How to build a wicking garden bed

[Adam_W]

Difficulty: Intermediate

Wicking garden beds use less water and keep soil moisture at the right level for optimum plant growth. They are a favourite of vegetable gardeners but can also be used for regular garden plants and are easy to create.

We’ll be constructing a 2400mm x 1200mm x 500mm garden bed. 500mm is a standard depth for wicking beds as this depth allows for 100mm of gravel, 300 to 350mm of soil and then a layer of mulch. You can adjust the width and length to suit your needs, but stick to 500mm bed height.

Once you have levelled and prepared an area in your garden or sourced or built a suitable stand, you can get started on the build.

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Steps

Step 1

Check lengths of all sleepers. Sleepers will often be 5 to 10mm longer than their stated length and their end cuts may not be square. To keep your frames nice and square, first check lengths and square of all sleepers, then trim and square-up as needed before cutting your final lengths. Once you’ve done this, measure to 1200mm on two sleepers and cut to create 4 x 1200mm lengths.

Treat all your exposed cuts with Ecoseal tanalised timber treatment to restore their treatment.

Step 2

Position one full length sleeper and one 1200mm section so they are square and flush. Pre-drill to avoid splitting and screw together with the 125mm bugle screws to create a butt joint. Use three screws evenly spaced for each join and fasten through the face of the long boards into the end of the short. Repeat to create one box frame section.

Step 3

Repeat steps 1 and 2 to create the second box section. To help keep it square with the first section, assemble the frame in position on top of the first. Once complete, pre-drill at a steep angle from the top to bottom sections and use 100mm bugle screws to join. Use a minimum of two screws per side. If you are building your bed on a base then use this process to attach to the base too.

Step 4

Your final sleeper level only needs to be 100mm high. Measure the middle of two sleepers, set your power saw guide to suit and then saw, ripping the sleepers down from end to end. You’ll find it easier (and safer) to clamp your sleepers down to a bench or sawhorses. Remember to cut one section to 1200mm for the ends. Repeat step 3 to complete your frame walls.

Step 5

You will have one remaining 100mm x 2.4m section. Measure and rip this down to create two 50mm x 50mm lengths. Cut one length into four smaller 500mm sections. Once again, seal all cut ends with your treatment spray.

Position these in each corner and use 100mm bugle screws to fix to both sides to create internal corner braces.

Step 6

Determine the best side for the overflow fitting. Fit a spade bit or Speedbor to the drill and drill the hole so that the bottom of the hole will be just above the top of your slotted drainage pipe. You’ll find it easiest to just put the pipe against the wall and take the alignment from that.

Drill a hole in your preferred location for your drain outlet and tap. If fitting in a side wall you will need to cut down the flange on one side of your fitting to allow it to be installed as low as possible.

Step 7

Unfold the liner and position the middle of one long edge along the longest bed side. Staple in place around 50mm down from top edge with staples every 50mm or so. Now carefully unfold the liner, taking care not to pull against the staples while gently pushing into corners and covering all sides. The aim is to ensure there is no tension in any side or bottom corners. The liner must tuck all the way into the corners and be in contact with all surfaces.

You will need to make folds in the corners. You can staple off as you go. Once fully lined use a utility knife to trim the excess from the top edges.

Step 8

Locate holes drilled for outlets and carefully use a utility knife to cut a hole in the liner. Apply a bead of silicone to the back of flange on the internal part of the tank fitting, the one with the threaded pipe attached. Push through the hole and then screw nutted flange on from the outside. You may need to use a spanner to tighten but do not overtighten. For your tap, attach a ball valve tap fitting to the threaded pipe on the drain pipe.

Step 9

Lay slotted drainage pipe out in a loop inside bed base. Cut to make one loop with ends that meet. Now cut pipe into sections at the halfway point of each side. At each cut add a T-joiner. The joiners at the middle of the long sides should be lying flat. Point them upwards at the short ends of the bed. Cut and fit a short section of slotted pipe to connect to centre T-joiners across the width of the bed. Cut PVC pipe to 500mm lengths. Insert one section into each upward pointing T-joiner. Check these riser pipes are plumb and secure them in place with saddles and button screws.

To avoid puncturing the liner while it is exposed it is best to not wear shoes while working in bed.

Step 10

Gravel should first be rinsed to remove any silt. Do this by puncturing the base of the bag, opening the top and flushing water through. Carefully spread gravel, making sure that the slotted pipe remains sitting flush with the bed base while you do so. Fill until the slotted pipe is slightly covered, this should just reach the top of the overflow outlet.

Step 11

As there is a possibility that the long sides of your bed may bow, you need to add a cross brace. Cut 100 x 50 hardwood to give you two lengths of 400mm and one of suitable length to span from side-to-side internally. Position the shorter lengths directly opposite each other in the middle of the long sides of your bed. Ensure they are spanning all three side panel boards and are plumb, pre-drill and secure to side with 100mm screws. Put at least one screw into each of the three side panels. Position longer section across bed with the top around 150mm down from top of shorter lengths, clamp in place, check level, pre-drill and secure to other hardwood pieces with 100mm screws.

Step 12

Cover gravel with drainage fabric. It needs to lap about 50mm up the sides. Ensure there is no tension in the edges and corners, cut to fit and staple in place.

The bed can now be filled with soil. Bring soil to approximately 75mm below the top of the bed. The mix should be gently pressed down as you fill to avoid air pockets and the soil level later dropping through settling.

Step 13

Once filled with soil, you can plant out and mulch your new garden bed. When spreading mulch it should be around 50mm thick and ensure it is kept around 50mm all-round away from plant stems and trunks.

Water your bed thoroughly until you see water coming from the overflow outlet. The first couple of waterings should be done this way but once the plants are starting to establish, water by popping your hose into the riser pipe and running until water comes from the overflow.

Step 14

You don’t have to leave your bed as plain timber. Treated Pine can easily be painted, stained or even clad. We clad ours with Ekodeck Plus wide-slat composite decking boards using concealed fasteners.

Materials

• 8 sleepers H4 treated Pine 200mm x 50mm x 2400mm, preferably Microshades
• Bugle batten screws, Climacoat, pack of 100mm or 125mm and pack of 75mm
• 15mm or 20mm galvanised button head screws
• 1 piece of 100mm x 50mm x 2400mm hardwood
• 4m x 3m pond liner
• 1 roll of 50mm or 65mm Draincoil slotted drainage pipe
• 4 Draincoil T-joiners to suit pipe size
• 1 PVC pipe 1m to suit T-joiner size
• 4 pipe saddles to suit PVC pipe size
• 1 tank outlet flange 20mm (3/4”) – This is for overflow. If you wish to add a bed drainage outlet you will need 2 fittings to suit your situation.
• 20mm ball valve tap fitting if adding a bed drainage outlet – optional
• Filter or drainage fabric, at least enough to cover 2400mm x 1200mm
• Silicone sealant, full exterior-grade roof and gutter is best
• 6 bags of 20kg drainage gravel
• Garden mix, bagged or bulk, suitable for raised garden beds (or planter boxes if building a platform bed) approx. .8cu/m
• Mulch
• Ecoseal tanalised timber treatment.

Tools

• Battery drill
• Driver bits for all screws
• 20mm spade or Speedbor bit
• Drill bit for pre-drilling for bugle screws
• Power saw capable of cutting sleepers with guide
• Measuring tools – tape measure, long and short levels, carpenters/framing square
• Clamps
• Staple gun
• Utility knife
• Large spanner.

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