A Life of Green: How to make a wicking bed

I'm part of a community group in Melbourne called Permablitz that does urban gardening and agriculture. Of the many cool things about Permablitz is the workshops they hold. I learned how to make a wicking bed system through Permablitz and next weekend, I'm going to be facilitating a wicking bed workshop at the next Permablitz. But before that, I wanted to share the notes on it.

So what is a wicker watering bed? It's essentially a raised garden bed where water is stored on the bottom. For gardens in hot weather, it's a good way to help keep water storage to the maximum and keep plants alive. The water is poured into a pipe that runs through the bottom of the bed and seeps into the scoria (volcanic rock) or sand or whatever sediment that you use for the bottom storage layer. By preventing water leakage with plastic inside the bed, water can be held. Plants can then draw up moisture from the bottom via capillary action, which is the same principle as growing seedlings on a tray of water.

You can also combine the wicking bed system with a worm farm system. This way, nutrients from the worm poop can steep into the water and the plants can take it up. A worm farm is also a great way to add in nutrients into the closed wicking bed system - since you're taking out the crops (and nutrients) from the bed, you have to add back in the nutrients somehow and the worm farm is an easy way to do this. See the last step if you want to combine the worm farm with the wicking bed.

Steps for making a wicker watering bed

Start with a raised garden bed or any container that you want to grow vegetables/plants in. You can have anything from a broccoli box to a full-on garden bed. The bottom scoria/sand layer needs to be about 5-10 cm and plants require 30-35 cm of soil (this may vary depending on what you're growing). If you have garden beds that come up to your waist, you can fill the bottom with wood pieces or carpet (note on carpet: just make sure the carpet isn't in direct contact with the soil/scoria as there is sometimes chemicals in the carpet). You can also use carpet/wood chips to make the bottom more even or cover up any parts that might tear holes into the plastic.
Using a sheet of plastic, line the sides and bottom of your garden bed. It's important that this plastic not have any holes, as any water leakage would defeat the purpose of the wicker bed. Although you don't necessarily need to line the sides all the way up, it makes it easier not to have the plastic slip down over time or weeds grow between the spaces of your plastic/soil and the garden bed container.
Measure out an appropriate length of agricultural pipe, which is basically tubing with holes on the side so water can drain out. In small garden beds, you can just lay the pipe out diagonally, but for larger beds, zigzag it. The pipe needs to go all the way up one side of the bed to where it'd be above or flush to the top of the soil. This is where you'll pour water into the pipe.
Once measured out, cut the piping and cover both ends with a piece of shade cloth or some other permeable material that will allow water through but prevent sediment.
Fill the bottom with a 10cm layer of scoria/sand, covering the piping. Use your feet to keep the piping in place as you pour in the sand. It's important to keep the sand layer even, otherwise the water will be biased towards one side, so use a balance to see if this layer is level. As you leveling, make sure not to tear holes in the plastic surrounding the bed. Once level, dig out ridges in the sand (see below) so that even if the water level drops, the soil can always be in contact with the water.
IMPORTANT: Once you have your sand layer in, an outlet must be placed in. This is so that you can tell when you've added too much water to your wicker bed. If too much water gets into the bed, it gets swampy and acidic, which is not good for the soil. To prevent this, make an opening in your garden bed where the top of your sand layer is and place a small PVC pipe (~25mm radius) through to the outside. This way, if the water level goes above 10cm, then the overflow can leave the bed via the PVC pipe. Cover the end of the PVC pipe that's in the bed with shade cloth/equivalent to prevent sediment from clogging it.
Once your piping and sand layer is done, place another layer of shade cloth over the whole bed. The soil layers will sit on top of the shade cloth. The benefit of this is that you can periodically lift up the entire shade cloth and do maintenance on the bottom sand layer if necessary. The shade cloth should go all the way up the sides of the garden bed and over the top a bit. IMPORTANT: Make sure the shade cloth is as flush as you can get to the sides of the bed because anything that falls between the sides will contaminate the water in the sand layer.
Start layering on soil, manure, and dynamic lifter to the top of the garden bed. You can pretty much put whatever you have on hand, but for nutrient rich soil for plants to grow in, it's best to layer in sheep/horse manure (best for leafy vegetables) or chicken manure (high in phosphates, good for food producing plants). Other things to consider - straw, dynamic lifter plant food. Keep sandwiching different layers in until you hit about 5cm to the top of the bed.

WORM FARM: An easy way to add nutrients to the wicking bed (a closed system) is to have several worm farms along the sides of the bed. Simply take a plastic bin (such as an old ice cream tub), cut out the bottom, and place against the side of the bed and on the bottom of the shade cloth. This way, the worm droppings will steep into the water and be diluted enough for plant uptake. You can have as many as you want, depending on how big your garden bed is. As you layer in the soil and the manure in the bed, fill around the bin to secure the placement. To activate the worm farm, fill it with straw/moistened cardboard, or newspaper at the bottom and worms. On top of that, place your kitchen scraps (vegetable peelings, uneaten leftovers, coffee grinds, tea leaves, etc). Eggshells can be used, but since they're harder to decompose, crush them first. Avoid citrus or onion peels because they're acidic and worms don't like them. Keep this worm farm covered to keep in the moisture.