Wicking beds

UPDATE: wicking beds lined with builders plastic do not last -- they develop leaks. Please read here for more info.






It's been a while between blog posts, particularly those concerning house projects. I have a lot to catch up on, and I've now finished one of my employment contracts and so should hopefully have a bit more time to blog. There are a few things I want to write about:

1. wicking beds successes and failures (below)
2. acrylic secondary glazing and some of the learnings there. Not all is resolved, but is getting there
3. failed project: Washing machine drain to front yard (pipe blocks)

I won't write about all these here, I will just focus on the wicking beds, but I hope to get to the others in coming weeks.

Gardening Australia (the only TV program I've watched for the past 6 years -- about an episode per year) has a great website about wicking beds. Basically, they cause the garden bed to be watered from below, by the process of the water wicking upwards through the soil. This means that the driest soil is right at the surface which minimises evaporative losses. In our ongoing attempts to reduce our water use, we wanted to build some so that we didn't need to water so much.

So far, I've built two using different materials, but both employ the same principles.

We built a round one first, using some salvaged corrogated iron, with help from permacultureSA.  I cut it so that the corrogations are vertical, and then pop riveted it into a circle (diameter ~ 2 m). The top was sharp, so I put a piece of hose all the way around held on with cable ties through holes I drilled into the corro. Underneath, I removed all the soil/mulch down to the clay, and made the bottom smooth. I made the inside walls of the bed as smooth as I could. Into this went builders' plastic (orange). This holds the water. I put two layers, but if I did it again I'd put 4 layers -- it is essential that it doesn't leak. There is an overflow pipe about 1/2 way up the walls, which are 400 mm high.
Into the builders' plastic, I put upside-down polystyrene broccoli boxes (these can easily be got for free, since they are not allowed to be reused), cut to a height of about 200 mm. I drilled holes in their bottoms and cut wedges from the tops to allow water to easily move through them. I also put a length of PVC pipe across the bottom, bending up and poking out the top. On top of this I lay geotextile, allowing it to form pockets all the way to the bottom of the reservoir in places. Then I filled the top with soil, being careful not to let soil get below the geotextile. First time around, all of the filling steps were done by the permacultureSA working bee -- unfortunately, we used poor plastic and it leaked and had to be taken apart and made again with better plastic :-(. Not good.

 I built a second bed using exactly the same method, but larger. This one is 4 m by 2 m. The sides of this are made of some old timber I had lying around, and it doesn't actually go all the way to the clay -- I let the deep mulch around the bed hold in the builders' plastic. This one leaks a bit, so I can't fill it much with water. It could be that the mulch has punctured it, but I think the plastic had a few holes (it was kicking around in my dad's shed for years and has been moved back and forth) -- also I only used two layers again -- silly! Use at least 4 if you do this -- moving all the soil is hard work!
(There are some volunteer tomato plants in this bed that need to be moved ;-)

Results

The beds seem to work pretty well, and hardly use any water. We're putting all our water-loving plants in there (not tomatoes!)

Learnings

1. You really don't want leaks in the reservoir. Make sure the base (in particular) and the sides are smooth to avoid punctures, and that the plastic doesn't have holes. Use the thickest builders plastic, not the thin stuff you get at B------.
2. It's really important that the base of the reservoir, and the bed above it, is level. Use a spirit level for this
3. Don't shove a garden fork or stakes into these beds once they're done ;-)
4. Don't walk on them
5. I'd like to think that, when I build the next one, it'll have a concrete slab at the bottom and rendered brick walls, but I'll probably just hack it again...
6. The beds take a long time to fill, particuarly gravity fed. Always use a timer otherwise you will forget which defeats the purpose of the beds (saving water).

I think they're great and we will use them henceforth.