Intro: Zero Water Biowicking Bed
Townsville is currently deep into water restrictions so now is the perfect time to be innovative, create urban food projects to reduce your lawn size (water guzzler) and you can do it using no drinking water at all - here's how I have been building zero water biowicking beds.
- Bed is 2.4m long, 0.7m wide and 0.6m high
- Total cost for the system is $270 and a few beers for your mates who help put it together (this is timer, rocks, growing media, inoculant, plants - the whole thing).
- If you have not learn about wicking beds or biowicking beds - a quick google and you will see why this approach is so effective for growing food in the city
Materials and costs:
- 2.4m x 0.2m timber sleepers - 8 in total and they are $15 each
- 200 micron black plastic - I used a 2m x 5m sheet and it was $27. Don't be cheap, get the 200 micron
- approx. 3m conduit around the 25mm diameter, a 90degree elbow and an end cap $12
- 0.5m3 of round river rock for the water reservoir $25
- some old bed sheets or towels - free
- 0.7m3 of 50% mill mud and 50% washed sand mix - make sure you use the mill mud. $30
- Plants and mulch $50 and make sure you read about what grows at the time of year you plant
- Timber screws for the sleepers $6
There are many ways to put one of these together so be creative, this is just the method I used recently as I have had a bunch of questions from friends after posting on social media.
Be creative, have fun designing and remember - choosing the right location for your bed and the right plants are critical.
Step 1: Find Free Water and Build Your Frame
Look for your air conditioner discharge points. You may need to slightly modify it to ensure it enters the bed approximately 150mm from the ground. I always measure the amount of water coming from the air conditioners when in use and size my beds accordingly. In Townsville, your food will need approximately 5L per day for every 1m2 of wicking bed - the water above came from the lounge room system and it provides >20L each day - more than enough.
Building the frame:
- Its best to have the hardware store cut the lengths to size
- I like to pre-drill holes with an 8mm bit and then screw the sides together with long timber screws
- After connecting a layer of sleepers, stack them as pictured (this is three layers high, each 200mm)
- If you don't want to build a frame, try using old IBC containers cut in half - they are perfect
Step 2: Line the Bed and Install Manual Fill Point
Lining the bed is critical so ensure there are no sharp edges below your builders plastic, its good practice to throw down some old cardboard or towels to help protect the liner. Carefully fold out the 200 micron builders plastic and cut to size making sure you do not puncture it. I like to use a staple gun to secure the liner at the tops of the bed.
- cut the conduit to be the diagonal length of your bed and add the end cap to one end
- add your 90 degree elbow and 600mm length of conduit to create your manual fill point if needed (visible in the video - right hand side of the bed and sticking out above soil)
- connect your dripping air conditioner to the rock reservoir zone using conduit and a 90 degree elbow (see video - I like to allow the connection to be disconnected if needed) at about 150mm from ground level - you will need a 25mm hole cutter and some muscle to get through the sleeper
- The system pictured also has a slotted downpipe running through it, this is a Townsville adaptation that allows low flows of water from the roof to flow into the water reservoir during cooler months when the air conditioners are sometimes off. It also supplies water to the bed during all rainfall events - its handy
Step 3: Build Your Water Reservoir and Cover It
Again, protecting the liner is key so its good practice to add some protective towels on top of the plastic as per the picture here. Then carefully place your round rock into the bed until your reach the desired height (this reservoir was approx. 200mm high).
Keeping your water reservoir working:
- you will need to carefully place sheets on top of your rounded rock water reservoir, this is to keep the growing media from falling into the water reservoir so make sure you don't rush it
- I like to form small wells like in the picture, this allows the sheet to soak up water from the bottom of the reservoir in times of need, it is also important to maintain oxygen in the system (important long term)
- you will need to add a water outlet about 1 inch below your max rock height, this is to allow the system to drain when full of water. I used the downpipe as the overflow however you could simply grab a 19mm seal as per my last instructable
Step 4: Add Your Growing Media and Innoculate With Beneficial Microbe Mix
You are now ready to start adding your 50% sand and 50% mill mud mix. I have tried lots of different combinations and find this the best for long term results (although straight mill mud works well, its just slumps over time and needs sand anyway).
- I make my own but you should be able to purchase some from your local gardening supplier and make sure you are specific about what you are using it for as you can purchase many different varieties. I love to use a product made here in Townsville - VRM, its magic
- The microbes stabilise soil temperature, product additional water, help your plants communicate and can prevent the system from going anaerobic. Lots of science, just google if you are interested - or flick me an email
I like to fill the beds right to the maximum with this mix as it settles a few inches over time. You don't HAVE to have the microbes but the biowicking system truly functions much better with them and its a great way to save on fertiliser costs whilst cutting down on your household waste.
Step 5: Choose Your Plants Wisely and Mulch
You are now ready to plant - some important considerations when selecting what to plant:
- how much sun is the bed getting - more than 6 or so hours = full sun
- I planted wind tolerant food at the end of the bed most exposed and big leaved stuff like silverbeats and bok choy down the more sheltered end - this also saves water
- plant stuff you will eat, simple but not always followed
- consult a good website like www.gardenate.com and talk to local experts - I will soon have an urban food calendar for Townsville to share due to some nice work from our local council
- record what you plant and improve each year
- if getting seeds I would strongly recommend www.greenharvest.com.au and wicking beds will rear seeds however best results are found when transplanting directly into them
Remember to mulch, it saves water, cools the soil, protects the soil biology, prevents weeds and just looks much better.
Thanks and happy growing (and eating!)