Wicking Bed 2.0 May 2017
Some of you may remember when I first posted about my experiments with a kiddie pool wicking bed way back when. Well, I wanted to take some time to update what I learned about using that bed and how I designed a new bed at our new house. That original wicking bed experiment can be found here:
Overall, I considered that kiddie pool Wicking 1.0 experiment a great success. There were a couple issues that came up though. The biggest issue was the water lost from evaporation at the surface. Because the kiddie pool was so shallow, the soil was consistently moist at the surface and over time developed salt deposits. Accumulating salt deposits is the #1 problem I think desert gardeners will face when using these wicking beds long term and designing in a solution to mitigate this over time is critical to long term viability. One thing that would have helped was deep mulch cover. Keeping that in mind, here is a step by step on how we built Wicking Bed 2.0.
First of all location, location, location. Our original kiddie pool wicking bed was situated with an eastern exposure - that is the ideal here in Phoenix. It got shade from a mature citrus tree after about 2 pm in the afternoon. Unfortunately, at our new house I wanted garden beds along the front of the house and that is a western exposure, so right off the bat we are starting at a disadvantage! If you have a choice - don't do that! That said, I think things are growing well in spite of the disadvantage. If you want to see step by step photos of how we created this bed, here is a google slides presentation with comments so you can walk through it with us! There were just too many photos to post in this blog.
Dan Drilling Hole for Outlet Pipe (2016)
In Slide #3 you can see the drainage hole is at the bottom of the bed (see below), not at the desired water level! That is a critical departure from the majority of descriptions you will read elsewhere online about wicking bed designs (and Colin Austin, the wicking bed guru in Australia insists this feature is not optional in our desert climate). The reason for this is that now I can create a variable depth water reservoir! Say I have an infestation of fire ants - I can adjust my drainage outflow pipe to the max position and flood the bed to drown the ants, then reset the pipe back to a lower level to drain. Not only have I fixed a pest problem without chemicals, but I have effectively dissolved the salts from the soil and can now flush them out of the system. If I want I can pipe this overflow water to another in ground garden bed and nothing is wasted in this effort.
Picture from this afternoon (5/27/2017) showing outlet pipe at angle
This garden is so incredibly water efficient! This last winter the rain I harvested in buckets from the front porch was enough to water that whole season! That bears repeating, this garden used no municipal water all winter - I love it! Now that it's spring transitioning to summer, the water use is up and I have to use the hose to fill the bed. Even still, not more than once a week, I've been topping it off. I haven't been measuring the exact amounts, but It's minimal. The other added benefit to using rainwater all winter is that there are no salts in the rainwater and so the winter watering schedule will also help prevent salt buildup.
One more thing to note about this design. In my email conversations with Colin Austin about adapting his wicking style bed for the desert, he insisted that the water reservoir be filled with vegetation - especially weeds - for the added nutrients as they break down. I was not sure about this - typically wicking beds I've seen online are using inert materials (like gravel) as a fill for the bottom half of the bed. But we went out on a limb and did as he suggested. The plants seem to be doing quite well. I think this year even better than last year! There was a little sign of yellowing on some leaves on some plants the first year - probably as the woody plants broke down using nitrogen in the process - but this year, things are looking even better. The level of the soil has dropped as the plant material is breaking down, but I've been topping off with good compost and continuing to plant. The only major downside I can see thus far with filling the bottom with plant material to decompose is that it does do under water and so is smells like a swamp. Not a desirable trait right next to the front door of your house. This was easily solved by wadding up plastic bags and shoving them down the two inlet pipes and the one outlet pipe to contain the fumes... Now a year later, it no longer smells of swamp. But I thought you all should know!
I think wicking beds have a place in the desert gardener's repertoire. Not every plant will want to grow in them (rosemary and lavender - I'm looking at you!) but overall, I've been very pleased with the ease of use, productivity and long term maintenance of these beds. I'd love to know if anyone else has tried them and what success/lessons learned you have experienced?