Thursday, November 26, 2015

Wicking beds

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.



5 comments:

  1. Hi Angus,

    The locals around here that use wicking beds swear by them so I'll be interested to hear how it plays out at your place. Out of interest, what did you fill the wicking bed soil with? You mentioned mulch, but I was wondering whether you planted plants directly into mulch? Also the other thing that I was wondering about was how are you going transplanting tomato seedlings this year? I'm struggling with that as the success rate is well below 50%. Fortunately, I grew masses of tomato seedlings, but still the heat has been very hard on those transplants. Have you got any tips for that?

    Nice to see that you are back blogging!

    Cheers. Chris

    ReplyDelete
  2. Hi Angus,

    Forgot to mention that the previous Earthgarden magazine mentioned something about a build up of salts in the soils of wicking beds, but I have no experience with them but thought that it might be worth mentioning to you for you to keep your eye on. The locals tell me that they use far less water than any other plant growing method.

    Cheers. Chris

    ReplyDelete
  3. Hey Angus,

    I think the thickness and number of layers of plastic is less important than what it's sitting on, and what's on top of it. I used two layers of 200um black builders plastic, from B....., but used a fair bit of sand to make a nice smooth curved layer for it to sit on, then put old carpet and cardboard down before adding any gravel etc. No leaks so far, about 12 months in. Certainly an amazing way to use very little water to have a very productive patch of ground though!

    Cheers, Greg

    ReplyDelete
  4. Hi Chris,

    I just used the soil I'd had in the bed before, which is a mixture of (slightly hydrophobic) sandy loam and compost. The mulch is surrounding the bed and providing support for the plastic at the bottom. I really should have drawn a diagram -- I'll do that for the next post.

    We've had very good success transplanting the tomatoes between 150mm and 300 mm tall. Better than 80% success. Not sure why you've had problems. We're fairly brutal with ours -- don't give them much water at all and the ground is (almost) bone dry...

    I'm mindful of your comments about salt -- will fill the wicking beds with rainwater as much as possible

    I've been reading your blog, though I've not been commenting. Glad to see you're keeping busy too ;-) New chook house looks awesome

    Cheers, Angus

    ReplyDelete
  5. Hi Greg,

    That's a fair point, however it's very hard to assess the plastic for damage before you fill it with water, which you can't really do until it's finished. If at that point you discover a leak, you need to dig out the whole thing (been there, done that, don't want to do it again ;-)

    I'm very happy with the beds' performance so far! How old is your bed?

    Cheers, Angus

    ReplyDelete

Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.