In my experience, recycled pop bottle planters are the best way to learn about sub-irrigation (aka self-watering). Once you get the hang of it, capillary matting is another simple way to sub-irrigate using any watertight planter.
This American Society for Horticultural Science (ASHS) research report extols the benefits of capillary mats for retailers. I have been using capillary mat sub-irrigation in a slightly different way for many years. I call it the aquapad method.
Simply install a folded pad of polyester batting material at the bottom of any watertight cachepot be it plastic, ceramic, melamine or metal. I use Pellon Thermolam Plus, a 100% polyester washable fleece batting material widely available in fabric stores. I bought it at Wal-Mart. It works just as well as more expensive capillary matting.
Incidentally, you can even use aquapads with clay pots. First, make the clay pot watertight by plugging the drain hole with caulking material and spraying the inside with tree-wound paint.
Note that there are three components to this system: 1. a watertight cachepot to create a "reservoir, 2. the aquapad at the bottom to facilitate wicking (capillary action), 3. the plant in a plastic grow pot with holes at the bottom.
The plant in a grow pot sits inside the cachepot with the aquapad under it. A measured amount of water then rises by capillary action in a perfectly uniform distribution throughout the root system and soil mass.
A key is to success with aquapads is to measure the water rather than simply flooding the cachepot. Never add so much water that it rises all the way to the soil surface. The top 1/2" or so should always remain dry. If you have experience with clear pop bottle planters, you know that the primary root system is at the bottom of the container.
Contrary to all the fear mongering about root rot in standing water, you will not rot the roots if you measure the water.
The water will rise by capillary action as if you are pouring it upside down. It’s very simple to do without buying a special self-watering planter.
Watering by capillary action (sub-irrigation) will produce healthier plants because of even and consistent moisture in the soil. It eliminates the stress associated with uneven drench and drain watering.
This method saves water and your time. You will also avoid fungus gnats because the soil surface is always dry. Fungus gnats need moist surface soil to propagate.
Along with pop-bottle planters, aquapads are as simple a sub-irrigation watering method as you will find. Both aquapads and pop-bottle planters are green and sustainable. Use them and your houseplants will be too.