Design 2

Design

To be clear, we don’t actually design a sandgarden…that’s already happened. The critical success factors that we identified in the last section are the sandgarden design.

Every sandgarden is identical to another in terms of its basic component parts and operating method – from a square meter to 10,000 square meters. Designing a sandgarden is actually more about choosing a layout…and then applying the layout at the scale you want/need.

Modularity

My personal commitment to the notion that small is beautiful reflects itself in every aspect of what I do…and that means I’m a fan of modularisation.  

I like to build a small prototype – ensure that it works – and then replicate it. 

I’d generally rather have several discrete units than one large one because:

• It’s less risky.  If a module fails, the problem (and its consequences) is limited to the module.  But if a single large unit fails it’s likely to be catastrophic.
• I have a Bootstrapper mentality when it comes to business and that means that I won’t borrow money to fund an enterprise. Your sandgarden can be expanded commensurate with your resources – using the outcomes from existing modules to fund future ones.
• In a sandgardening context, having discrete modules enables cohort production – where you plant and harvest each module at pre-determined intervals…and your overall food production increases with each freshly commissioned module.
• Smaller sandgardens are also more cost-effective for DIY builders.

We’ve provided three system designs – each of them an authentic sandgarden – with the only difference being their size.

It all comes down to your needs, preferences and resources.

Before we dive into that, however, there are a few things to bear in mind as we proceed.

Things to Consider

The following factors are applicable to any type of gardening – and are not meant to overwhelm you.  They’re simply a handful of things to keep in the back of your mind as you set out to design your sandgarden.

 Location

In setting up a garden, it’s vital that the plants receive sufficient light, so ensure that your proposed space receives sunlight of adequate intensity and duration. Plants cannot receive too much natural light.

While sandgardening is very well suited to off-grid operation, most people will opt to use 120/240-volt pumps and timers (at least initially) so access to electricity is important, too. In impoverished remote locations, manual (non-electric) operation is also feasible.

Water is heavy, so we don’t want to carry too much of it.  Ensure that your proposed build site has convenient access to suitable water.

If you have experienced floods on your property – or anticipate them – think about where your sandgarden is going to be most secure.

 Sustainability

Herbicides, pesticides and other industrial chemicals are not organic and have no place near a sandgarden.  The planet is well overdue for a respite from poisoning, so cut it a break and use materials with the lowest possible environmental impact – or those that can, at least, be fully recycled.

 Durability

Your choice of system components should take their lifespan into account. Budget constraints aside, there is no practical substitute for quality. While best-quality components are typically more costly, they are invariably the most cost-effective and reliable choice over the long term

Aesthetics

Whether you get to engage in food production may require that you satisfy your partner that you are not going to create an eyesore in your backyard.

Similarly, your neighbours may begin to take an unhealthy interest in your system if they perceive that their property values are negatively impacted by your activities.

You may argue that what you do in your own backyard is your business, but local government authorities will take a different view if they start receiving complaints from disaffected neighbours.

A neat and tidy system is also easier to operate and keep clean.

Nuisance Potential

The sound of running water might be music to your ears, but could well drive a neighbouring shift worker to distraction.  Locating your system out of the hearing range or neighbours will avoid this issue.

Nothing will bring the wrath of the local health inspector down on your head faster than something that stinks or attracts vermin.  Managing your system in a hygienic state is essential. Fortunately, this is easy with a sandgarden.

To repeat, don’t let these considerations distract you from building a sandgarden.  They apply to all forms of gardening, so just keep them in the back of your mind as we get on with the process of designing and building your first sandgarden.

Layout Options

Gravity is Good!

The simplest approach is to position the sand biofilter so that it drains directly back into the water tank. Not only is this arrangement simple to execute, but it only requires a single water pump. With next to no plumbing, it has minimal points of failure.

The pump, located in the water tank, moves water up to the sand bed.  The water then percolates down through the sand and drains back into the water tank.

The advantages of this arrangement are that it’s easy to understand – and similarly easy to build and operate.

Having the pump located in the water tank affords its own advantage in that the solids are macerated as they pass through the pump, which causes them to be more evenly distributed throughout the furrows.

To be clear, this is the preferred layout method wherever possible.

That said, there are those situations where it may not be desirable (or even possible) to put your tanks in-ground.  

The good news is that water tanks can be located on or above ground – and there are a couple of ways that this can happen.

1. Sump Tank System
2. Constant height – one pump (CHOP)

Sump Tank System

With this option, a pump is located in the water tank.  The pumping cycle is initiated by a digital timer, which causes water to be pumped from the water tank to the sand beds.  The water percolates down through the sand, exits the sand bed and drains into a small sump tank.

A sump pump is located in the sump tank.   A float switch triggers the sump pump once the water level reaches a certain level and the water is pumped back to the water tank.

The benefits of this arrangement are that water tanks can be located above ground and only a small sump tank is required.

Note:  One of the prospective concerns is the energy use involved in using two pumps, but neither pump is activated for more than 2 hours per day.

The disadvantage of the method is that, in the event that the sump pump should fail, the pump in the water tank could (following several pumping cycles) pump the water tank dry.  This risk could be mitigated by installing a magnetic float switch in the sump tank so that, once it fills beyond a certain point, it bypasses the digital timer that triggers the operation of the water tank pump.

Constant Height – One Pump (CHOP)

If, for whatever reason, you would prefer to use just one pump, then the CHOP option is for you.

With the CHOP layout, the water is pumped from the sump tank up to the water tank.  This inflow displaces water, forcing it up the solids lifting outlet so that it exits the water tank and out into the sand beds.  It then percolates down through the sand and then drains back into the sump tank.

The benefit of the CHOP approach is that only one pump is required and the prospective point of failure (posed by the sump pump) is eliminated.

The downside is that the sump tank has to be large enough to contain any water that drains back to the sand beds after the pump cycle is completed.

Another possible disadvantage (yet to be confirmed) is that solid wastes are delivered to the sand beds relatively intact – with the possibility that they may build up in that part of the furrow which is closest to the inflow point.

It remains to be seen whether this is an issue in practice and may also vary by the fish species in use.   The composition of fish feces varies from one species to another.  Tilapia, for example, excrete long fecal strands while the output of others is shorter or more soluble.

Having determined what layout method you’ll use, it’s time to take a look at how to set up sand biofilters.

Sand Biofilter Positioning

You have three options when it comes to how you build sand biofilters.  

You can put them in-ground, on-ground or above ground.

It should come as no surprise to learn that we favour the IN-ground option.

For as much as you’ve heard me speak about sandgardening being productive, resilient and sustainable, the in-ground option is THE MOST PRODUCTIVE, RESILIENT AND SUSTAINABLE of the sandgardens. It’s also the easiest and most cost-effective way to build a sandgarden.

Having revealed the best option, however, it has to be acknowledged that there are situations where the in-ground approach won’t work.

Are you in an area prone to flooding or torrential rains?   Is your only available space under concrete, asphalt or paving?   Would your spine and back muscles prefer that your sand beds be at waist height?

Regardless of the motivation, you can continue to build a sandgarden but instead of making ‘cut and fill’ containments in the ground, you make a box (tank) and a tray (sand bed) out of whatever is available to you – on-ground or above ground. 

The only difference between the in-ground approach…and its on-ground and above-ground variants…is more work and the added cost of the containments for the fish and the plants.

The added construction cost aside, it’s still a sandgarden in terms of its footprint and capabilities.  

In some situations, the added cost may even be reconciled by added convenience and/or operator comfort.  For example, sand beds might be raised above the ground to permit wheelchair access.

Now, that we’ve determined what layout we need, it’s time to look at some sandgarden designs.

Square Metre, Starter or Carpark Model?

Since all sandgardens operate in essentially the same way, our ‘designs’ – are differentiated from each other by size.

• Square Metre
• Starter
• Carpark

Square Metre Sandgarden

A square metre is a space – a footprint – upon which many horticultural metrics are based. For example, we think in terms of so many plants per square metre…and later we’ll be talking about feed rates per square metre. The point is that it’s a useful size upon which to base our smallest design.

The Square Metre Sandgarden is a small demonstration unit that features a one-metre by one-metre sand biofilter with a depth of around 330mm…and a total footprint of two square meters…one for the sand biofilter and one for the fish tank.  

That said, this is not a toy. It’s a fully functional square meter of sandgardening territory – intended to replicate the behaviour of larger units, It’s a demonstration unit, a learning aid, and a seedling propagator. The effort spent in building the Square Metre Sandgarden will repay itself many times over.

It’s also very convenient when it comes to reporting outcomes. With an eye on the future, we’ll be encouraging square-metre system builders to join us to compare their systems and results.

Basic Shopping List

• Sand biofilters – 3 linear metres of 2-metre-wide liner for the sand bed.
• A water pump – you’ll need the smallest submersible pond pump that you can find with a 19 mm (3/4″) outlet. Anything smaller than this is a maintenance nightmare. It will be capable of moving more water than we need, but we can throttle the outflow without issue. In any case, the extra capacity will allow for expansion if you decide you want to build more square meter units in the near future.
• A digital recycling timer – programmable for short intervals (one minute or less) at least eight times in any 24-hour period.
• 3 meters of 20 mm (3/4″) plastic potable water hose – and the necessary fitting to connect it to the water pump.
• 330 litres of silica quartz sand.

Note: I’ve deliberately avoided mentioning brand names since they will vary between locations.

System Productivity

The question of what can be grown in a single square metre is an interesting one. Theoretically, based on the production of the carpark model, it should be capable of producing up to 80 kg/year. We really have no idea of what the upper limits look like at this stage. In any case, we can think of it as a benchmark.

Now, if you decided to build your system over time…for resource reasons…you could simply continue replicating square-metre biofilters…one at a time…as resources permit. When you have six such units in play, you would have the equivalent of a Starter Sandgarden – 6 square metres. 

Starter Sandgarden

If you require no more convincing that iAVs is able to provide you with clean, fresh organic food, then you might consider a Starter sandgarden for your first build.

Basic Shopping List

• Liners – 8 lineal metres of 2-metre-wide liner for the sand bed…and a 4 m by 4 m liner for the fish tank.
• A water pump – with a capacity of 1200 litres per hour at a developed head height of 1.0 – to 1.5 metres.
• A digital recycling timer – programmable for short intervals (one minute or less) at least eight times in any 24-hour period.
• 8 meters of 20 mm plastic potable water hose – and the necessary fitting to connect it to the water pump.
• 2 cubic metres of washed and graded silica quartz sand.

System Size and Productive Capacity

With these few components, we’ll build a sandgarden with a 1,000-litre fish tank – and six square meters of sand bed – containing two cubic metres of sand – weighing about three metric tons.  It will occupy a total footprint of around 8 square metres.

Managed according to iAVs guidelines, a system of this size will enable you to grow 350 kg+ of fresh fruit and vegetables and 50 kg+ of freshwater fish per year – a nutritious diet for a single person.

Carpark Sandgarden

This was the American ‘carpark’ model – where big ‘gas guzzlers’ are the norm. Our version will reflect the international move toward smaller vehicles.

The new Carpark sandgarden comprises 18 square metres of growing space and three cubic metres of water tank capacity.

It will feature a 3,000-litre fish tank – and 18 square metress of sand bed – containing six cubic metres of sand – weighing about nine metric tons.  It will occupy a total footprint of around 28 square metres.

Basic Shopping List

• Sand biofilters – 25 linear meters of 2-metre-wide liner for the sand bed – assume the use of rows.
• A water pump – a pump with a capacity of around 3000 litres per hour at an operating head of 1.0 – 1.5m is required.
• A digital recycling timer – programmable for short intervals (one minute or less) at least eight times in any 24-hour period.
• 3 meters of 25 mm (1″) plastic potable water hose – and the necessary fitting to connect it to the water pump.
• 330 litres of silica quartz sand.

The basic shopping list is also impacted by how you set up your sand biofilters as rows – or as one large one – and how you water and drain the biofilters. The further you venture from the in-ground version, the greater the capital requirement.

System Size and Productive Capacity

Built and operated within iAVs specifications, the Carpark iAVs will produce not less than 1400 kg of clean fresh organic fruit and vegetables – and 200 kg of fish – per year.

Which One?

All three of the system layouts that we have presented are authentic sandgardens. It all comes down to your needs, preferences and resources.

It would be better to build the square-metre unit if it means you can start sooner. Like now! 

Any inhibition on your part will quickly give way to excitement when you experience the method directly…and the resources that you invest in a square-metre iAVs will provide a dividend very quickly. Not only will you be experiencing sandgardening at a fully-functional and practical level, but it will make a perfect seedling propagator when you elect to scale up to larger units.

Do you want to grow food for yourself? For others? Commercially?

Key Points

• Each of the three systems operates in the same way. The only thing that changes is the variable cost of the components and operating expenses – from one square meter – to 6 m² – to 18 m² – to a million square meters. 
• Each of the three systems exhibits a 1:2 ratio of fish tank volume to sand biofilter volume. A Square Metre Sandgarden utilizes 170 litres of water and 330 litres of sand. A Starter iAVs utilizes 1000 litres of water and 2 cubic metres of sand. A Carpark model utilizes 3000 litres of water and 6 cubic metres of sand.

Key Points

• Embrace modularity – grow as you learn; learn as you grow!
• Utilise gravity – have the sand biofilters drain directly into the fish tank wherever possible.
• Reconcile your proposed sandgarden with the available space – and your neighbours.

Task List

• Choose which of the three systems will be your first build.
• Develop a materials list – based on what is available in your location.
• Google to determine where your components can be sourced.
• Calculate the cost of your proposed system. You need to know how much you’ve invested if you’re going to know your return on investment.

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