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The “Ultimate” growing system is a significant shift from the traditional media grow bed commonly used in backyard aquaponics systems.

The basic flood and drain media grow bed is limited in terms of the plants that it can support and (subject to the media used) it can be expensive to build.

While they both have their origins in constructed wetlands, the “Ultimate” addresses the principal limitations of the flood and drain media grow bed in that it can support any plant and, since it can utilise the same materials used in soil-based gardens, it can be considerably less expensive to build.

While it is a horizontal, sub-surface, continuous flow constructed wetland, the “Ultimate” also draws its design influence from:

  • Sheet mulching
  • Wicking beds
  • Square foot gardens (SFG)

The simplest way to describe an “Ultimate grow bed is to imagine a subsurface continuous flow grow bed on which we place a soil-based garden fitted with a planting grid.  You can also think of it as a wicking bed through which water continuously flows.

Sheet Mulching

The inclusion of the sheet mulching in the “Ultimate” design acknowledges that fertility is at the heart of any effective soil-based garden – and sheet mulching is a very effective way to build and maintain soil fertility.

As the name suggests, this method uses mulch to build structure into the soil to enhance its water-holding capacity, to regulate the temperature of the plant root zone and to suppress weeds.

Among the “no dig” genre of gardening systems, sheet mulching eliminates the need to dig the soil – so it’s perfect for lazy gardeners or those with physical limitations.  It has also become popular for its ability to allow inexperienced gardeners to achieve good results with little more than suitable mulch and a seasonal planting guide.

Sheet Mulch Gardens

Sheet mulching – my first attempt to integrate fish production with soil-based gardening.

For “Ultimate” grow bed purposes, a sheet mulch bed comprises a layer (100mm thick) of shredded newspaper or cardboard (my preference).  This layer assists the “wicking” effect – drawing moisture up from the gravel below – and, as it rots down, it underpins the fertility of the bed.  It also helps to prevent the growing mix from silting up the continuous flow gravel bed below.

The next layer (about 150mm thick) is a mix of equal quantities of garden loam, good compost  and coco coir in equal quantities.  This is the layer into which the seedlings (or seeds) are planted.

The final layer, and an important part of the process, is a layer of mulch.  You can use pretty much any clean shredded material including sugar cane residues, lucerne mulch, pea hay or shredded garden waste.  We’ve begun to use shredded bamboo trimmings and mango tree leaves.

While we’ve successfully used sheet mulching for over twenty years, it still suffers from  reliance on humans for water.  We were never quite sure whether we were over-watering or under-watering and plants tend not to do well in either extreme.

That’s where wicking beds shine.

Wicking Beds and Subsurface Continuous Flow

The advent of wicking beds (self-watering pots on a garden-scale) removed the uncertainty around watering in that the plants help themselves to as much water as they need.  The incorporation of a water reservoir beneath the bed also extended the often tedious daily watering routine.

Grow Bed 2

Sub-surface continuous flow media grow beds – none of the fuss of flood and drain.

Wicking beds can be problematic if organic matter makes its way into the water reservoir – particularly if it is a volatile substance like fertiliser, plant matter or animal manure.  The development of anaerobic conditions will turn a productive garden into a septic system very quickly.

Setting a wicking bed up so that there is always a continuous flow of well-oxygenated water below the bed resolves this problem.

Square Foot Gardening

Mel Bartholomew, the architect of SFG, claims that a 4′ x 4” square foot bed is the practical equivalent of a 10′ x 8′ traditional garden.  At the heart of that claim is an innovative planting grid that maximises the number of plants that can be grown.

SFG encourages planting in squares rather than rows.  Different plants are sown in each square at the rate of 1, 4, 9 or 16 plants per square foot (depending on the plant).

SFG3

A square foot garden – with its characteristic planting grid.

While Bartholomew recommends a growing mix that comprises compost, peat moss and coarse vermiculite, we substituted coco coir for the peat moss – on sustainability grounds.

For the purposes of “Ultimate grow beds, I also prefer the use of garden loam in place of the vermiculite.   Based on our experience of wicking beds, it doesn’t appear to be necessary and the use of garden loam (a mix of sand and clay) gets us closer to the ideal of a soil-based garden.

These beds will continue to improve over time.  Each successive mulching will improve the soil structure.

OK……let’s summarise.

“Ultimate” grow beds:

  • are less expensive for a given area than media grow beds that utilise clay pebbles.
  • can accommodate any plant.
  • don’t suffer from the vagaries of nutrient fluctuation.  The nutrients in the water supplement the inbuilt fertility of the soil.
  • get consistent watering.
  • are prevented from becoming anaerobic by a continuous flow of oxygenated water below the soil layer.
  • offer better protection from extremes of hot or cold – due to the use of mulch.

If “Ultimate” growing beds are great vessels for growing plants, a recirculating aquaculture system is the ideal engine to power them.  Having said that, they are not dependent on aquaculture or aquaponics systems.

Such is their versatility that they can be run as organic hydroponics systems.  They can also be set up for vermiponics.

The closest thing to the “Ultimate” grow bed, of which we’re aware, is the Earthan Bed……but there is one important difference.

In the Earthan bed, the water is recirculated through two distinct loops – with a common connection to the aquaculture system through the filtration system.  The architect of the Earthan beds states that this direct connection has produced no water quality issues.

I’m of the view that, while we’re happy to use the nutrient-rich water from our fish tanks, there should be no movement of water from the “Ultimate” bed back to the aquaculture/aquaponics system.   I’ve taken this approach because:

  • By opening the loop between the fish and plants, we can practice the water replacement that optimises our water quality while still preserving the water efficiency of  the “Ultimate” grow bed.
  • We can integrate other nutrient recovery strategies into our plant growing system – like brewed compost tea.
  • We can isolate both systems from each other…..and run each system indefinitely if our circumstances require it.
  • We can use organic pesticides if we choose without harming our fish and, in the unlikely event of a problem with our fish, we can use salt without causing detriment to our plants.

In the absence of any demonstrable gain, I don’t think the direct connection between  fish and soil-based gardens is worth the risk (however small) of compromising water quality…….and, as I’ve demonstrated, there are advantages for us in not doing so.

In the next post, I’ll detail the construction and operation of the “Ultimate” growing system

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