Steps
Step 1
Make sure you choose the right materials for the job. If you plan on growing edibles or will be in regular contact with the timber, make sure it is safe. Use new, untreated hardwood (reclaimed railway sleepers can be chemical saturated) or use pine that has been treated with ACQ or Micropro. Do not use conventional CCA treated pine.
For our project, we used one row of treated pine sleepers to create a 200mm high bed. Pine sleepers are the perfect choice as they are affordable and easy to work with.
Typically a bed like this would use sleepers cut-to-size for the posts but we decided to make it even easier by using galvanised pre-formed sleeper supports. These allow a sleeper to be dropped in and securely held. They are the fastest and easiest way to build beds and walls.
Step 2
Next step is to ensure your new garden bed is in the right position. Your bed isn’t something you will want to pull up and move, so take the time to get the position right. If growing vegetables or other sun-loving plants, select a location that provides maximum sun exposure across the seasons. Think about exposure to prevailing winds, too. You can position your bed in a sloping section of your yard, but this means it moves from being simply a raised bed to functioning like retaining wall on the downhill side. In this situation there will be a little extra work in securing the front posts. Finally, remember that the bed will become a fixed part of the landscape, so make sure it’s going to work aesthetically with the rest of your yard and not like an after-thought.
Step 3
Mark for the long corners on one side. You can do this by just laying a sleeper on the ground. Dig the first hole to around 200mm deep. Drop one corner-post into the hole with a maximum of 200mm above ground. Temporarily position a 2.4m sleeper in the slot of the corner-post to check alignment with the second hole. Add concrete to the hole, checking the post is plumb on the front and side as you do so. You can use the sleeper end to mark the spot for your second hole precisely. Remove the sleeper and dig the second post-hole.
Step 4
Position the second corner-post in the hole. Drop-in a full-length sleeper for spacing and alignment, and check the post is plumb. Put a spirit-level on the sleeper to check the level is correct before concreting the post in place.
Cut one 2.4m sleeper in half. Position one half sleeper in each corner-post. Measure from the inside corner created to the end of the opposite half sleeper and note the length. Reverse this and compare the lengths. This is called checking the diagonals. If they are the same then your sleepers are correctly positioned at a right-angle. If not, adjust until they are the same and then mark for holes on the ends. Excavate holes and repeat the process for corner-posts, checking diagonally again before concreting.
Step 5
Drop the final full-length sleeper into place between the posts. Work your way from corner-to-corner checking the sleeper height and add one fixing screw through the corner-post to each sleeper. Only add one at this stage to allow for adjustment at the other end. Once each is set at correct height and secured with one screw, go back around and add a second to lock them in place. You may find it easier to pre-drill the steel before sinking screw in.
Step 6
Cut weed-mat into strips around 400mm wide and to suitable lengths for each side. Lap these around two-thirds of the way up the sides of the bed and use a staple gun to secure. This will stop any soil from moving out beneath the sleepers and prevent grass from running into the bed.
Step 7
Find the centre of the long sides of the bed and mark each side at that point. Measure the distance between the inside faces. It should a little over 1200mm. Check the distance on one end to make sure the centre has not bowed. Cut the remaining sleeper to suit the distance. This is fixed from side-to-side across centre with 100mm screws as a brace to prevent the long panels bowing outwards over time.
Step 8
Ensure the weed mat is fully extended into the bed, not tucked under itself, then start laying newspaper. Wet it slightly first in a bucket to prevent it blowing away as you work. Cover the entire base to at least eight sheets thick. This will be enough to supress any existing grass until it dies back. The paper will then compost down into the soil.
Step 9
Position the remaining sleeper as a ramp on the side of bed and then start wheelbarrowing in the soil. Level the soil as you go to help avoid air pockets. But avoid compacting excessively – just lightly tamp down.
Step 10
Plant your new garden bed. We used a selection of semi-advanced and seedling sized vegetables. If you are putting in any plants that require stakes as they grow, such as tomatoes, put the stakes in at planting time rather than hammering through roots later on. Water well then spread mulch before watering again. Your bed is now complete!
