This inexpensive DIY project makes starting or growing plants a whole lot easier by automatically keeping the soil at just the right moisture level. All you need is a 2 liter bottle and some string.
ASBloom shows you how to make these clever planters on the Skruben blog. Basically, you cut the bottle in half, and thread some string or yarn through the bottle cap. Then invert the top half into the base and add your plants and soil.
The yarn acts as a wick and the plants will take the water as they need it. Even better for those of us with black thumbs: The clear bottles help you see when the water needs refilling.
(Note: If you need a larger planter, you can instead use a milk jug and some foam for your automatic watering needs.)