A self-watering window box is window box that has a mechanism of watering itself for some duration of time. Many companies now offer a self-watering option as a way to reduce the time and frequency of watering and thereby lowering the overall maintenance needed to water a window box.
In the window box industry there are basically two ways in which to make a window box self-watering. Method 1 is drip irrigation and method 2 is self-watering reservoir system.
Method 1: Drip Irrigation
Drip irrigation is the use of a water line or hose that is continuously fed water at a slow rate and into the window box. Most drip irrigation methods are truely self-watering in the sense that they are either automatic or on a timer. This makes them have a very low maintenance schedule. The line is typically fed to the box from an outdoor spigot set that is barely turned on. The hose is then ran along the ground or wall to the window box where it is spliced and several drippers are connected to the house. The purpose of the drippers is to slowly drip water into the top of the box. Usually a dripper will be placed every 12" of window box length.
Sometimes a dripper is on a timer and sometimes the drip system is tied into the sprinkler system so that every time the sprinklers are turned on water is fed to a pipe or hose that then drips in the box. The disadvantage to a drip system is that there are typically visible irrigation lines running to the box that may be unattractive. This can be problematic, especially if the window box is high up on a second window and usually this is a deal breaker for people who don't want an unattractive sight climbing the house to get to the window.
Method 2: Self-Watering Reservoir
An enclose reservoir system for a window box has many advantages that a drip line don't have but also some disadvantages. First off, an enclosed reservoir system is usually a container of sorts that is placed on the bottom of the box and covered in soil so that it is not visible. Most of these containers are there so that you can overfill the window box with extra water and the system can figure out how to deliver the water to the plants and soil at the correct time as it dries out.
Usually a self watering system involves the use of wicking water vertically to the soil as it dries. These systems usually require the use of potting mix rather than soil or potting soil due to the nature tat potting mix is a good wicking medium for water to climb.
So what makes these systems self-watering? They are usually this way because you can put much more water in the window box and water less frequently. One such self watering window box system with FlowerWindowBoxes.com does just that. You water the soil first, then you fill up the reservoir afterwards by pouring water down a vertical pipe that is off in the corner. The combined effect of watering and filling the reservoir allows for the window box to have 3 times as much water in the box. As the potting mix dries out it will then wick water out of the reservoir system and feed itself. It is not uncommon for setups like this to result in watering a window box once a week instead of three times a week. And it makes watering easier, especially if you have to go on vacation for a week.
About the Author
Matthew Buquoi is the owner of Flower Window Boxes and inventor of the Self-Watering Window Box Wick Tube.