How to create a self-watering system for window boxes

Our century home came with built-in window boxes on the second floor. As I am not much of a gardener (I have a habit of forgetting to water my plants), I found the idea of putting plants into the window boxes quite daunting. In fact, last summer (our first summer in our new house), I didn’t plant anything in the window boxes at all because I was intimidated. As a result, I felt like our home didn’t look well-cared for. Empty window boxes (which are on four of the five windows on the front of our home) look very sad. So this year, I was determined to at least try to plant some annuals in the boxes. In order to decrease the likelihood that I would kill them, Brian suggested creating a self-watering system for each of the window boxes.

It turns out that window boxes are a lot of work; especially when they are on the second story so you have to do all the work by reaching out the window from inside the house. I can tell you that we got dirt everywhere. And spend hundreds of dollars on plants. But, I have to admit they look much better with plants in them.

The previous owner (with whom we are still friends) indicated that she would have to water the window boxes daily (or twice daily in the case of the window box on the back of the house because it gets a lot of sun). Brian did some research and essentially determined that if we put in a bit of work up front to create the self-watering system, we could save a lot of time watering in the long run. We considered purchasing pre-made systems but found that they were quite expensive and could not be customized to the specific sizes that we needed.

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The building process

So Brian designed a custom self-watering system that would significantly reduce the frequency of watering (which is a huge pain because the windows are 100 years old and are not easy to manipulate). This project ended up being quite easy to construct, however it was a bit of a pain to install under the existing soil in the boxes. 

In order to complete the project we purchased PVC pipe, connectors, cotton rope, and PVC cement. Based on the size of our window boxes (which are quite deep but somewhat narrow), we chose to use 2” PVC pipe for the bottom of the box connected to a 1” piece protruding from the soil. We cut the pieces of 2″-wide PVC to size using a miter saw. Next, we used a drill to make holes about 4” apart into the top of those pieces of PVC. We then cut the rope pieces to about 12” and knotted them in the middle to prevent them from slipping too far into the pipe. A rope piece was added to each of the drilled holes.

We then added the PVC elbow to one end and a cap to the other. On the elbow end, we added the adapter and bushing along with a short piece of 1″-wide PVC. This piece of PVC will protrude from the top of the soil line and be the spout through which we add water to the system.

Essentially, the way this system works is that the rope pieces act as a wick and absorb water from the pipes. In this way, they slowly distribute the water throughout the window box from the reservoir below. As a result, the water lasts much longer because it doesn’t evaporate as it would if you watered the plants from above.

Once all of the pieces were cemented together, we placed them in the bottom of each of the window boxes. We were sure to place the ropes so that they were spaced evenly and spread across the bottom of the soil. After covering the system with soil, we added the plants. Other than the small piece of PVC sticking out of the soil, the system is completely hidden.

There was one change we would make to this project if we were ever to do something similar in the future. We would add some sort of glue or adhesive around the rope holes that would provide a seal. Without that seal, we can’t tell when the system is full of water because the excess water just seeps out of the top of the pipe through the drilled holes. This would make it much easier to determine when the system was completely filled.

Tools and products used

Below is the list of tools and products we used for this project (for each window):

1. 2” PVC pipe (should be about 4-6” shorter than your window box)
2. 1” PVC pipe (should be cut to the about 1” longer than the depth of your window box minus the height of the elbow)
3. 2” PVC elbow
4. 2” PVC cap
5. 1” x 1” dia adapter PVC fitting
6. 2” x 1” dia bushing PVC fitting
7. PVC cement
8. Braided cotton rope
9. Miter saw (to cut pipes to size; this could also be done with a hand saw)
10. Drill (to drill holes for ropes)
11. Scissors (to cut rope to size)

Project conclusion

It has been over a month since we installed the self-watering systems and so far they seem to be very effective. I generally only water the boxes at the front of the house every five or six days. The planter at the back of the house has to be refilled about every three days because it gets so much sun, but this is far preferable to the multiple times per day that the previous homeowner reported. 

This project could easily be adapted to work in a raised bed or other container as needed. You would just need to adapt the pieces of PVC pipe to the shape and size of your container.

If you are looking for more home improvement inspiration, check out my post on how we built inexpensive basement storage shelving using 2x4s. You might also like my post on how we made a concrete table top.

I am very excited about this project and hope that it will help me to keep the plants alive (because I think that window boxes with dead plants are even worse than window boxes with no plants).

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