Learn exactly how to build a DIY self-watering planter box. This sub-irrigation modern raised planter is perfect for any yard!
My biggest challenge with keep plants alive is remembering to water them. I have tried hard and although I have successfully kept low-maintenance houseplants alive, I struggle to keep the vegetable garden alive.
This spring I decided, I wanted to built another vegetable bed but this time, it needed to make things easier for me.
So I researched and built a raised self-watering planter!
This is a perfectly self-sufficient self-watering system (also known as a sub-irrigation system)- no need to run drip lines and find a water source. You just need to fill it up every few months!
Table of Contents
Material needed –
- Lumber per the plans
- 2½” pocket hole screws
- 2½” exterior grade screws
- 5/16″ staples
- Exterior grade wood glue
- Duct tape
- Stain in the colors of your choice. I like to use exterior-grade deck stain
For sub-irrigation system
What type of wood to use
For exterior planters, redwood and cedar are the best choice because they last a very long time. However they tend to be expensive.
Pressure-treated wood is the next best alternative and is totally safe because there is a liner between the soil and the wood. However, you have to be extremely careful and wear all the safety gear when working with pressure treated wood because of all the chemicals it contains.
I used Douglas Fir, which I have used in the past on projects have withstood the elements for over 3 years. They will probably not last as long as a cedar or redwood planter, but I am happy with it.
How to build the self watering planter –
Below is the complete video showing exactly how I built the planter. The full step-by-step instructions follow below.
Step 1 – Make the cuts and pocket holes
- Make all the cuts per the plans.
- Make the pocket holes in the 2×4 boards for the bottom stand.
Step 2 – Build the box
- Attach the 2×2 to the 2×6 boards to form the sides using 2½” exterior grade screws.
- Attach them together to build the box.
Note – at this point the planter will start to get very heavy and it is advised to move it and build it at it’s final location.
Step 3 – Build the base
- Build the base using 4×4 and 2×4 boards with 2½” pocket hole screws and wood glue.
- If you intend to stain it in a dual-tone like me, this is a good time to stain the base.
Step 4 – Attach the planter base
- Place the stand on the top of the planter and attach using 2½” exterior grade screws.
- Lay the 2×4 planter base and attach using 2½” exterior grade screws.
- Stain and seal the top planter box.
The planter is ready. At this point, it will serve as a regular planter. If you intend to do so, you can simply drill drainage holes in the bottom, add landscape fabric and start planting.
But we are building a self-watering planter so let’s go ahead and do that!
How to set up the self-watering system –
Step 1 – Add the pond liner
Attach the fish-safe pond liner to the insides of the planter using a staple gun. It is very important to not cut the liner at all – even on the corners. On the corners – simply fold it in to create corners.
Step 2- Add the drain pipe
- Stretch out and cut the perforated drain pipe to a size equal to the length of the planter. This is important. It should sit as tight as possible inside the planter.
- Cut enough pieces to completely cover the bottom of the planter with only a little spacing between the pipes.
- Cover both ends of the pipes with landscape fabric and duct tape.
- Lay the pipes in the planter.
Step 3 – Add the inlet pipe
- Cut the bottom of a PVC pipe at a slight angle. I cut it at 22.5-degrees.
- Using a utility knife, cut a small slit in the perforated drain pipe just large enough to fit the PVC pipe. This should be rather tight. If it isn’t, you can use duct tape to cover the opening.
Step 4 – Add the overflow drain
- On the diagonally opposite corner of the planter, on the bottom, drill a hole large enough to fit the ¾″ hose.
- Make a small slit in the pond liner and the perforated drain pipe and pass the hose into it.
- Seal around the slit of the pond liner with duct tape (I did not do this and ended up with a leak because of it)
Step 5 – Add the potting mix
- The first layer is a mixture of vermculite and peat moss in a 2:1 ratio. This mixture should go in between the drain pipes and cover them completely.
- Over that, you can add regular potting mix and plant your favorite plants!
That’s it! The self-watering planter is ready for action.
The self-watering planter in action
Using a garden hose, fill in the water through the PVC drain pipe.
It took about 6-7 minutes for the water to completely fill up and start flowing out of the drain hose in the back. This is it! The perforated drain pipes are now full of water.
Even though they are not connected, the vermiculite and peat moss allow water to transfer between the pipes and fills them up. Now the soil will keep wicking the water as needed.
Many tutorials call for a fabric covered perforated drain pipe. That can be used as well. I wasn’t able to find one in stores close to me. I found many tutorials referring to a simple perforated pipe as well, so I decided to use that.
How does this work?
“Shouldn’t the pieces of pipe be connected?” This is the most common question I get. Nope, they shouldn’t be. If they were, water would just go in one end and flow out on the other without being held.
The way this self-irrigation works is that water fills in one piece and overflows out of the holes. It gets absorbed in the vermiculite. Vermiculite is like a sponge and can only hold a certain amount of water. Once it is saturated, the rest of the water flows wherever it can find space – the holes in the adjoining pipe. This process continues until it reaches the last piece and overflows.
This is why it is important to completely cover the bed with the perforated pipe. It will make it more efficient for the water to flow AND will hold more water which means longer times before needing to refill.
DIY Self-watering planter printable plans
You can get the full printable plans for this modern DIY planter including all the instructions for the sub-irrigation system below.
After about 4 days of filling and in 80-degree days, the inside of the soil is still damp which means that the system is working.
Stay tuned to see how this works in the future and how long before re-filling the water. I am hoping it is going to be a few months, but we will see!
We started a whole bunch of seeds, and the kids are excited to plant them and watch them grow this season!
7-week Planter Update
It has been 7 weeks since I set up and planted the first tomato plant. 2 weeks later, we also planted a cucumber and chili plant. They are thriving! Look close to see all those tomatoes!
We haven’t had to re-fill the reservoir yet. We live in Southern CA and have definitely had a few 80F+ days. But the soil under the top layer is still damp, so we are good to go.
I will be keep updating this post as time goes by so stay tuned!