Materiels
2 liter bottles
potting soil
seeds
thick string or yarn (either cotton or poly seems to work)
Phillips screwdriver
hammer
sharp blade to cut the bottle

Instructions
Cut the bottle in half.


Use a Phillips screwdriver and a hammer to punch a hole in the center of the bottle cap.

Cut a length of yarn/string about 1'-1.5' long, double it over and tie a loop on one end.


Thread the yarn/string through the hole in the bottle cap so that the knot is on the inside of the cap.  This will act as a wick, drawing water up from the basin below and into the soil.  The plant will take only what it needs, so the soil moisture will be perfectly regulated.

Put the cap back on the bottle top and nest the top of the bottle in the base. As the plants grow and use up the water, you can just lift off the top to add more to the base instead of pouring it over the soil.  As the soil dries, water will be sucked up through the string into the pot.

Optional: Label your bottle so that you remember what you planted

Add potting soil and seeds

Water....

You need to water the soil from the top the first time in order to make sure that it is uniformly wet and that the string also is wet.  Otherwise the surface tension of the water will prevent the whole thing from working correctly.

Some Notes:

Instead of lifting the top off every time you want to water, try cutting a small (maybe 1 inch) hole in the side of the water container, not large enough to compromise the stability of the bottle, but large enough to fit the spout of your watering can in. Might also help the bottle breath and discourage mold build-up.

Use a nail instead of a screwdriver (to protect possible damage to the screwdriver) Or even use a small drill

Also, you can cut the bottom out of a somewhat smaller bottle and place it inside the top of the planter until the plants reach a couple of inches. It sort of acts as a mini greenhouse by keeping the humidity high which is critical for very young seedlings.

For plants intended to go outside into the garden, I would recommend ONLY using cotton string or other biodegradable things for the wicks.

I used the outgrown, (grungy!) shoelaces from my children, grandchildren, & hopefully, great grandchildren (if shoelaces are still used by that generation), for wicks. They really work well, & I reuse then year after year. I soak them in dish soap, & hand wash all after season’s use, & store them in my gardening bag.