Harvesting vegetables successfully needs neither a big garden nor much work watering. In this blog post I describe how to build a planter with long-term irrigation out of a 30 l plastic container (a flower pot in this example), an onion planting tray, some fabric (from an old pair of jeans, for instance) and a garden fleece. A drill or a cordless screwdriver is a bonus, as it makes the drainage hole easier to make.
When choosing the plastic container, make sure there are no holes in the bottom (or seal them with epoxy resin). The onion planting tray goes into the pot upside down and should have roughly the same diameter as the pot.
The onion planting tray separates the water reservoir from the growing medium.
Now drill a hole (6 mm) in the side at the height of the onion planting tray. This acts as an overflow so the plant does not stand in water. The planter can later be filled with water up to this point. To draw the water up out of the reservoir I used strips of fabric from an old pair of trousers as a wick and hung them into the planting tray.
The two fabric strips carry the water up into the growing medium.
All that remains is a garden fleece, so the growing medium does not later fall into the water reservoir. It is worth pushing a plastic pipe cut off at an angle into the SIP for filling it with water later. It makes watering easier.
The garden fleece is the separating layer between the water supply and the growing medium.
Now the sub-irrigated planter can be planted up. Ordinary vegetable soil, fertilised occasionally, works fine as the medium. At the start, water the SIP normally (making sure the reservoir is always full) until the roots have developed and can draw water from below better. After that it is enough to fill the reservoir through a plastic pipe and a funnel. If it is not too hot, you only need to water every few days.
More on the subject at: Green Roof Growers: How To Make Two Bucket Sub Irrigation.