Monday, May 25, 2009

Constructing 18 Gal Self Watering Containers (SWC)

*Update 05.24.2010* I have learned from my 1st season experience and will be modifying for future SWCs. I highly suggest you visit Our Engineered Garden for a much better designed 18 Gal SWC. Also, a ton of knowledge can be learned from

I built one of the two Self Watering Containers (SWC) over the weekend. There are a plethora of tutorials online for assembling this DIY project. I am not sure which is the originator, but here are several links:

Homemade Self-Contained Gardening Systems
The EarthTainer™
Self Watering Container Instructions

Most of my understanding of how a SWC works developed from various Garden Web discussions that involved Ray Newstead (aka rnewste/Raybo): The Earthtainer.

For simplicity, I mostly followed the instructions from the pdf I downloaded by Garden Web member, Joe (aka jmalt31) here: Joe's Self Watering Container Instructions

I wanted to make two SWC, so I started with two 18-gallon totes. Some instructions say to use the bottom one of the totes for the shelf between the soil and the water chamber. I thought it was a waste of a tote, so I followed Josh Mandel’s instructions for “The Single Tub Design.”

Here are the materials I used for each SWC:

18-gallon Storage Totes with Lid
5 or 6-inch aquatic plant basket for ponds
10x12 inch basket for supports
24-inches 1½ or 2-inch pipe for fill tube
Landscape fabric
Plastic Solar Mulch or Black Plastic Garbage Bag
Zip Ties
Bag of Miracle Grow Potting Mix (not garden soil)
If Growing Tomatoes: Granulated Fertilizer and Epsom Salt

PVC pipes, zip ties, and solar mulch we had on hand. We found the Rubbermaid tubs at the dollar store for $5. The 5-inch pond basket was a problem. All we could find were the 10-inch square baskets at the big box stores. Some people use these, however while doing my research on SWC, I read on the Garden Web forum that Raybo’s early experimentation with the larger basket resulted in too much moisture in the potting mixture.

Raybo now recommends using the smaller 5 or 6-inch pond basket. We looked for this in several places and couldn’t find it. We didn’t want to drive back to the big box stores where we found the larger square baskets, so we ended up using a square Rubbermaid Take-a-Long container that we will be drilling small holes in it so it will retain soil, but let water in. The pond basket, or Rubbermaid take-along container in our situation will be the wicking chamber. It will be filled with potting mix and dip into the water reservoir section. This will wick water up into the soil.

Here are the materials that were used for this project:

The first step is removing the middle out of the lid to be used as the aeration shelf between the soil and the water chamber. Be careful not to cut through the edge of the lid, as this will be used to hold the plastic mulch to the top of the container later.

Cutting out the middle of the cover was a struggle, as I didn’t seem to have the right tools to cut easily through the tough plastic. Most instructions suggest using a sheet rock knife or scissors, but neither worked well for me. So I ended up drilling a starter hole through the plastic and using this small saw to get through:

I then trimmed the edges of the aeration shelf smaller so it would fit snugly into the tub. I traced the Rubbermaid Take-a-long container that will be used as our wicking chamber onto the aeration shelf and cut out an opening slightly smaller.

I put all the pieces of the SWC together to try to figure out the best way to support the aeration shelf. I really didn’t like the flimsiness of the aeration shelf nor the rough way it fit into the tub and fully understood why they two tote method would probably be an easier method to assemble. Yes, it’s another $5 tote, but the alternative plan is to cut four 4-inch high PVC supports for the four corners of the aeration shelf. This seemed like a lot of work. So I decided to use this $1.75 black basket in the bottom to help support the aeration screen instead.

I used the Rubbermaid container that I am using as a wicking basket as a guide and cut out a matching square in the black basket:

Drilled small holes to accommodate the zip ties in four corners of the wicking basket:

Drilled small holes in the wicking chamber:

Drilled larger holes in the aeration shelf about 1-inch apart for air exchange:

Before assembling all the pieces, I used the black support basket to measure the aeration shelf location on one of the short sides outside the tub. I then drilled a 1⁄4-inch overfill hole in the tub about 1⁄2-inch below the mark. When filling the SWC with water I will know when it is full when water comes out of this overfill hole. This will also ensure that there will be at least 1⁄2-inch of air circulation between the aeration shelf and the water reservoir:

Zip tied the wicking chamber to the black support basket:

Assembled all the pieces to be sure that everything was ok:

Zip tied the black support basket to the aeration shelf and reassembled the pieces:

Placed the watering tube in it's location, traced an outline, and cut out the hole for the tube:

Cut some landscape fabric to help keep the soil from dropping down into the water reservoir:

Cut holes for the water tube and the wicking basket:

Now it is time to add the potting mix and plant. I used Miracle Grow Potting Mix for my SWC as this was the highest recommended mix for SWC in the research I did. However, if you plan on building a number of SWCs, the cost of the Miracle Grow Potting Mix can get quite high. If you want to mix your own, the suggested ratios are 45% peat moss, 45% compost, 10% perlight, plus 2 cups of hydrated lime or dolomite. For tomatoes it is recommended that additional fertilizer and Epsom salt be added to the SFC. If you are planting other vegetables, you won’t have to add the supplemental fertilizer and Epsom Salt as the Miracle Grow potting mix will be sufficient.
It took about a bag and a half to fill one 18 gallon tub:

Mixed some Miracle Grow potting mix with water and added it to the wicking chamber:

At this point I would recommend that you place your SWC at the place it will permanently reside, as it will be too heavy to move after adding the potting mix.

Added the rest of the Miracle Grow potting mix to the SWC 3-inches at a time saturating each layer with water until SWC is full. This is important as dry potting mix will not wick water and moisten the plant’s roots.

For tomatoes it is recommended that additional fertilizer and Epsom salt be added to the SFC. If you are planting other vegetables, you won’t have to add the supplemental fertilizer and Epsom Salt as the Miracle Grow potting mix will be sufficient.

I dug a trench in the soil across the middle of the SWC, and sprinkled a handful of dry fertilizer and a handful of Epsom Salt along the trench. Then I covered this lightly with the potting mix and watered in. Do not mix the fertilizer into the potting mix or spread it around. Also, do not use fertilizer that requires mixing with water, such as Miracle Grow or other generic "blue water" brands as these will not work for the SWC.

Once the SWC is full of moistened potting mix, lay the plastic solar mulch or black garbage bag over the top. The mulch will hold in moisture in the SWC. Snap on the cover:

Cut an X for the PVC water pipe:

Cut Xs for the plants. I am planting two tomato plants in each SWC, so I will mark the placement of the plants by cutting an X into the solar mulch where the tomatoes will be planted in opposite corners of the SWC:

Planting the tomato plants. Be careful not to disturb the fertilizer strip:

Adding the growing supports:

Trimming the plastic mulch:

Adding cedar mulch:

Watering through the fill hole until water comes out the overfill hole:

One SWC completed, another to go. I hope my tomato plants grow really well as this seemed like a lot of work. Maybe a project best completed during the winter when working in the garden is months away.


  1. Your step-by-step pictures and information are great! You have me all excited about making some SWCs now (I'll be making mine with 5gal. buckets)...

  2. Thank you Momma S. I have added more to the post since you read it. I was so tired last night when I was posting this that I had to stop and finish up today.

    The tubs were a LOT of work. I bet the 5-gallon buckets will be much easier and still function the same way. If I construct any more, I will go that route.

  3. Wow. Great post! Greetings from Wyoming!

    I want to try SWCs next year. I'm going to link to your post on my blog so that I'll be able to refer to your awesome detailed post... and share it with anyone else who might want to try them.

    PS... I love Maine! My grandmother lived in Woodland (now called Bailey Ville... I think) when I was growing up. I have found memories of spending time in that little town and of the wonderful adventures traveling from MA to ME! Sigh...

  4. Hey thanks Toni (WyomingMom)! I am glad you found this useful.

    I had to look up Woodland/Baileyville, Maine as it didn't sound familiar to me. I found it is up north near the Canadian border. Must have been quite a road trip from there to MA :),_Maine
    Originally settled by Quakers, how interesting!

  5. What a great post...I want to make one of these!Maybe next year- I think I found it bit too late!

  6. i have a few question.. i am so little bit confuess. you said 45 percent of compost and 10 percent perlite. how many cup of 45 percent of compost?
    second question is can i use mix of tomaoto and epsom salt put into soil i want to know what size of pour of tomato and salt too? what is about sweet pepper? is that same way like pepper ferilizer and salt too?

    pls email me

  7. Wow, this is one the most detailed explanations I've read for any home process. Well done. The exact description will help anyone who wishes to build such a system in his house

  8. I built several of these SWC containers last year. This year I decided to abandon that concept in favor of Larry Halls self watering rain gutter system. Check them out on YouTube. I built six this year and was impressed with ease of construction.

    1. Thank you for your comment. It has been several years since I constructed these SWCs. I have made some adjustments over the years and now only use two units for growing lettuce. I had not heard of Larry Hall's rain gutter system. I watched a video and it seems very interesting. Thanks for sharing.