How To: Self-Watering Seed Starter Pots

I've tried starting seeds indoors several different ways over the years.  So far this is my favorite method because the soil is always exactly the right moisture level and it's very easy to see with the naked eye when it's time to add water to the planter.  There's no guesswork involved and the plants seem to love it.

Here's how we made them:

You need 2 liter bottles, potting soil, seeds, thick string or yarn (either cotton or poly seems to work), a Phillips screwdriver, hammer, and a sharp blade to cut the bottle.

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.

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.

...and wait.

Ahhhhh.  Spring!

A note to all readers:

I've had lots of great comments and questions about this post, many of which I'm not able to answer myself because I just don't have the broad range of knowledge about plants that is necessary.  If you do have that knowledge, please feel free to jump on board the comments string with your input.  It would be greatly appreciated!  

Also, we have moved this post over (Jan, 2014) from our previous blog platform, and were unable to bring all of the excellent comments with it, so we are including a few here...

• Anonymous said...Place a block of wood under the cap when punching the hole or you will end up with a splintered deck/floor.
• Anonymous said...I use 1 quart Gatorade bottles and do the same thing. If you threw out the lid it's no big thing, use several cotton balls or a bunched up piece of paper towel, or cotton fabric, or even a piece of sponge to act as an absorber and clog the hole.
• Anne said...I also had been thinking about using an unbleached coffee filter inside the bottle, to hold the soil. This would help the moisture to wick evenly and it would make it very easy to remove the plants if you plan to transplant them into the garden at a later date. I haven't tried it yet though.
• @Jenny...The first time I water them from the top so that the soil gets a good dose of wetness. After that, I lift the top part (with the plant in it) up and pour an inch or two of water into the bottom. As long as the soil didn't completely dry back out, the water will be sucked up into the pot from below. If the soil dries out too much, it breaks the surface tension bond of the water and inhibits capillary action (which is why the whole thing works in the first place), so you would need to water from the top again. Does that make sense? Sorry for the wordy explanation.
• @Anonymous...I only add water when I see that it's close to empty in the bottom basin (every four to seven days, depending on the size of the plant). I try to never let it dry out completely. I bet this method would work well for you, even if you only water once a week. You could cut the bottle so that the lower portion was actually larger (say 70% instead of 50%) and would hold more water wile you're away.
• Anonymous said...For those who have discarded the lids, you can always use a small square of old screen to block the hole, yet water through.
• Unknown said...Don't use a screwdriver. If you want to punch it, then buy a awl or a hole punch or even use a small drill. Using a Philips head to punch the hole will probably ruin the screwdriver. Other then that: great idea.
• Anonymous said...This is a great idea! Family has been thinking about building a greenhouse - wow! this will be so much more economical. Especially since I have a sun room. I use the "wicking" system for my outdoor plants in the opposite way. No plant wants to have soggy roots all the time, so after a big rain I lay a piece of string/rope in the saucers leaving the other end on the ground so it will drain my saucers.
• Mary G said...For plants intended to go outside into the garden, I would recommend ONLY using cotton string or other biodegradable things for the wicks. You don't want to end up with a bunch of nylon/polyester strings in your soil. Yuck! LOL I also love the idea of using the tops of other bottles to create a mini-greenhouse for increasing the humidity. Ya'll are a bunch of geniuses! =)
• Anonymous said...Agree re using an awl vs a screwdriver. The screwdriver may look fine (although I would be livid if someone used mine like that!!), but the top of it is not designed to be impacted that way, and may chip off. Better to use a hot nail, a cold nail with a hammer (an surface protection if you're working on a marrable surface (or concrete which is also dangerous to work on with impact tools and no safety gear), or an awl.
• Anonymous said...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.
• Backyard Farming in Michigan said...A drill works much better for the caps. 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.
• Anonymous said...Just found this site today on fb, GREAT idea to start seedlings! Another use I have found for 2L pop bottles is to "plant" them upside down in the garden right beside the tomato plants...minus the bottle caps and with the bottom cut out, leaving some of the bottle up out of the ground. Filling the bottle with water allows the water to get to the root zone of the transplant; I tried some with and some without-huge difference in growth and health of the plants. This way there's no danger of soil fungus splashing up onto the leaves and eventually ruining the crop.

Please continue to add to the discussion!!