A couple of years ago I built a small and simple self-watering system out of four recycled PVC pipes and plastic pots. It hangs on a very sunny wall and holds 39 pots, which I use to grow alpine strawberries, vegetable greens, leeks, larger seedlings and the likes.
How it works:
The pipes are laid horizontally and have large holes drilled in them to hold plastic pots. Long wicks (reaching halfway into the potting mix) are installed in each pot and absorb water from inside the polypipe. This allows the bottoms of pots to sit above water level, preventing anaerobic fermentation of the soil mix.
Space-saving. For those of us who have limited space (balconies or small gardens) it makes sense to go vertical.
Water saving. In a closed system with water coming directly into the root zone, the only evaporation comes from plant tissues, not from soil surface.
Self-watering. Depending on the size of the plants and the weather, sometimes the water lasts for several weeks. Pick up one of the pots weekly to check the water level and top it up through the pot-holding opening. You can also fertilise the plants at the same time by adding diluted worm juice or seaweed extract to the water (this is called fertigation).
No mosquitoes. There is no access to the water which prevents mosquitoes from breeding in the pipe.
No root disturbance when moving plants. Because each of them sits in its own pot, when you harvest or replace a plant you don’t disturb the roots of the neighbouring ones.
I’m sharing instructions on how to make such wicking polypipe system to encourage readers to grow food where space is at premium – on balconies, terraces and townhouses.
What you need:
- A length of PVC pipe* (water and sewage pipes are 100-150 mm in diameter, orange electrical PVC pipes come in sizes up to 225 mm)
- PVC caps to seal both ends of the pipe (and silicone sealant to do so)
- An electric drill and a drill bit with a hole cutter. For a 150 mm diameter pipe I used the 110 mm cutter size (which fits standard pots 140 mm wide) and 130 mm cutter for larger, non-standard pots
- A pencil and a ruler
- A small metal file or rough sandpaper
- A few palm-sized pieces of flyscreen
- Plastic pots (I source mine from a recycling box at a local garden centre)
- Offcuts of geotextile/agfabric or another dense, fluffy artificial fabric (polyester fleece or similar) to make water wicks. Simply cut the fabric into 25 cm by 3 cm stripes.
- Outdoor paint*.
- Materials for supporting frame – see instructions below
* I would suggest painting the pipes to protect the PVC from deteriorating in the sun.
- Cut the pipes to the desired length.
- Draw a straight line along the pipe and mark the centres of pot-holding holes on it (I drilled mine 160mm apart for 140 mm pots).
- With a normal drill bit, drill small openings in the marked spots – they will serve as anchors for the hole cutter.
- Using the pre-drilled holes, position the hole cutter and drill large holes.
- Using a file or sandpaper, smooth the edges of the holes.
- Place a pot in one of the holes and have a look into the pipe to check how deep the pot sits. This is to determine where to drill an overflow hole in the pipe end caps. The overflow should be about 5 mm below the bottom of the pots to avoid flooding the soil. Mark it on the cap.
- Drill the overflow hole (about 4-5 mm wide) in one of the end caps and cover it from inside with a glued-on small piece of flyscreen to create a mosquito barrier.
- Glue the caps with silicone to the ends of the pipe making sure the overflow sits in line with the pot holes.
- Paint the pipe.
I have seen metal angle brackets attached to walls and pipes hanging from balcony railings suspended on thick, galvanised wire bent to fit two pipes: a smaller one inside the balcony and a bigger one outside the railing.
Whatever frame you decide to build, make sure it can carry the combined weight of the pipe, as well as pots full of soil and water inside the pipe. My 150 cm polypipes can weight over 30 kg each when fully planted and filled with water. Don’t use guttering brackets unless your pipe is short as they will bend and collapse, not being designed to bear weight.
Push one or two wicks through pot bottom holes, so about 15-20 cm of fabric hangs down from the openings.
Add potting mix of your choice and fill each pot halfway up, making sure the wicks are stretched up through the soil (not just along the pot walls or squashed at the bottom).
Plant the pots, adding soil to the brim and water well.
Put them in the already installed polypipe, but leave one pot aside, so one opening is empty. Use it to fill the pipe with water until it reaches the overflow hole (this is also how you top up the pipe and add liquid fertilisers). Place the last pot in the last opening, sealing the system.