The Sustainable Garden

The Sustainable Garden - Wicking Worm Beds
9 October 2019

What better than a self sustaining vegetable garden to go with your sustainable home? We recently constructed a couple beside our orchard to improve the productivity of our vegetable garden, The design incorporates a wicking bed to minimise water usage and an integral worm farm to provide nutrients to the soil and water and to aerate the soil.

You can use whatever products you have available to construct the frame: excavate into the ground, sleepers, corrugated iron or a combination of both We considered all of the methods above during the design phase. We settled on using one of the Birdies 8 in 1 raised garden bed kits based on price, availability and simplicity. These beds provide a raised height of 740mm.

The key design aspect in that a wicking bed is that the soil depth should be between 300 and 350mm for optimum performance. Less than this and the soil may be too wet and greater a little to dry. Feel free to experiment if you would like.

Step 1 – Level the ground and erect the frames

Note: Protect the lining material.

The next step is to line the frame to hold water. Before commencing this step consider how, and if, you should conduct works to protect the liner of your choice. It would be a painful experience to complete the job only to find the liner has been punctured. We used the cardboard packaging over the internal threads and between the liner and the ground to provide protection.

Step 2 – Installation of the liner

A pond liner would be ideal to use; however, builders plastic (the membrane used under concrete) is effective if installed carefully. We doubled up the membrane to increase the protection.

Step 3 – Ag pipe installed and filled with 20mm road base.

Once the liner has been installed we now require a means to manage the water. A length of ag pipe from one end of the bed to the other is a great way to introduce water into the system. One it is in place; carefully backfill to the required water level with a material suitable for supporting the soil load while concurrently providing an area to hold the water. We used 20mm aggregate; however, any gap graded material (a material that will provide voids for the water) could be used. I have heard of tan bark being used; however, I think this could lead to problems down the track as it breaks down and compresses. Scoria would be a great option due to its light weight, high strength and integral voids.

You could get fancy here and install a water level indicator if you wish (ping pong ball attached to a stick with silicone and suspended in PVC pipe). I think it is overkill; but if it floats your boat get to it!

Liner, ag pipe and aggregate installed. Now is the time add the water just in case there is a leak – something that can be repaired easily now.

Step 4 – Install the drain. Now that you have tested the integrity of the liner it is time install the drain. A 20mm hole punched in the container at the high water mark. At the water level you want to achieve install a piece of PVC pipe; ensuring you cover the end with some weed mat or geotextile to prevent it becoming clogged. I used some old 20mm conduit we had laying about.

Step 5 – Lay a piece of geotextile or weed-mat over the water well in order to separate the soil and water (forgot to take a photo – sorry).

Step 6 – Make a worm house. You can buy a pre-made in ground system from Bunnings for around $32. Alternatively place a suitable barrier between the soil and your worms leaving a small gap to allow them to travel. I used some 300mm PVC pipe I had on hand and drilled some 20mm holes facing towards the soil.

The completed garden beds mulched and ready to plant out

So what was tools are required and what was the overall cost?

Tools Required:

Mattock, Shovel, Level, Screwdriver (screw gun preferable), wheelbarrow, drill with 25mm step drill bit and a stanley knife. As I made the in ground worm hose I also used an angle grinder.

The material requirements/cost to construct a single wicking worm bed are:

Birdies 8 in 1 raised garden bed $259

Builders Plastic (concrete membrane) free – off cut from another job. To purchaseit from Bunnings – $15

Ag pipe – again an offcut. From Bunnings -$31 – enough to do 2 beds

20mm single sized aggregate; 1m3 – $70

Geotextile/Weedmat – again off another job but from Bunning – $10

In ground worm farm free offcut of pipe- from Bunnings – $32

1000 composting worms – $27.50

Soil free (dug it out of the existing garden to capture the worms and microorganisms) – Garden mix; 1m3 – $53

Chook Manure and compost (free); from Bunnings – one bag each $10 total

Mulch 1 Bag- $16.5

Delivery of soil; free picked it up in my own truck- lets add $65 to be safe.

The cost to me using offcuts and leftovers was approx $350

Total if you purchased it all from Bunnings and had the soil delivered $5

Time to Complete?

The time to complete – I cheated and used an excavator where I could; but a bit over half a day with all of the materials on site. Degree of difficulty – pretty simple.

I have yet to realise the water savings or the improvement in garden productivity. It has been a very dry winter in and around Murrumbateman so saving water will be well worth the effort,

Given the cold climate in we won’t plant out the seedlings until after the Melbourne Cup (Note the frost in the photo). I have been caught out breaking this rule before. This will allow the compost the break down a little in the soil and for the worms to get active.

I will let you know how it fares over Spring and Summer.