Corten Steel Wicking Beds

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So what is a wicking bed ?

It's essentially a self watering garden system. You can see in the photo's its a fairly basic but highly effective system.

It's very water efficient and low maintenance with the added benefit of having your garden watered when you go away on holidays or as in my case when school holidays come around and the place is deserted for weeks.

I decided to re work a section of our garden that had very little soil depth and near zero drainage. During times of heavy rain the ground would flood and not much was really growing. With the wicking bed having an overflow port fitted even if there are heavy rains the excess water is drained away from the garden beds.

Supplies:

I had to create four garden beds and it was to suit a existing and specific space so the size dimensions and quantities will need to be adjusted to suit your own needs.

The list below is what I used to make one garden bed.

I sourced all my materials except the Corten steel from Bunnings.

1 x 2400mm x 1200mm sheet of 2mm Corten steel cut into 3 x 400mm x 2400mm strips.

1 x 6m length of 10mm straight reo bar.

1 x Galvanised metal flange nut with a 20mm internal thread.

1 x 20mm threaded plastic irrigation connector with a 15mm barb.

1 x 2m x 4m sheet of pond lining.

1 x 10m roll of geotextile.

1 x 400mm of 50mm pvc pipe.

1 x 50mm pvc elbow.

1 x 50mm pvc cap.

1 x Roll of packing tape.

1 x 7m length of 65mm split ag pipe.

3/4 m3 of 20mm drainage scoria.

1m3 or garden soil.

A few buckets of sand.

Pinchweld rubber (optional)

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Step 1: Creating the Frame

I began by cutting the reo bar to suit the existing size and shape of the garden bed. I bent the reo bar to suit the rounded side of the bed and tacked the reo bar frame together. I then proceeded to cut the Corten steel strips to suit the reo frame. Because I was digging the garden beds out to depth of 100mm the width of my Corten steel was cut to 400mm to allow sufficient soil depth and to create a big enough water reservoir. I placed the reo bar at 100mm high from the bottom edge of the Corten steel. With the 100mm depth of the excavated depth of the garden bed added I had used the reo as a guide for my scoria depth later on. On one of the flat sides of the Corten steel just under the reo bar I drilled a 15mm hole and welded the 20mm threaded steel nut on the inside of the frame to use as my overflow hole.

Step 2: Excavation and Levelling

Next step was to excavate the existing garden bed to a depth of 100mm and remove any rocks or sharp objects. I also added a thin layer of sand to level the ground. This doesn't have to be perfect as the water reservoir is quite large. The key is to remove anything that might puncture the pond lining.

Step 3: Fitting the Pond Lining

I draped the pond liner into the garden bed and roughly taped it into place, making sure it is above the height of the reo bar by about 50mm everywhere. Don't stress to much as the tape will be removed later on.You should now add some water to assist the pond lining into finding it's on place and to level itself out. Just enough to cover the bottom and around all edges. As the water is filling up gently remove the tape as the lining starts to tighten and find its own place. Once it has you can put a small hole in the pond lining inline with the welded in place steel nut and attach the barbed fitting to act as an overflow. Have the barb facing into the garden bed so it isn't knocked off from people walking past.

Step 4: Fitting AG and PVC Pipe.

The next step is to connect the pvc pipe together and place the 90 degree elbow into the slotted AG pipe.Take the straight section and add the elbow to one end. Tape this end into the AG pipe and create a roll of Ag pipe in the bottom of the garden bed. Add some scoria to keep it in place and have the pvc pipe rest against the corner. Place the cap on top to stop any foreign materials being placed in and to stop mosquitoes breeding in the water. The AG pipe is important as it create's an extra water reservoir as the scoria cannot displace the water.

Step 5: Scoria, Geotextile and Soil

Add the scoria to the level of the drainage barb being careful to to break it.

Add two layers of Geotextile fabric over the top of the scoria making sure it reaches all the edges. This stage is important as the fabric stops the soil from mixing with the scoria and also creates the wicking effect.

Now add a good quality soil/compost mix until its just below the top height. Allowing some space for mulch to be added later.

Also fill the reservoir up via the pvc pipe til it runs out the overflow pipe to make sure its working correctly.

Step 6: Finishing Off

Now you can plant your plants!

We chose to create a bush tucker garden so we planted all indigenous plant from our local area and a few from other areas to see how they would go.

We also added pinch weld rubber to the top edge of the Corten steel to stop any little hands cutting themselves. It's reasonably expensive and wouldn't be need needed in the home environment.

Water the plants in from the top for the first few weeks so the roots can grow downward and allow the wicking process to begin. Then you can add mulch to stop the surface from drying out.

The wicking bed style of garden bed can be styled to suit any size or shape its just up to your imagination ! It doesn't have to be as large of complex as ours are, they can be made from old plastic tubs or any material that will hold water.

Have a go and see what you can create !!

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    15 Discussions

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    tytower

    4 weeks ago

    I'm intrigued by how long you think that corten steel will last ? Its high tensile isn't it and 2mm thick with soil up against the inside . My guess would be 5 years before its rusted through and unsightly but you may think or know differently?

    4 replies
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    Stephen24autytower

    Reply 27 days ago

    It’s my understanding that Corten steel is designed to rust and that rust then becomes the protective coating. Many places around our area are using it for garden beds and garden boarders so I would assume it would last longer than 5 years but have no information to prove this !

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    hreidStephen24au

    Reply 27 days ago

    It’s my experience that oxidized layers are good barriers against continued atmospheric corrosion, but when buried, that patina is a catalyst for runaway degradation.

    Hope I’m wrong, but you may want to line the inside all the way to the top, mate, just in case.

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    JohnC430hreid

    Reply 23 days ago

    too late. it has already been built. yeah I also think the steel will rust fast. 2 mm will be penetrated within 1 year and then the water will start leaking out from the sides making the area around look interestingly like it is winter, even in the summer.

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    Stephen24auJohnC430

    Reply 22 days ago

    Because of the pond lining and the overflow outlet the water never comes in contact with the steel frame. Also see comment above about steel garden edging.

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    Stephen24au

    22 days ago

    3. How does it last, if it’s rusting away? What would be it’s Lifespan?Rusting away is exactly what isn’t happening with Weathering Steel. Because of its chemical composition, corten steel exhibits increased resistance to atmospheric corrosion compared to other steel. The steel actually rusts on the surface to form a protective layer we refer to as a ‘patina’(because we’re posh!)
    The corrosion-retarding effect of the patina is produced by the particular distribution and concentration of alloying elements in it. The patina develops and regenerates continuously when subjected to the influence of the weather to maintain a protective coat.
    Another way to put this is by way of comparison. Normal steel develops rust that is porous with tiny pores in the surface that the eye can’t see. This rust does not seal the steel surface, the rust process therefore never stops and so, tends to flake. Whereas with Weathering steel, the patina produced is much less porous.
    The rust ‘patina’ develops under conditions of alternate wetting and drying. To ensure a stable patina develops, this natural cycle is key and the process should never be rushed with salts or acids. The rusting occurs on surfaces where oxygen is freely available. This means that in the ground, rusting happens very slowly due to low oxygen availability.
    In terms of the lifespan of Weathering Steel garden edging, local conditions such as humidity, salt (soil salinity), acid (soil acidity), soil density (oxygen availability) and sulphur content will affect this. Proximity to salt water is another factor that speeds oxidation up. Under ideal circumstances the weathering steel used in garden edging will last for many decades (maybe even 100yrs!) and in bad conditions expect at least 10 years.

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    billbillt

    27 days ago

    Great idea!.. If I live long enough to build something like this, I will have to use concrete/brick structures instead of steel....

    1 reply
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    JohnC430billbillt

    Reply 23 days ago

    "if I live long enough..." so start now....

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    Galt

    25 days ago on Introduction

    Interesting concept that I've seen friends use in Oz, with the stand-pipe reservoir & drain tile. I believe the steel used is similar (or the same) as the stuff they use for shipping containers. We are planning on cutting up a few and I was thinking of painting the cut out pieces with an epoxy or polyurea to add to its rust resist.

    The real trouble, as with wood that lies in contact with the soil, is right at ground level where it's likely to stay moist and accessible to the air. My only concern with the bottom staying real wet would be propagation of anaerobic organisms since plant roots like good oxygen exchange and mainly aerobic organisms. I've also seen a similar execution of the irrigation system incorporated into Hugelkultur beds in permaculture.

    Another approach, if and where an affordable and appropriate steel may not be available or viable, would be maybe reinforced lightweight concrete, I've seen some pretty cool -ables on making l/w concrete raised bed panels that were pretty thin (like maybe 3-1/2") and had cast in interlocking corner overlaps that allow them to be pinned together using pieces of 1/2" or 10 mm coated rebar. With some buttressing to stabilize them, raised beds are real nice for old farts like me if you lay a piece of weather proofed 2"x6" or 8" across the tops as a seat to work from. Very nice for vegetable gardening, especially if ya don't get up and down so good.

    And finally, we do something similar, but route what's called "leaky hose" irrigation in the substrate. It's the rough porous rubber hose that's made out of recycled tires. We hook it up to a manifold and run the hose through the end of the bed to daylight and on a slight slope, then cap the end with a screw on fitting so that it can all be drained down and left in place to over-winter. The hose is on a timer with a filter & pressure reducer, all controlled by a cheap garden hose timer. Also use buried PEX to feed the beds so that the sun doesn't super heat the hose water. At season's end the junctions, which are set in vaults that allow access without digging, get compressed air blown through them once disconnected at the both ends, kinda similar to the way a lot of underground lawn irrigation systems work.

    Nicely done and well presented.

    1 reply
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    Stephen24auGalt

    Reply 25 days ago

    We’ve used the wicking style extensively in our school garden and they’ve always worked very well. Never tried it with the steel but I’m confident it will work

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    shalnachywyt

    27 days ago

    While along with others, I hesitate to use any type of steel (where the heck would you get something like that in the US without having to take out a loan in order to buy it? Then there's the fact that in my climate (NE Tennessee) that would probably rust so darn fast...) I like the idea of burying some, what looks like to me, drainage pipe on the bottom. I would probably use smaller 1/2" PVC pipe with holes drilled in it because of the smaller size of the beds I have. At any rate, nice idea! It certainly is a great water saving device. Now I need to go outside and water all my plants because its' been 30 degrees C and up the last few weeks with no rain. :)

    1 reply
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    Stephen24aushalnachywyt

    Reply 26 days ago

    It will be an interesting experiment to see how the steel lasts. Our local council has used it extensively around the area so there might be a lot of replacing going on in a few years!

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    seamster

    4 weeks ago

    Very nicely presented, and full of great tips. Your finished beds look excellent! : )

    1 reply