Building a wicking bed for schools

Choose and Prepare the Site

Try find a position that gets at least 6 hours of sunlight per day in winter (e.g. North facing), with easy access and near a tap. Make sure the ground is level, not sloping. Avoid windy areas or ‘wind-tunnels’.

Smooth the desired site. Remove sharp objects and/or use carpet or sand to ensure nothing will penetrate the liner. If nut grass is present, place a metal sheet under the bed.

Picking Your Bed Size

There are two bed sizes appropriate for schools:

• Wide beds: 1,200mm x 1,200mm, allows access from all four sides.
• Narrow beds: 1,200mm x 600mm, allows smaller children easier access to the middle without having to lean across the bed.

Materials and Equipment

Frames

The timber allowed by the Queensland Education Department is Micro PRO Sienna treated pine. It comes in planks 2,400mm x 200mm x 50mm. Request the seller to cut the planks to length for ease of transport.

• Wide beds need 4 planks (all cut to 1,200mm)
• Narrow beds 3 planks (2 cut to 1,200mm; one cut to 4 x 600mm).

Joint Covers

ACQ treated decking timber is used to cover the joints and provide extra rigidity. Both sizes need 4 lengths 400mm long x 90mm wide. (Just visible at the corners.)

Liner Protector

H3 treated 75mm x 16mm pine fence pailings to protect the top of the liner from the sun and little fingers, and make the bed look tidy. These are placed last, after the liner is in position.

• Wide beds need 2 lengths of 1,300mm and 2 of 1,100mm.
• Narrow beds need 2 lengths of 1,300mm and 2 of 550mm.

Liner

Concrete underlay AS 2870 comes as a double layer of 200-micron (0.2mm) on 2,000mm wide rolls. Use it as double layer for ease of cutting and for extra thickness. It needs to cover the floor and the four sides.

• Wide beds need a single piece of 2,000mm x 1,900mm
• Narrow beds one of 2,000mm x 1,000mm.

90mm PVC Drainpipe and Fittings

• Wide beds: 2 lengths of 500mm, one of 900mm and one of 1,000mm, three elbows, one end cap and one screen cap (to stop mosquitoes).
• Narrow beds: 1 length of 500mm and one of 900m, one elbow, one end cap and a screen cap (to stop mosquitoes).

All beds:

• One tank outlet, as used for metal water tanks.
• 180mm length of 12mm poly pipe for the inside of the bed.
• 30mm length of 12mm poly pipe for the outside of the bed.

Fasteners

• 16 Batten screws size 18-8x100mm
• 32 Batten screws size 10-8 x 40mm.
• 30mm nails or screws as needed to nail/screw the liner protector in place.

Tools

• A piece of lino with one straight edge, a pencil, and an elastic band (to mark the pipes for cutting).
• A hacksaw (to cut the PVC pipes).
• An electric drill
• 60mm hole-saw (to cut the drainage holes in the PVC pipe)
• 22mm drill bit (to cut the outlet hole in the timber)
• 12mm drill bit (to cut a hole in the PVC pipe)
• 6mm drill bit (to pre-drill holes for the screws when assembling the timber frame).
• A small pair of pliers (to remove the cut-out bits from the hole-saw).
• A screwdriver (to put the frame together).
• A flat sander (to remove sharp edges, smooth the liner protector, ensure it is splinter-safe and for the bed to look good).
• A rats-tail file (to widen the 12 mm outlet hole in the fill-pipe to 13mm).
• A pair of scissors (to cut the liner).
• A pair of nail scissors (to cut the outlet hole in the liner).
• Clamps or masking tape (to hold the liner in place while filling the bed with soil).

Building the Bed

Once you have collected all the necessary materials and equipment you can begin to get started constructing your bed. Make sure to read through the steps first to ensure you understand where everything will go and consider laying everything out first before starting. Measure twice cut once to ensure that you don’t waste anything or make any easily catchable mistakes.

Cutting the Pipes for the Water Storage

1. Measure and mark the lengths of PVC pipe.
   • Wide bed: 1 of 1,000mm; 1 of 900mm, 2 of 500mm.
   • Narrow bed: 1 of 900mm, 1 of 500mm.
     The cuts need to be straight. Cut with a drop saw if available.
2. If cutting by hand, mark the line as shown in the photo by wrapping the piece of lino around the pipe at the marked distance and mark the circle. When cutting along the line, role the pipe towards you.
3. Mark the centres for the 60mm holes on the long lengths. Centre the first hole 150mm from one end, then the other holes 300mm apart. Pliers may be needed to ease the cut-out bits from the hole-saw.

Preparing the Liner

On a flat, clean surface, fold the underlay inwards 400mm along two opposite sides and 450mm along the other two sides to fit the bed floor area. Folding it first makes placing the liner much easier.

Preparing the Overflow

Cut a 45-degree angle at one end of the 180mm length of the poly pipe. When inserting the angled end into the overflow hole make sure the cut is facing down to prevent it intercepting water when filling the bed.

Putting it All together

With all your materials cut in place its time to put everything together. Once again check to make sure everything is cut correctly and lay everything out so you know where everything will go

Assembling the Frame

1. Place the first four timber lengths on a level surface with the inside frame measures up correctly
   • 1,200mm x 1,100mm for a wide bed
   • 1,200mm x 500mm for a narrow bed.
2. Pre-drill the screw holes, two per log, and screw together.
3. Place the second row of timber lengths on top of the first, and screw together.
4. Screw the vertical 400mm x 90mm pieces at each end of the long sides to provide rigidity across the joints.
5. Drill a 22mm outlet hole through the timber on the side closest to the inlet pipe (where the infill the beds with water). Centre the hole 140mm horizontally from the inside corner and 110mm vertically from the bottom.

Assembling the Water Storage

1. Place an elbow at each end of the one 500mm length which is the fill pipe.
2. Drill a 12mm hole in the elbow of the fill pipe for the overflow drainpipe. Centre this 95mm above ground level. Use the rats-tail file to widen it to get a tight fit.
3. Connect this pipe/elbow vertically to the 900mm pipe.
4. Connect the PVC pipes.
   • Wide bed: Arrange the pipes in the base into a U shape as shown in the photo above with one end connected to the fill pipe.
   • Narrow bed: join the 500mm fill pipe and 900mm length.
     Make sure the holes in the pipes are facing down.
5. Place the end cap.
   • Wide bed: Place on the 1,000mm length of pipe, at the opposite end to the first hole
   • Narrow bed: Place at one end of the 900mm length.
6. Place the mosquito screen cap.

Fitting the Liner and Overflow

1. Place the folded liner inside the fame and use clamps or masking tape to hold it up against the sides. Fold any excess over the top of the timber.
2. Remove the nut and the O-rings from the tank outlet. (The O-rings are not needed.) Push the outlet through the hole in the wooden frame from the outside and mark the centre of a 23mm hole on the liner.
3. Use nail scissors to cut the hole in the liner.
4. Push the tank outlet through the liner and screw the nut on the inside of the frame. (It’s easiest to tighten the outlet from the outside.)
5. Place the watering system in the bed.
6. Push the square end of the poly pipe onto the tank outlet and the angled end into the inlet hole in the pipe with the cut facing downwards.
7. Insert the 30mm poly pipe from the outside to keep out-flowing excess water away from the timber.

Installing the Liner Protector

Nail or screw the four lengths of the top liner protector in place. Sand any sharp edges and smooth the surface to protect against splinters and cuts. Make sure to sand in a well ventilated area.

Adding the Soil

Your bed is ready to fill. If you already grow vegetables, use soil from your existing beds. If you have to buy soil, see the Soils for wicking boxes and tubs for how to prepare good soil for best growth.

Happy growing – may you and your pupils have lots of fun growing and eating healthy food.

Written by Peter Van Beek – August 2024 (Version 2)