
My self-watering planter is based on a design by Larry Hall for his
Self Watering Pop Bottle Garden.
I will be planting herbs to grow in my kitchen over the winter.
Many cooks who aren't into gardening avoid indoor herb gardens because of (legitimate) fears the plants will die from too much or not enough water. This little system solves the water worries and practically guarantees success as long as there is enough light.
Herbs need at least 5 hours of bright, full sunshine a day to stay healthy, and sometimes the low winter light just isn't enough. You can place your herbs in a south-facing window, but for the best results, place your herbs under fluorescent lights for 14 hours a day, with the lights 6 to 8 inches away from the tops of the plants.
Making The Planter
The first step to making my self-watering planter is to add holes to the 2-liter bottle for drainage and to improve the wicking action of the water. To make the holes in the plastic I melted them with a screwdriver that I heated on my stove burner. You could also use a soldering iron, or a drill.
Make 3 small holes around the top of the bottle through the threads where the cap normally screws on. This will help the water to wick up into the soil.
Add 3 holes around the bottle 3 or 4 inches from the top. These are needed if the planter will be outside to allow rain water to drain down into the tub to prevent water-logging the roots.
Now, cut off the bottom portion of the 2-liter bottle. You won't need the bottom for this project.
2 larger holes are needed in the lid of the tub. The large one will hold the 2-liter bottle, and the smaller one is for adding water when needed. Trace around the bottle and the bottle cap with a pen to mark the holes, then cut with a knife or scissors.
Finally, make small hole about 3 inches up from the bottom of the tub to allow excess water to drain out and prevent over-filling of the tub. To avoid spills, you may wish to omit this if your garden will only be kept indoors, however, you must then be careful not to overfill when adding water. Keep only about 3 inches of water in the tub.

While not absolutely required, it is recommended that the bottle and tub be painted. In addition to looking nice, painting the tub and bottle protects the plastic from sun damage, and prevents too much light from causing algae growth. I used Krylon Fusion spray paint for plastic.
I'd recommend, especially if you are making these for gifts, that you not spray the bottom of the tub with paint. I found that the bottom gets scratched way too easily. Since the bottom wouldn't get exposed to sunlight, it's ok to leave it unpainted, which would avoid scratching issues. (I haven't had any problems with the paint scratching anywhere else. The Fusion paint really does a good job.)
The top portion of the 2-liter bottle will be inside the tub so it is not necessary to paint that area of the bottle.

The final step is to cut a small square of non-woven polypropylene fabric such as that from a blue Walmart shopping bag or some landscape fabrics. Fasten this to the top of the bottle using a wire or zip tie. This will keep the potting mix and roots in the bottle yet will allow the water from the tub to be absorbed into the soil to water your plant.
Firmly push potting mix down into the top of the bottle before filling the rest and inserting your plant. This will allow the water to wick up into the bottle to water the plant.
Maintaining The Plants
The only maintenance required for this self-watering planter is to add water once a week or so, as needed, and to fertilize periodically. The plants will take only as much water as they need from the tub so they will never get water-logged, nor will they get too dry as long as you maintain the water level in the tub.
Fertilize your plants about once a month by adding Miracle-Gro All Purpose Water Soluble Plant Food to the water in the tub. Miracle-Gro and Jobe also make plant fertilizer spikes that you insert into the soil a few times a year. An excellent organic fertilizer is fish emulsion. These are all available at most garden centers.