Building a Self-Watering Container

Today was supposed to be the ‘Water’ episode of my 90% Reduction Project update, but life is crazy. Still hiring and training for Sundrops, my mother-in-law is visiting, and I haven’t managed to even look at the water bills for the last year. So, a different post on water: building self-watering containers for gardening!


I found these tubs via Craigslist. Step 1: Get some tubs
I bought 26 50-gallon rubbermaid totes for $4 each from a company that was selling 1000 of them – they’d been used to breed worms to sell as food for pet lizards. Each self-watering container requires two tubs.


Measure twice…



Step 2: Determine the depth of the dirt vs. depth of water reservoir
What are you going to plant in these containers? Will you grow deep rooted plants or plants that need a lot of water (or both)? The book “Square Foot Gardening” talks about making containers with only 6 inches of soil – the carrots came out L-shaped, but grew fine.

…cut once.
One of the tubs needs to be watertight. The other tub is going to be cut down and used as the divider between the top section (planting soil) and bottom (water reservoir). Some of the tubs had cracks in the bottom, so I used those to create the dividers.
Find another use for the top ring.
I used it as garden bed edging.

I cut a large strip off the top, about 7 inches below the lip, which will create about equal-sized top and bottom sections.


Step 3: Making it fit
Take the bottom section and put it upside-down inside the whole tub.
Structural plastic in the way If it doesn’t fit, figure out why not. My tubs had this bit of structural plastic sticking out in each corner.
Cutting openings so the divider
will fit inside the other tub.
To make it fit, I had to cut out flaps from the divider so it would fit all the way down into the whole tub.

Now that we’ve tested the fit, take the divider back out – there’s much more to do.


Step 4: Drill time
Drill holes in the divider
Next we have to drill holes in the divider. ‘What good is a divider with holes?’, you ask? The divider needs three kinds of holes:

• LOTS of little holes for air exchange and drainage if it rains.
• A few bigger holes to hold a wick – a piece of cotton with one end in the water reservoir and the other end in the dirt. The wick allows plants to suck up into the dirt only as much water as they need.
• One hole to hold the access tube for adding water to the reservoir.

Holes in the sides too



I used a 1/4″ drill bit to make all of these holes, but making the larger holes is much easier if you have a hole-cutting drill bit. Drill air exchange / drainage holes every couple inches all over the bottom and sides of the divider. Make 3-4 slightly larger holes in the center, evenly spaced from end to end, by drilling 4-5 holes so close together that they merge. The large hole for adding water needs to be pretty big (the size of the watering tube – see step 5) and I got really tired of drilling this big hole with a small drill bit by the time I’d made a few of these containers.

Drill overflow hole through
both outer container and divider

One last hole to drill. Put the divider back inside the whole container and find where the top of the divider sits inside. Drill a hole through the side of the outer container and through the divider about 1 inch below the top of the divider. This is the overflow hole, to prevent your plants being drowned. When watering, you can just leave your hose on until water starts coming out this hole, and your water reservoir will be as full as it can be.

Hold pipe still using a C-clamp or vise
Cut pipe at an angle
Cut pipes for multiple containers
Step 5: Watering Pipe
Remember that big hole in the corner? Well, now we need to make the watering pipe that goes through that hole. Take a length of pipe (some people have argued against using PVC, but the leaching concern is really about phthalates used to make softer PVCs, not hard pipes, and I had it on hand) and clamp it to a table. This is going to be difficult, since the pipe is round. Keep trying until the pipe is steady.

Cut the pipe at about a 45° angle – it doesn’t need to be exact, the purpose is so that the pipe will never sit flush with the bottom of the container and keep water from flowing into the reservoir.
Pipe with bugscreen Step 6: Keep the bugs out (optional)
In my original version, I put bugscreen over the top of the watering pipe and the outflow hole in the side of the container to prevent mosquitoes laying eggs in there.
Screen covering outflow hole However, halfway through the first season the rubber bands broke and the bugscreen started to come off, and the outflow holes had a tendency to get clogged with soil. I didn’t use screen the following year and didn’t seem to have any insect problems.
Container with soil guards
Step 7: Keeping soil in place
Put the divider back in the whole tub, making sure the outflow holes line up. In my tubs, there was a considerable gap around the edges, and I didn’t want all my soil to fall down into the water reservoir, so I added little cardboard flaps to keep the soil out of the cracks. However, when I went and filled the tubs with soil, they tended to bow outwards, and soil still slipped down, obstructing the outflow hole in a couple tubs. I’m thinking I might try a few layers of newspaper around the edges next time.


Measuring the wick Step 8: Adding the wick
Get some cotton material – it can be an old T-shirt or whatever you have in the rag bin, I’m using some braided denim I made from old jeans back when I owned a laundromat and always had a huge pile of lost-and-found, and which had previously served as wrapping for a cat clawing tower. Make a knot in the middle of the material, making sure the wick is long enough to drag on the bottom of the container, and stuff the end down through the holes. The cotton will eventually break down, but mine last about a season just fine, and I replace them in the spring.


Fill with water, soil and plants! Step 9: Plant
And you’re done! Just put it where you want it to end up – it’s going to be heavy when full of water and damp soil. Then fill with water (it’s easier to fill it all up before the soil’s in place), add your soil, and you’re ready to plant!

Update Notes
I made this tutorial a year or two ago, and have found a couple problems.

• The containers I made are BIG and all that soil gets heavy. The divider bows down under the weight, and eventually cracks. This year I’m going to put a couple empty plastic pots that are about the right height in the water chamber to help hold up the weight.
• I’ve had a couple containers develop a crack in the bottom and start to leak, and since my containers are resting on landscaping rock I don’t necessarily notice right away. I’m going to epoxy the thin and cracked places this spring before replanting the containers this year.

Other Resources

• Incredible Vegetables from Self-Watering Containers: Using Ed’s Amazing POTS System, by Edward C. Smith – As always, I suggest borrowing it from the public library rather than (or at least before) purchasing.
• Homemade Self-Contained Gardening Systems – This is a different version, using a basket of soil in the water reservoir to bring water up to the plant roots, rather than a cotton wick.
• Pat Meadows – A description of self-watering containers, why you’d want to use them, and links to some other instructions for making them.
• Container Vegetable Gardening: Healthy Harvests from Small Spaces – A nice version made using 5 gallon buckets. I had made a couple using two nested buckets, but it didn’t provide a very deep water reservoir – this version allows you to place the divider wherever you want. I’m also considering stacking a smaller bucket (abt 4 gal?) inside a standard 5-6 gallon bucket to get a larger water reservoir. I can sometimes get empty 5 gallon pickle buckets from a nearby deli, and smaller peanut butter buckets from my local co-op.