Sunday, 10 March 2013

Raised wicking garden bed howto guide

So I finally got the time to make the raised wicking garden bed.
So far I have found it uses MUCH less water than anything else we have.
It has been in use for around 1 week, and has used around 20% of the reservoir (around 100 litres in one week, most of it in the first day).

Here are some directions to follow:
(Let me know if the directions are confusing or if you need clarification on anything)

Firstly, make sure your garden bed is 60cm high. If it is less than 60cm, just dig down deep enough to make up the difference, as I have done. Make sure the bottom is level (use a spirit level.)

Once you have dug down, make sure there are no pointy bits either in the soil at the bottom or anywhere on the sides, as these will puncture the plastic liner and render the wicking part pretty much useless.
I did this by adding mud to the sides and then smoothing it with my hands.

Next, add the plastic liner. Make sure you stay outside the garden bed and never stand on the plastic liner as your pressure may puncture the liner. I used two layers of 200um builders plastic.
Add the PVC pipe, the elbow join and the slotted AGI or drainage pipe. This will allow you to water the garden bed from the bottom.

Next, add 30cm of 20mm scoria and add 30cm of water. Use a rake to gently level the scoria.
Cover with a geo filter. (You can use a weedmat, but I have heard it is not so good for water transmission.)

(As you can see, I did not add the water at this point, relying instead on a spirit level.)
Next, add the drainage pipe (I just used a clear bendable pipe which I cut back later). This drainage pipe is there to ensure the soil does not get waterlogged. I used more geo-filter on the inside to protect the drainage pipe from being clogged and from nasties from crawling up the pipe all the way. Put this at the level of the top of the scoria. You will need to cut into the builders plastic at this point, but make sure you do this at the 30cm mark where the scoria level is! Take a look at John's blog as he uses a better drainage overflow system which I would encourage you to do if possible.

Next, add 30cm of dirt on top, again making sure you do not lean nor stand in the garden bed. Add free draining rather than clay soil to encourage good wicking action.

(As you can see from the photo, it was night-time by the time I was up to this stage. There was plenty of  carting scoria and dirt back and forth!)
Once you have done this, add your seedlings, put a layer of straw to suppress weeds, add nitrogen back into the soil and further reduce water evaporation, and off you go! Make sure you cover the PVC pipe with something or you will end up with mosquitoes and other nasties getting into the reservoir, and you do not want that!

Once you have watered the plants in, you can stop watering from the top and let the plants get their water from the wicking action.

You can check the water levels in a few ways. The easiest way I have found is to simply use a piece of wood as a dipstick, dip it into the PVC pipe and see what the water level is. The image below is after 1 week of use, the black line is just above the full mark, and as you can see it has used very little water.

See below for a side view of the garden bed.

<- PVC pipe
<- Plants and straw goes here
<- Top layer of dirt goes here

<- Geo filter+drainage pipe at the 30cm mark
<- Scoria goes here
<- Outlet for drainage pipe and the brick layer
<- (Below soil) Bottom of the garden bed.

 Here is a breakdown of the approximate price:

$50    3/4 cubic meter of scoria
$50    1 cubit meter of quality dirt
$30    200um builders plastic
$30    30m 50mm AGI slotted pipe
$5    1m 50mm PVC pipe
$7    50mm x 50mm x 50mm tee joint (to connect the PVC pipe to the slotted AGI pipe)
$200  Birdies 40mm raised garden bed (approx 3m long x 80cm wide)
$30    30m x ~1m geo filter (goes between the scoria and the dirt to ensure the dirt does not get into the reservoir)
The bricks and wood were free as they were lying around the house. :)

Total price: Around $400-$500 depending on what you use and what you have lying around the house.
Total time taken: About 12-30 hours depending on what you need to construct and how much experience you have in the garden.
Total fun: EXTREME!!!

Current plants in the wicking garden bed: Eggplants, Beans, Spinach, Silverbeet, Snow peas (still germinating), Radish, Carrot (yet to start germinating), Onion (still germinating) and Capsicum (developed plant).

(Left to right: Silverbeet, Radishes and Spinach)

Next step: Adding worm towers to the garden bed!

So get out there, get dirt under your fingernails and most importantly, enjoy yourself!