Sub-irrigation is a phrase I only recently came across. I was familiar with self-watering pots, which a home gardener might have a couple of, and I knew of wicking beds, a type of garden bed which also works on the principle of watering from below. Sub-irrigation techniques hit a different niche. It’s separate from a main garden, as with a self-watering pot, but the production size is similar to wicking beds in that you’re looking at doing garden-bed size projects right up to commercial level.
The basic idea with all of these is that water can be drawn up or wicked up through the soil (to a height of around 30 cm), so putting water at the base means plants can get water as they need it. It’s a much more efficient way of watering because it helps avoid overwatering and also water loss down through the soil out of reach of the root zone. This means that some crops that struggle here in our dryer seasons, in particular strawberries or the Cucurbitae (squashes, cucumbers, melons), get the constant moisture they need without needing watering outside of allowed times under water restrictions. Most water restrictions aren’t set to allow home vegie gardening in summer as a typical vegie patch needs watering every two days over our hot months, not just twice a week, and still might not keep enough moisture around their roots during a heatwave. This is a way around that problem.
The sub-irrigation planter systems I’ve seen so far have been home-built and home-designed, and it’s an area ripe for fiddling with. Especially in the urban setting. Got no back yard but an odd space down the side of the house? Whole courtyard is paved and you want to keep it that way? Want to roof your patio with strawberry plants? All of these are feasible. Add a pump triggered by a float switch and watering becomes automatic. The systems are also portable or movable, so they can be shifted around if needed.
Here’s one made with rain gutters, and a whole bunch more with variations. The gutters are placed between two 2x4s, which support ten buckets sitting on top. I like this one on a rooftop in Mexico. The writer of that post talks about the difficulty in getting people to use a system like this effectively and not keep watering from above as they always have, which is an interesting issue. I’m personally more interested in the materials – any garden bed or pot material has a finite lifespan, especially when exposed to sunlight, constant moisture and soil chemical reactions. So I’d like to know what the lifespans of some of these gardens are. Many are being made with recycled or repurposed materials which will lower the installation cost noticeably, and that’s good, but it can lead to uncareful material choices just because something was “available”. For me something has to last long enough to be worth the time and effort of rebuilding it when it falls apart. But the construction of these systems seems straight forward enough – looks like it’s mostly done with just a drill – that maybe it’s not so much of an issue.