a smaller scale – it would not do the same thing with the nutrient-rich effluent from a fish tank.
A few days later, in what can only be described as a freakish coincidence, a new member on the APHQ discussion forum announced…..
“One (grow bed) is planned to contain only hydroton, while the other will have a soil mix (soil/vermiculite/compost) over a few inches of hydroton; both will be sub-surface, continuous flow.”
The same post contained a reference to Earthan beds…..another example of the integration of recirculating aquaculture and a soil-based gardening system.
Eventually, we established that Earthan beds were also a grow bed-scale variation on the horizontal, sub-surface, continuous flow constructed wetland.
While I had travelled a different route, this discovery confirmed that the combination of continuous flow grow beds – and my preference for soil-based gardening systems – was not only viable, but offered advantages over any other growing system that I had seen previously.
While I’m happy to acknowledge that the horizontal, sub-surface, continuous flow constructed wetland is the precursor to my efforts, it’s full title is a real mouthful. That, coupled with the other systems that have influenced it……and the advantages that it offers…..encouraged me to re-badge it with the much shorter and more optimistic-sounding name……..the “Ultimate” grow bed.
In the coming days, I’ll detail each of the component systems – and how they contribute to the the “Ultimate” aquaponics growing system.