Build a self-watering raised bed from treated pine to grow salad greens.
Everyone loves to grow fresh salad greens, tomatoes and herbs. But backyard crops need regular water to thrive. Too much or too little can result in problems like rot, wilt and split fruit.
A weekend away can be enough to kill off a thriving vegie patch if there’s no-one around to do the watering.
To avoid the problem of withered crops, build these self-watering timber planters and use them to grow edibles.
Not only do they look good, but they also keep animals at bay and you can leave them for weeks on end without having to worry about water.
How they work
These self-watering planters are also called sub-irrigated planters, or SIPS, because they allow the plants to sip water whenever they want.
Built as a box with posts and a floor attached to joists, the timber used is MGP10, F7, H3 treated pine, as it’s long lasting for outdoor use in exposed situations above ground.
Cut lengths of 70 x 35mm timber in half using a circular saw and fence guide to make the posts.
When the box is ready, add a pond liner to retain water, then position the socked agricultural pipe and fill with soil mix. The secret to the success of these raised beds lies in the use of the socked agricultural pipe.
Once you fill the agricultural pipe reservoirs, they allow air to circulate and water to wick up to the roots of the plants whenever needed.
Watering plants from below means the roots stay moist and there’s less evaporation, so you don’t need to water as much.
TIP The clear plastic tube allows any overflow water to drain away.
Here are the top reasons to build a planter box for growing edibles.
1. It saves your back and knees.
2. You’ll have fewer weeds.
3. The simple sub-irrigation system saves water.
4. Have fresh food year-round.
5. You can create the soil mix.
6. Crops are safer from animals.
7. It can go in a yard or on a deck.
Planting a raised bed
To set up and maintain the raised garden bed, follow these guidelines. And for more great ideas on using sub-irrigated planters (SIPS), visit Inside Urban Green.
CHOOSE a spot that gets at least six hours of sun each day. If a planter is against a wall, you can get by with less sun because of reflected heat.
LINE the planter with a rubber pond liner to prolong the life of the treated pine and prevent chemicals leaching into the soil.
USE a light, fluffy soil mix that retains moisture without becoming compacted or waterlogged. Improve the soil mix with perlite. It forms spaces so water moves freely through the root system.
MULCH the planters to keep weeds down and slow evaporation.
TIP Perlite is ideal for use in propagation, hydroponics and container gardens.
How to build a self-watering timber planter
Position the end boards on a level workbench, aligning them with the corner to keep the assembly square. Lay three posts across the boards, one on each end and one in the centre, securing each post with two screws into each board.
Position and clamp the side boards on a level workbench, aligning them with the corner to keep the assembly square. Mark the post locations at 600 and 1200mm from one end. Position and secure each post with two screws into each board.
Stand up the ends and sides on a level surface and align the corners, positioning the ends in between the sides. Clamp each corner and measure the diagonals to check for square, then secure the corner posts to the sides using screws.
Cut a timber block to 340mm long to use as a flooring depth guide. Position the block against the side of each post inside the box and mark the top of each joist and floor cleat on the sides of the posts using a carpenter’s pencil.
Attach the floor cleats to the end posts then secure the joists to the side posts using screws. Position the floor boards hard against the posts and mark the notches to be cut out with a jigsaw. Lay the flooring and secure to the joists with decking screws.
Lay the pond liner inside the box, smoothing it across the floor. Fold the liner neatly at the corners and secure it around the inside top of the box using staples. Trim off any excess liner flush with the top of the box using scissors or a utility knife.
Secure the capping with screws, then evenly space three lengths of agricultural pipe in the box. Wedge the ends tightly against the box and pack soil mix around the pipes to keep them straight. Cut a hole at one end of an outside pipe for the PVC filler tube.
Drill a 12mm diameter hole in the end of the planter box opposite the filler tube just above the height
of the agricultural pipe. Cut a hole in the top of the pipe next to the box hole and position 12mm tubing from the agricultural pipe to the drainage hole.
Blend soil in a wheelbarrow to make a lightweight mix. Shovel the soil into the planter, finishing 25mm below the capping, then fill the pipes with water until it overflows. Add
the plants and mulch, giving the soil surface an initial water.