This wicking worm garden builds off the raised no dig garden bed method
Advantages: Similar to the no dig garden, the wicking worm garden is easier on the back as it is at a higher level and no digging is required. Also less watering is required than conventional garden bed.
Disadvantages: More expensive and complicated than conventional garden bed.
Location / Space
Choose a location for your wicking worm garden that has the best access to sunlight, then mark out a space where you would like the bed to go. As with the no dig garden the advantage is that it can be placed over any surface such as paving or concrete.
Making a Wicking Worm Garden Bed
The wicking worm garden is the essentially the same outer structure as your raised no dig garden bed and the same materials can be used to form the outer edging. The main difference is that this garden needs to be able to hold a reservoir of water that will “wick” up through the soil to the plants. This means that the lower inner surface of the structure needs to be sealed. It is very important that the ground is level as this provides an even wicking action throughout the garden bed area.
As with the raised no dig garden bed, you need to make sure that the wicking worm garden bed outer structure is solid enough to hold the soil weight and reinforce the edges as required, similar to how a retaining wall works. Containers that already hold water such as old bath tubs and old water tanks are ideal for a wicking bed as no additional work is required to seal the inner surface to hold the water.
If you are building the wicking worm garden bed on a soil surface, there are 2 options for how you can set up the structure height.
Option #1 – If the amount of material you have for the outer structure is limited, you can dig a hole in the inner area of the marked out space around 20cm deep in the ground to hold the water and line this hole with pond liner or similar plastic. I have found that a pond liner works best, as builders plastic tends to be a little too thin and it is too easily pierced (in my first garden bed I used builders black plastic and despite my best efforts to remove all rocks it now leaks).
The overflow point of the water reservoir then becomes the ground level. The outer structure can be placed around edge of the hole on the level ground to form the raised garden bed above the ground. Make sure the raised section of the wicking worm garden bed is at least 30-40cm high to allow enough room for the vegetable root growth and the sand/rock and soil required for wicking.
Option #2 – If you prefer a higher garden bed then you can use the soil surface as the base of your water reservoir. This means that the height of the surrounding structure needs to be at least 50-60cm high to allow enough room for the water reservoir and the soil and sand/rock.
Note the plastic lining does not need to be the full height of the garden bed, only high enough to hold the water 20cm deep.
Once the base of the wicking worm garden bed is lined with plastic to hold the water, the next step is to use some pipe that will fill the garden bed from underneath the soil. This can be done a number of ways, but to ensure that the water is filled evenly throughout the bed, I like to extend the pipe for the entire length of the bed as shown below.
The stormwater pipe with holes drilled underneath is ideal for directing the water throughout the length of the garden bed providing an even fill.
Next step is to either fill with a course material to aid in water drainage, or add underground water tanks. I have used both these methods in my wicking beds.
1. Filling with Gravel and Sand
Fill the base of the wicking worm garden bed up to the height of the top of the stormwater pipe (approximately 10cm) and level out.
Place geotexile over the gravel surface (this is to prevent the sand from mixing in with the gravel). Add a layer of sand on top of the geotextile for the remaining 10cm – the sand acts as a sponge to help wick the water into the growing soil
Level out the sand layer and add another layer of geotextile over the surface of the sand. This is the level that the water will soak to. Its now time to add the overflow pipe to prevent the garden bed soil from flooding. Drill a hole through the side wall and liner of the raised bed in line with the height of the sand surface and then push another smaller pipe through and cover with a small sheet of geotextile to prevent sand and soil from leaking out the pipe.
Then fill the rest of your wicking worm garden bed with your 30-40cm deep soil mix that is light and free draining – I like to mix a little sand through this soil to aid with the wicking process. Cover the soil surface with some mulch, then you are ready to plant out.
The final step is to add the worms. You can use an old flower pot for this. Simply drill a few holes up to 1 inch diameter in the base and sides of the pot. Dig a hole in one of the corners of the wicking worm garden and place the pot in the hole. Fill the pot with worms and vegetable scraps and cover with some old carpet. The worms will eat through the scraps and pass in and out of the pot into the garden bed. The more scraps you feed them, the more they will multiply providing valuable nutrients to your garden. The advantage of the wicking worm garden bed is that the space the worms have available is much larger than your conventional worm farms. This means that the more you feed them, the more they will breed and consume your kitchen scraps. Note that worms will stop breeding when they have filled the space you keep them in, so this is why worms farms need constant expansion and also why the wicking worm garden bed is an advantage.
2. Filling with Sand and using underground tanks
This method is very similar to the 1st wicking worm garden concept, except that in this case you use underground tanks to store the water replacing the need to fill the lower 10cm with a free draining material such as gravel.
I used plastic crates for my tanks and cut a hole in the sides to slide the stormwater pipe, and overflow pipe through, then wrapped them in geotexile to prevent the sand from entering the tanks and pipe. Because the plastic crates were a little higher than the 20cm depth I needed to recess them in the ground, so that I could cover the top with sand.
Next step is to fill with sand 20cm deep covering the top of the tanks, add a layer of geotexile and then fill up the bed with your soil mix
Then add the worms as per the 1st method and your done!
Note that there are many different ways to make a wicking wiorm garden bed with some people using different materials and methods to what I have described. The purpose of this section is to describe the concept so you can use your own imagination and innovation to come up with your own style of wicking bed.
Here are some photos of the wicking worm garden beds that I have created…
This one is built up using the 2nd method (underground tanks).
Here is my latest wicking worm garden bed, using thin timber as the frame (bolted to 2 X 4 timber posts)
Below is my largest wicking worm garden bed (3 X 1.5m). This was the first that I made using builders black plastic as the liner – It is now leaking, so I will need to reseal at a later date with some pond liner.
Unfortunately my large wicking bed had a small leak because I used builders black plastic instead of the pool liner. I have decided to demolish this garden bed and create 2 smaller beds to create better access for the kids. I will use pool liner in the new beds to prevent leaks.
Here is a picture showing the layers of the wicking bed. This one has rock at the base, followed by some weed mat, then a layer of sand and finally the growing soil.
Wicking Bed – Mark #2
The following pictures show my latest wicking bed creation, built out of recycled timber and corrugated iron sheets.
The frame – I used larger posts and rails to support the corrugated iron sheets.
Next step was to seal the lower portion of the garden bed and build in an underground tank and overflow pipe. I used pond liner to hold the water as this is much stronger (and thicker) than the builders plastic. For the underground tank, I used a plastic crate turned upside down and inserted the overflow pipe at the top of the crate.
Here you can see the overflow pipe, which is inserted into the top of the crate and pushed through the plastic and iron sheet. It is important to make sure that you seal the pipe where it pushes through the plastic to avoid getting water leaks between the plastic and the inner side of the iron sheet.
Next step was to create the underground void (tank) and I used geotextile material draped over the tank. The fill point is straight into this tank via some poly pipe. I secured the pipe with a few concrete tiles. The geotextile has plenty of overlap to make sure that the sand and rocks does not go into the void section.
Then fill with sand, or whatever else you choose to use for your wicking material. I make sure that the sand fills to above the top of the crate to help with the wicking process up into the soil.
A layer of geotextile to separate the sand and the growing soil.
Filled with compost fresh from my hot compost bin! A great way to use kitchen scraps and lawn/garden cuttings. Keep the depth at least 30cm for growing vegetables.
Time to plant out. I used some pea straw to keep the surface free from weeds.
Here is another wicking garden bed I put together using a plastic food storage bin.
This link gives some details as to how it was put together and the materials used.
Preparing the soil
I have used both the layer method described in the no dig garden section and also just filled with a good light garden mix from the local garden supplier. The main thing is to make sure the soil is not heavy so that the water can freely wick up into the roots of the plants without too much effort. A good mix of compost, organic matter and light free draining soil should be fine. Over time the worms will help to improve the soil structure assisting the wicking process.
Follow the same process as mentioned in the “growing in the ground” section and add lime when required to keep the soil slightly acidic for vegetables. One of my wicking worm garden beds contains strawberry plants this year, so I have made the soil more acidic by adding sulphur and some peat moss.
In the summer, make sure you check the water height every week or so and top up as required through the fill pipe – you will know when it is full as the water will start to drain out of the overflow pipe. Keep adding organic matter to your wicking worm garden each season just as with your normal garden beds and make sure you keep the food up to the worms so they keep multiplying.