Wicking Soaker beds

I developed the original Gbiota beds to grow plants which act as natural pre and pro biotics by having a moist, not wet soil. It is very easy to make soil wet, just hump on the water which will breed up the harmful microbes. It is much more difficult get the soil just moist which the beneficial microbes prefer.

I developed the original system using a system of pumps, timers and drains in about 2015 when weather conditions were very dry and they worked fine. But I learned two things.

Many people do not want the bother of installing and maintaining pumps, timers and sumps.

Freak weather

Then in 2020 the weather changed dumping massive amounts of water – multiple rains of over 100mm in a few hours. It is not just the water falling on my block – it is all that water falling on blocks higher than mine which create a torrential flow over my block which the then Gbiota beds just could not handle.

The Ag pipe act as a natural drain but they can only handle so much water – no where near what we have in these monster downpours.

This is thousands of tonnes of water moving at speed across my block, working out how to grow food with these extreme weather events is one of the key challenges facing us all.

My experiments

Dimensions

My first action was to build the beds as high above the ground as possible with drainage channels down the side.

I decided to space each bed at one metre with a channel of around 200mm on each side of the bed for a flood channels and foot path.

Most plants roots (and hence the plant) will simply die if they are left submerged for any length of time (with a few exceptions like cress and mangroves. But is if I can keep the top part of the roots free from water logging those roots will survive and the plant will survive and will rapidly regrow the lower roots.

The level on my beds was already about 100mm above the parent soil so I dug down a depth of 200mm.

For this installation I made my trench 400mm wide leaving an undisturbed zone of about 200mm on each side.

I am not saying these are ideal – just what I did as my estimate of what is best – and they worked pretty good.

Setting up the bed

The diagram shows how I made the bed. In essence I simply dug a bath tub shaped trench, some 300mm deep,and 400mm wide into the parent soil.

Along the sides and ends I left the soil in place.

I filled this trench in the normal way I make Gbiota beds.

I checked the bed was level. Laid Ag pipe flat along the base then added two sight tube for filling and inspecting moisture level. Then filled with a layer of organic waste, in this case grass clipping with all the food waste I could muster. Then a layer of manure with minerals, Dolomite to reduce acidity and Bauxite (local rock dust) which adds Magnesium plus blended rock dust (Biomin) to add trace minerals.

Finally I load some top soil, seed and surface water to germinate.

Filling

I then used a hose to partially fill the highly porous centre layer. There is a bit of trial and error here, I needed to fill with enough water so it would wick out to the surrounding soaker layers.

But I did not want to overfill and be left with stagnant water sitting in the base for any length of time.

I used an auger to check the moisture levels in the soaker layer. It turned out to be pretty simple to find out just how much water to add so there was enough to wet the whole area without leaving stagnant water.

I now had to wait until most of the water was used up which is obviously highly variable depending on weather and plant types.

This is a bit more tricky as there is no magic rules to say when the moisture level has dropped enough to need refilling – it is just a question of checking the soil with the auger and watching the plants for any sign of drooping.

To breed the beneficial microbes we need the soil moist but not wet.

Plastic film or compaction

On all my previous beds I had used a plastic film to stop water leaking away. My soil is a duplex with a layer or real heavy clay underneath and a layer of silt on top.

I decided to make two experimental rows. The first row would use a plastic film.

While on the second row I compacted the soil with a sledge hammer.

Compacted trench

To be honest – now I am growing crops I cannot really tell the difference and if anything the compaction bed is growing better but there is always a degree of randomness in growing experiments.

I have no idea if compaction would work on a sandy soil – somethings in life you just have to try and see.

My trench stopped about a metre from the end of the bed – this is part of what I call the soaker zone.

I test the trench was level with water and scraped and dug until it was level (important, I think I may treat myself to a laser levelling tool).

I laid a length of Ag drainage pipe along the base of the bed and used a couple of inspections tubes at either end. These were large enough (100mm for me to put my hand down and feel the wetness of the soil – ac critical part of the experiment.

On the inlet side I did put a piece of plastic file under the inspection cum filler tube to stop the water soaking into the ground at the start – no idea whether it is necessary or not after all my banging.

I back filled with several layers, the first was organic waste – I really wanted food waste but I have found we jut do not produce enough at home and I have exhausted the friendly local restaurants – so I made do with grass clippings which are abundant.

Previously I have used sticks I have chopped up with my slasher – a sort of micro HugelKultur – works great but takes a long time to decompose and this was an experimental bed I expected to rework.

The next layer is manure – I used chicken manure because, like with most things I use what is readily available (and cheap). I mixed this rock dust (basically Bauxite – full of magnesium) and Dolomite to reduce the acidity of the manure and add calcium. I also use a rock dust mix which is significantly more expensive but has a range of trace minerals.

My soil is already full of micro-biota but is needed I would add some local inoculant.

Again I have been using this soil for some time and it already has a plenty of worms – both native garden and red wrigglers but again I would add worm eggs if needed.

The top layer is just the soil I have already dug out and is in good condition with a nice texture from years of feeding.

Then I just seed and give an initial surface watering in the normal way.

Watering

Now comes the critical bit – making the soil moist but not wet, which is what Gbiota beds are all about.

You simply do not get significant water movement until the soil is saturated (even in drip systems). So I put a hose into the inlet tube and keep on filling until I see water has partially filled the end sight tube.

I now have liquid water along the trench. This will start to flow sideways under hydraulic flow to the zone alongside the trench where it will start to wick upwards. It will also flow into the soaker zones at either end of the trench.

This is the difference between the sump and pump system where any excess water drains back to the sump for recycling while in the soaker beds we are aiming to fill the trench with enough water to flow and wick into the soaker zones but with no excess which would give us saturated soil.

As i already have a pump system I have connected the beds to the old manifold but this is just because it is there, a hand held hose works perfectly well.

I expected getting this right to be a bit of an issue but having filled the trench to a depth of 50mm the water had moved with no saturated soil remaining. Filling does not appear to pose any problems (unless you leave the hose running while you have a cup of tea).

Knowing when to re-irrigate is a bit more of an issue. I was hoping that I could just feel the soil at the bottom of the sight tube but having tried this I am not convinced as yet that just because the soil is still moisture in the sight that this means there is moisture throughout the remainder of the bed.

In this case I resort to my friend the auger and just take samples at various point in the bed until I feel the moisture level is getting low. This is the big danger with all Wicking beds – just keep on topping up with water when it is simply not needed – that’s when the soil starts to go putrid which means we are breeding the bad bugs.

For a quicker check I have planted some water sensitive plants like tomatoes and Chinese Cabbage which show serious signs of wilting when they lack water but spring back as soon as water is available.

Maintenance

The whole point of Gbiota beds is to breed the beneficial bugs that will eventually form part of our gut biota. In addition to the soil micro-biota we need to feed the macro-biota – specifically the worms.

There is a lack of critical research studying how the soil microbes move from the soil and become established on our gut. My hunch is that worms (and other macro creatures) play a critical role in this as they have a gut just like us so I am anxious to keep them well fed.

I have three basic strategies which all have the common requirement for avoiding those trillions of flies which love to visit when anything pongy is on offer.

In the first system I simple dig down to the base of the bed and reload – but I don’t like overworking the soil so I just dig a 200mm trench to one side of the ag pipe this time and the other side next time.

This won’t harm the bacteria and will only cause minor damage to the fungi with long hyphae but they the hyphae will soon regrow as the body itself has not been damaged.

The second approach is just to use those small compost bins which can be placed appropriately on the surface and just let the worms come by on their evening wriggle and take the compost down to the depths.

The third approach is to use the pathways as composting zones. I am simply laying down any suitable organic waste (eg food waste) and covering with my abundant supply of grass clippings.

This of course will block the paths as flow channels when we get these extreme weather events. The idea is that when one is forecast I will rake up all the semi rotted material onto the beds themselves as a mulch leaving a clear flow path to the flooding water. Only time will tell.