Wednesday, August 24, 2011

:: Raised Wicking Worm Garden Bed Instructions ::

These detailed instructions were compiled by my husband while he designed and built the first of the Raised Wicking Worm Garden Beds. We installed a total of four of these during our PermaBlitz in October 2010 (all posts on the Blitz & Follow Up's can be found here). We did 6 weeks of hard work & prep leading up to the Blitz, including building this 'trial run' raised wicking worm garden bed (and assembling the other 3 modular garden beds together too), often working at night and all weekend. There are two reasons that we did a 'trial run' on the raised wicking worm garden beds. One was because it was a complicated and heavy project for our PermaBlitz ACT 'volunteers' to have to work on during a one-day backyard blitz, without also having to work out the design and complexities on the day. Plus, it cost us a reasonable amount of money too, so we wanted to 'get it right'. While it was hard work building this raised wicking worm garden bed system, but we think it was worth it, and have had great success with growing a huge variety of produce in our 4 beds. We don't have exact figures for total costing, or produce grown & harvested, or anything like that... I guess we were just too busy getting on with the creating & the growing!
You can view photos on Picasa, as this might help explain some of the instructions below: 


There are numerous ways to create a wicking worm bed, many of which are simpler and cheaper than the approach documented here. The design implemented in this document has been compiled to make best use of the resources available on the site at the time of commencing the project.
Why Raised Wicking Worm Garden Beds?
  • Wicking beds are extremely water efficient.
  • Water is held below the growing medium, so the deep (water seeking) roots of your plants find what they are looking for.
  • Finer shallow nutrient seeking roots avoid damage from water while collecting the nutrients from the worm castings.
  • They retain rainwater, but are also easy to 'top up' with water as needed from your rainwater tank or even town water
  • Being raised, they are easy to garden in, and are great if you have poor soil, or only concrete or paved backyard
How does 'Wicking' Work?
Wicking garden beds work through a process known as Capillary Action.  This is essentially a phenomenon where liquids defy gravity and are drawn up into fine tubes or porous materials. The movement is a result of the surface tension of the liquid (caused by cohesion within the liquid) interacting with the adhesion between the liquid and the medium. There is a mathematical equation that can be used to determine the distance a liquid will travel in an upward direction based on the diameter of the tube (or capillary) the liquid is moving through.  Trying to directly apply the mathematical equation of Capillary Action to our Wicking bed project is not practical however the concept to take from the equation is:
The smaller the spaces between particles the higher water will rise through Capillary action.  This means that water will rise higher through sand than it will through stones due to the sand having finer practicals, which will result in less space between particles creating finer capillaries.
A common everyday example of this phenomenon is a Paper towels using capillary action to draw liquids up from wherever they were spilled.

Wicking Bed Layer Depths

The diagram above represents the layers inside the planter box.  The difference between the planter box height of 820mm and the 700mm (100mm much + 300mm Growing Medium + 300mm Gravel) of layers represented is levelled filled soil foundation beneath the base of the reservoir.  NB. The maximum wicking action possible with the type of growing medium we used is about 30cm!

Quick Reference Steps
  1. Dig footing trench and install garden bed so it is level
  2. Fill the garden bed to the Base line with earth from the footing trench and level
  3. Line the garden bed with the pond liner (User tape as needed)
  4. Cut, Screw and Silicone the high water drain pipe into place
  5. Lay the watering pipe + geo textile strip in place (tape if required)
  6. Fill the lined garden bed with gravel until level with the drain pipe and level it out (15-20 Barrow loads)
  7. Fill the reservoir with water using the watering pipe and top-up gravel if required
  8. Lay the Geo textile over the gravel (and drain pipe)
  9. Place the worm feeding tube in a convenient location
  10. Fill the garden bed up to the Soil line with organic compost and level it out (15-20 Barrow loads)
  11. Spread the worms over the level compost
  12. Cover the soil and worms with (sugarcane) mulch

Resources/ Materials Used

  • Corrugated Iron Planter Boxes  (Birdies Garden Beds - Note: we choose Birdies because they had an online special where you get the 4th one at 70% off, they could be set up in the dimensions that suited us, and were Aussie Made & Owned. However, we (mostly R) spent a lot of time putting them together! You can purchase, or source, other brands like Tankworks, which get delivered already assembled, but these cost more. You can also look to use wood or other materials.
  • Pond Liner (4m wide, cut to 3m length) (Bunnings $34.95/m x 3m = $104.85)
  • Geo Textile  (Bunnings)
  • Slotted Ag Pipe – We used old un-slotted ag pipe  that we had, which was not as convenient (we had to drill holes in it), however, it still did the job
  • 7mm Graded Round River Gravel (Local landscape supplies company - $50m3 x 8m3, plus $47 delivery fee, NB. this was more than ended up needing)
  • Organic Compost (Local landscape supplies company - $48m3 bulk delivered rate x 5m3, again more than we needed for this project, but we have used it on other garden beds)
  • Organic Sugarcane mulch (Bunnings $16.48 per bale)
  • Selly’s Silicone  (Bunnings)
  • Drainage assembly x2
           -    25mm ...... (Bunnings)
           -    25mm screw in plug  (Bunnings)
           -    25mm Join (used for internal filter attachment) (Bunnings)
  • Worm Feeding Tubes (x 4)
            -          90mm PVC pipe  (Bunnings)
            -          90mm PVC plug (Bunnings)
            -          90mm PVC thread  (Bunnings)
            -          90mm PVC screw on cap  (Bunnings)
  • Worms (Bunnings $94.00 for 2000) (approx 1000 per bed – the more the better if you can afford it)
  • 25mm Irrigation pipes - cut & opened to use for covering 'wing nuts' inside the Birdies raised garden beds (We use some we had salvaged from damaged irrigation system)

Tools & Equipment

  • Power drill
  • 35mm hole cutting drill bit (steel grade)
  • 10mm drill bit (only required if not using slotted ag pipe)
  • Wheelbarrow
  • Shovel
  • Rake
  • Soil Spreader (optional)
  • Scissors (for cutting geo textile and pond liner)


Watering Pipe

Slotted ag pipe would have been ideal for this purpose, however as we had some regular ag pipe on hand we used it instead.
1.   Made from ag pipe reclaimed from deprecated Grey water System
2.   Cut pipe to length so that pipe runs from the top of the planter box, down to the base of the reservoir, along the length of the planter box  (and optionally back up the other side).
3.   With a large bit drill holes approx. 5cm apart along the length of the pipe that will lay flat at the base of the reservoir
a.    Holes don’t have to be exact, just make lots of them all along the pipe on all sides
4.   Attach a piece of flyscreen, shade cloth or other filtering medium over the open end of the pipe (if you are not running the pipe up both ends) and fasten in place using some cableties
a.    Don’t cut the ends of the cable ties as the will leave sharp edges that may puncture the liner.

Worm Feeding Pipe (90mm diameter PVC)

1.   Cut 90mm Diameter PVC Pipe to 400mm length
2.   Glue cap to base end
3.   Drill holes for worm access along the length of the pipe

Installation Steps


  1. Dig footing trench
  2. Partially fill footing trench with gravel so planter box can be installed on level ground
  3. Fill base of planter box with clean fill up the 150mm mark and compact/level as needed

Creating the Reservoir

4.   Use the 35mm hole cutter bit to drill holes at the low and high water points for the drainage pipes.
a.    Place the drainage pipe assemblies loosely into the holes to prevent the sharp edges cutting the pond liner in the following step
5.   Line the inside of the planter box with- builders plastic so that it hugs the edges and is flat on the base, with the remainder hanging over the edges of the box.
a.    IMPORTANT: No seams, this will hold water.
b.    It doesn’t matter if the liner does not make it all the way to the top edge of the planter box, as long as the edges are higher than the high water line.
c.    If the liner has been laying in the sun for a while it will be a lot easier to work with than if it is cold and stiff.
6.   Cut a small hole into the liner and Install the high water drain outlet
a.    Make the hole smaller than the drainage pipe and use the thread of the pipe to screw it in keeping the liner in very tight contact with the pipe.
7.   Apply excessive amounts of silicone around the drainage join on both sides of the liner and around the metal edge and then carefully screw the assembly together.  Tighten as needed being careful not to rotate the pipe and stress the liner.
8.   Lay the assembled watering pipe in place and duct tape the vertical end in place at the middle of one end
9.   Place the water pipe geo textile strip over the pipe and carefully cover with gravel so the gravel holds the geo textile over the pipe.
10.                Continue to fill with gravel (approx 15-20 barrow loads) and level as needed at the high water mark – This is the most back breaking part of this project.
11.                Fill the reservoir with water via the watering pipe. This will result in some settling of the gravel and may require a top-up to bring it back to the high water level.

Growing Medium

12.               Once the gravel is level is even at the high water level, roll out the geo textile with overlap as appropriate to cover the gravel filled reservoir.
13.                Leave small amount of the geo textile edges running up along the planter box walls to contain the growing medium
14.                Shovel 1-2 barrow loads of the organic compost into the bed on top of the geo textile layer.
15.                Place the worm feeding tube in the desired location building up the compost around the tube for stability
16.              Start shovelling loads of the Organic Compost (approx 15-20 barrow loads) into the garden bed until the compost is level at around 5cm below the top of the garden bed.
a.    The soil will settle and the subsiding depth can be filled mulch
17.                Cut the excess pond liner away using sharp heavy duty scissors or a box knife and save the leftovers for future projects (fold the edges back under the outside edge of the pond liner and inside the planter bed if required) .

Worms & Mulch

18.                Distribute the worms in a mix of coir/bedding/food over the surface of the soil.  (They will be covered with mulch)
19.                Cover the growing medium with organic sugar cane mulch
20.                Place some worm food grade food scraps into the worm feeding tube.

Thoughts on Improvements

  1. Screw the external  edge of the drainage pipe fittings into the corrugated iron to prevent it from rotating when removing the plug to mitigate the risk of breaking the seal
  2. Use 25cm or more width of geo textile to wrap the watering pipe to avoid the need for cable ties
  3. Using pre made planter boxes without the need for wing nuts on the inside would eliminate the need to cover the wing nuts to mitigate the risk of tearing the liner.
  4. Use Sand instead of Gravel for reservoir
  5. Source a sandy soil instead of organic compost for the growing medium
  6. Instead of installing with the reservoir and growing medium above ground, dig the reservoir into the ground to make filing with sand or gravel much easier
  7. Don’t bother with the low water drainage pipe.  Just introduces delays waiting for the silicone seal to dry and is a critical point of failure if it leaks.
  8. Think about the required size of the overflow pipe in the event a downpipe is feeding the reservoir with roof diverted stormwater.
  9. Buy a Soil leveller
  10. If working with above ground reservoirs, build a ramp so that barrow loads of gravel or sand can be dumped directly rather than being shovelled at both ends.
  11. Use 90mm diameter PVC tube for the watering pipe to allow accelerated filling when connected to house stormwater downpipes
Resources We Used
Please let me know if you find any discrepancies in our information, remember that R worked some late hours on this project and he did these instructions up in case anyone in the PermaBlitz ACT team who wanted them. If anyone is interested, I am sure I can make a downloadable PDF, just let me know!