Simple Sub-irrigation Grow Box

 

This do-it-yourself sub-irrigated grow box (erroneously called self-watering in the retail market) is a configuration (photo below left) from the Rooftop Gardens Project in Montreal. I made it using only a box cutter except for using a drill motor to drill a drain hole in the side. You could easily make the hole with a hot poker if you don’t have a drill.

The material is expanded polystyrene panel foam insulation (often erroneously called Styrofoam) just like the tomato plant cell pack on the right. The panel foam came in a package of six (6) 3/4"x13 5/8"x48" "boards". That's enough to make six or more grow boxes of this size.

Note that the support grid forms 9 spaces. You can see that the 4 in the corners are left open. These are filled with tamped down potting mix and create 4 "soil wicks". The other 5 spaces under the support platform form the water reservoir. You simply add water through the fill tube until a small amount flows from the overflow drain hole and then you know the reservoir is full. 

 

The box is a 14 gallon, (23.9x15.9x12.2 in.) bronze Rubbermaid Roughneck tote box. The next time I would use the same type box only in the 18-gallon size (23.9x15.9x16 in). This would increase the water reservoir capacity. Keep in mind that this will also increase the overall weight when full.

The fill-tube is 1" inside diameter vinyl tubing.

This is as simple a design as I've seen for a DIY sub-irrigated grow box. The people at the Rooftop Gardens Project are experts in the science and art of rooftop gardening. They know how to make things from recycled materials in the simplest way possible. I consider them the world leaders in this field.

This grow box is made in the fashion of the commercially available EarthBox, Tomato Success Kit and the Garden Patch Grow Box. There are others along with several D.I.Y. versions on the web.

As Bruce in Chicago has pointed out, the Rubbermaid tote boxes are not made from UV resistant plastic. This will shorten the life of the boxes. You should question the supplier of ready made planters about the UV resistant qualities of their plastic and their estimated useful life before buying.

Comments

[Joseph]

Great idea to use polystyrene for the supports - has it been tested long enough to show that it will withstand the weight and conditions?

Regards
Joseph

[Greenscaper Bob]

Good question Joseph. Consider this a "beta test" planter for me personally, but well tested by the Rooftop Garden Project. This 3/4" thick material is sturdy stuff. As always, I'll report progress.

[Joseph]

I see you get up as early as I do...! I had seen this design at the RGP site but thought the material used was a hard plastic or similar. I'm going to try this with a round bucket I've been eyeing lately to transplant one of my Tomato plants which has outgrown it's pot.

[Greenscaper Bob]

Good out of the box thinking Joseph. This method of creating a reservoir definitely has wider applicability than just these tote boxes.

[E Bone]

I have really enjoyed making some homemade grow boxes, with great results in less than one month. I am already eating lettuce that I planted 24 days ago. I've also made some sub-irrigating planters for houseplants out of two liter bottles. I found all the plans online, posted by generous persons like yourself. Thanks!

One question. Where were you able to purchase polystyrene panels? I have not been able to locate any yet. I want to try that method versus using two totes for each grow box. It seems less wasteful. Also, it seems like a good way to convert traditional pots to sub-irrigated systems.

[Greenscaper Bob]

Nice going on making the planters!

I bought a package of Panel Foam (eps insulation board) at Lowe's. The cost was about $7 for 6 pieces (3/4" x 13 5/8" x 48") I would think that it is available at other DIY stores. Also consider using vinyl floor tiles. The objective is to have the box be easy to make without power tools.

[E Bone]

Thanks for the response--I'll check out Lowe's today. In terms of viral ideas, your idea to make two liter bottle planters is contagious. I am infected, that's for sure. I already gave four bottle planters to different neighbors. These neighbors are also watching my sub-irrigated grow boxes with a lot of interest. Several neighbors have agreed to collect two liter bottles for me, as well.

It seems that the only "problem" with sub-irrigation is that it forces one to confront how inefficient (and how prevalent) drench and drain watering is. I have several potted plants that must be converted to sub-irrigation because I just can't bear to see them struggle with drench and drain watering anymore, a struggle that was made obvious to me only by the thriving plants I have in sub-irrigated systems.

[salvia71]

hello ! i find this design interesting and am planning to make some like it. have you had a chance to try it out yet ?

[Greenscaper]

I grew peppers on my fire escape this past summer. All of the sub-irrigation planters worked very well including the tote box planter even though there is only a half day of sunlight on the fire escape (east facing). To see pictures, search on the word 'peppers' using the Google search box (upper left column).

[salvia71]

thanks for letting me know that. so the design as shown is supportive enough for the weight of the wet soil ?

[salvia71]

also, can you tell me in more detail how you made the grid and how you went about shaping the platform to shape and be flush with the inside of the container ?
on the grid, is this fitting together like a 'tongue and groove' ? i'm trying to determine how the water is able to flow under the grid.
thanks for your attention !

[Jennifer]

Would you please provide more information on how to make planters out of two liter bottles? I just can't visualize how to make them. The ideas here are wonderful, and I can't wait for growing season to begin! Thank you so much from a novice gardener.

[Brigitte]

Here'a link to another great site for reservoir containers: http://www.green-trust.org/freebooks/Earthbox.pdf
I'm trying to design a system for wine barrels. I think they could be more attractive than the plastic bins.

[Jay3fer]

Well, this is the one that actually inspired me to build my own self-watering planter to grow tomatoes in:

Here's my initial blog entry showing building and planting it up:
http://ronypony.blogspot.com/2009/05/wonderful-world-of-sub-irrigation.html
(full credit & link back here given, of course)

Since this entry, I have built a second one with the "leftover" insulation. And there's enough (from $6 worth of pink foam insulation) to build a third if I choose to!)...

[Diane]

I wasn't able to find the polystyrene insulation at Lowe's but this material is commonly used as a packing material. A little dumpster diving can turn up sheets of this stuff - all for free.

As a bonus, I found bags of potting soil with small rips in the bags in the trash of my local Big Lots.

I also buy my 18 gallon containers at Big Lots since they are only 5 bucks.

[Greenscaper]

You're very resourceful Diane. I have a friend who buys ripped bags of potting soil from H.D. at greatly reduced prices. I'm amazed at the stuff he picks up in his truck. The stores throw it out because it costs more than it's worth to ship it back to the distributor or manufacturer.

[camille lawrence]

Has anyone thought: instead of the holes in the corners where soil is packed down...eventually oozing into the water reservoir chamber and over time becoming a muddy sump...how 'bout covering the chamber with a sheet of something like 14 count plastic canvas with a strip of polyester batting (capillary mat) on both sides of the platform for wicking up the water. This would keep 90% of soil OUT of the reservoir so, in long term use for large, permanent plants (ie. fruit trees, etc)it would prevent buildup of soil ooze in the sump. Also...as the Rubbermaids are not UV protected...is it possible to "paint" or "coat" each unit with something to help in this matter for longer-term use??