Update March 1, 2010: This is a later version that I would recommend. In addition to a simpler way to make the soil platform, wicking system and reservoir, it uses a fill pipe made from recycled water bottles.
Update May 21, 2009: The platform in this version is made from the cover that comes with the tote box. I used a different color lid so that you could see exactly how I cut it with a box cutter.
Most of the lids I've seen on the web were cut from the flat indented section. Note that I cut it right around the top edge of the cover.
If the tote box has a cover, this is how I would make the platform. I like it better than any of the other platform materials...and it's free.
The two objectives in designing this homemade sub-irrigated (aka self-watering) planter are ease of construction and low cost. I believe both objectives are met with this design. All you need is a pair of scissors and a tool to poke holes. You do not need DIY power tools and you could make it from recycled materials.
Essentially the same construction method for making this bucket planter insert was used to make this box planter with one significant difference. The larger area of the box platform needs support. The upside down deli containers do that. They could be any plastic containers such as yoghurt containers. You could also use aluminum soda cans. Recycling is good!
You could make the platform from window screen material (recycled if available) instead of the vinyl tiles. If additional support is needed, duct tape the edges of the platform to the sides of the container.
You can see that you can vary the height of the reservoir depending on the height of the recycled containers you use. You may also prefer to add one or two more soil wicks. These are decisions that are relative to your climate and water consumption.
This planter was made from a plastic tote box but the same method can be used to make a wooden box planter. All you need do is line the wood box with sheet plastic (called visqueen in the horticultural trade) before installing the wicking containers and platform.
There is no proprietary secret about how these sub-irrigated planters work. They all use a simple principle of physics called capillary action. It is a highly accurate and consistent method of irrigation. It is far more beneficial for plants than gravity fed top watering.
You can see capillary action at work as water rises in an ordinary household sponge or paper towel. An even better way to learn about it is to grow some plants in recycled pop bottle planters. The planters are clear and you can see it all happen as the plants grow.
In this design, the soil (potting mix) in the two corner deli containers acts like a sponge. The containers of potting mix wick the water in the reservoir up into the growing area of the planter. It’s that simple. Just remember to use potting mix, not soil mix and for sure do not use soil from the ground (dirt)
One very important factor to remember is that unlike animals plants have no brain. They do not have the ability to drink or not drink as an animal pet does.
There are many claims that you cannot over water plants in these sub-irrigated boxes. That is a factual mis-statement but is functionally true when growing vegetables in sunlight. The rate of photosynthesis is such that water is consumed at a very high rate making it very unlikely that you will over water.
Move the planter into low light or indoors and you will most definitely over water the plants if you constantly top off the reservoir. The plant will die from a lack of oxygen in the soil. It will drown.
This topping off practice encouraged by the erroneous term “self-watering” is why these planters have a less than positive reputation in the houseplant community. It isn’t the fault of the planter. It’s a problem of operator error due to widely published misinformation.
The best practice when using sub-irrigated planters is to test the soil moisture not just check the reservoir level. Do not rely on the widely recommended finger probe. It is tricky to learn and highly subject to error.
Use a soil probe to pull a sample from the bottom of the planter and squeeze it between your thumb and forefinger. Use this method and you will soon learn to discern various levels of soil moisture with a high degree of accuracy.
The key words of irrigation are consistency and even distribution of water throughout the soil and root system. Use sub-irrigation in adequate light and your plants will thrive.