Introduction: Sub Irrigation Planter Box
I needed to create a quick, and cheap planter to grow some vegetables on my deck. Here's how I chose to do it.
Step 1: Get Your Materials
My challenge for myself was to:
- Make the whole thing as cheaply as I could
- Use only the tools I had at home, which are an electric drill, a 6" mini hacksaw and a hammer
To make things simple, I minimized sawing as much as possible. Since you can find 4' and 3' stock sizes at Menards/Lowes, I decided on making a 4' x 3' x 1' planter.
For the planter box:
- 1" x 8" x 3' Tongue & Groove car siding (Link) [Found these for $1.89 each] -- 6 nos.
- 1" x 8" x 4' Tongue & Groove car siding [Found these for $2.49 each] -- 6 nos.
- 1" x 2" x 6' [Found in the value wood section for $1.69 each] -- 2 nos.
- 1" x 10" x 3' Pine Board (Link) [The most expensive of the lot, $4.09 each] -- 4 nos.
- 2" x 4" x 3' Lumber [$1.39 each] -- 2 nos.
- Some protective wood stain (clear) - [$14]
- 1.5" wood screws, 0.5" nails - [$5]
- Flex-Drain 12' Perforated Drain Pipe from Rural King [$5.99 each] -- 2 nos.
- Landscape fabric 36" x 50' from Rural King [$5.99 each] -- 1 no.
- 2" x 24" CPVC Pipe from Rural King [$1.99 each] -- 1 no.
- 100% PEVA curtain liner [$11.99] -- 1 no.
Total building material cost with tax = $106
For the soil:
- I read on blogs and websites, that for sub-irrigation planters, I should use potting mixes, not soil, since it facilitates the wicking action to bring water to the surface. It's the cheapest I could find. I'm going to trust in it's quality for the time being. If things don't work out this season, I'll invest in more expensive soil next year.
I found a great deal on 'All-Purpose Professional Grower's Mix (2 cu. ft.)' (Link) [$11.97 each] -- 2.5 nos.
- Jobe's Organics Vegetable & Tomato Fertilizer [ $3.99 each] -- 1 nos.
Total soil cost with tax = $36
Step 2: Build the Frame
- Assemble the 3' and 4' tongue & groove boards, 3 per side
- Cut the 2x4s pieces into 11" pieces; we need 4 pieces for supports at the 4 corners of the box
- Attach the 2x4s on each side of the 4' board assemblies from Step 2.1. I drilled pilot holes first, followed by using the wood screws to secure the pieces together. Piece of cake!
Step 3: Work on the Base, Prep the Boards
- At the base of each of the 4' sides, attach the 1x2s using wood screws. These will be the base on which the base boards will sit.
- That's it, as far as making the frame goes.
- Apply an even coat of the protective stain on all the exposed surfaces. Let it dry in the sun for a few days.
- Lay the 1x10x3 pine boards on top of the 1x2s. They were fairly snug and secure, so I did not see the need to use any screws/nails.
Step 4: Attach the Liner
I used a 100% PEVA shower curtain as my liner of choice. Not only did I have one lying around, it was much cheaper than buying a pond liner. Based on my research online, PEVA is used in many food grade bags (ziplocs), as well as for baby bibs and toys. I was satisfied it's safe enough to use for my planter. Do your research though! YMMV!
I attached the liner to the inside of the planter using 0.5" nails. Getting it flat and folding the edges is tricky. Take your time.
Step 5: Prepare the Perforated Drain Pipes
- Expand the perforated pipes.
- Cut them to size (4' length each) so they'll sit snug in the frame lengthwise. I chose to have a total of 4 pipes.
- For one of the pipes, cut a 2" hole on one side to make space for the 2" CPVC fill tube.
- Cut the fill tube to length. Originally 24", I only need it to be 12". Cut it at a 45 degree angle preferably.
- Cut the landscape fabric as needed to snugly wrap each tube. Keep ~4" of fabric on either side of the tube that you can crumple it up and stuff the tube ends. This'll keep the soil from entering the tubes later.
- Remember to cut a hole in the fabric as well for the fill tube.
- Insert the 45 degree angle side into the hole you've just cut. The angled cut will allow water to flow easily into the perforated tube.
Step 6: Add a Drain Pipe
- Drill a hole on one side at a level in line with the top of the perforate drain pipes.
- Prepare a small drain tube. I used the suction tube from an old liquid soap dispenser. I attached landscape fabric on one side, to avoid soil getting into the drain pipe and clogging it up.
Step 7: Add the Pro-mix to the Bottom Layer
Fill the entire bottom of the planter with the potting mix. Make sure to fill all the nooks and crannies around the pipes. Make sure to distance the perforated pipes evenly while doing so.
Tip: cover the fill tube with some plastic so you won't get any soil in the tubes.
Once complete, cover the soil with a sheet of the landscape fabric. This'll help keep the lower layer undisturbed, while still allowing the water through.
Step 8: Prepare the Top Layer
- Fill the rest of the planter with the soilless potting mix
- Mix in the fertilizer per the instructions on the bag
Step 9: Fill With Water, Plant Away!!
Fill the planter with water. The first time you fill the planter, it'll take time to completely fill each perforated tube.
It's now ready to plant!
Update - Jun 2 2015:
The plantlings are growing strong...
Update - May 23 2015:
Progress of the SIP here! Plants are doing well!
Update - May 13 2015:
Hey everybody, based on some of the questions in the comments below, putting together a sort of FAQ here:
- Why are the pipes not connected? Would the pipes other than the one with the fill tube be empty?
- The pipes can be connected. Instead of 4 separate pipes, use 2 U-shaped or one 4-edged serpentine pipe. It won't matter, as long as you have them separated by a packed layer of the potting mix. This vertical packed layer is the wicking medium which pulls water to the top.
- Potting mix allows water to flow through real well. There is no concern for the other pipes remaining empty / half filled.
- Just to confirm this (especially after all the questions!), I excavated to the bottom of my planter. I dug up 1/3rd of the top layer away. I confirmed that there was water everywhere! Looked perfect.
- I experimented around too. I started filling the planter through the fill tube and observed how the 1st tube filled, and how quickly the water started moving to the remaining tubes. There was very little delay in filling the water from one tube to the other. Water reached across to the overflow tube pretty quick and drained out just fine.
- So, fear not! Use the design and make modifications boldly!
- How often must I re-fill the planter with water?
- I don't know exactly for this size planter and design. I've read it could be as sparse as once a month to once in 2 months. I'll keep this page posted.
- Is the endeavor worth it from a return on investment standpoint?
- This is a good question if you plant vegetables to save money at the grocery store. Last year, my wife and I did save a lot of money when we planted straight into the ground.
- For me, this project was about having some fun building something and having a nice planter to look at on my deck. So, how do I put a price on that?
- If you want an ROI, remember to amortize the cost of the project over the life of the planter, in addition to it's yearly maintenance costs.
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