Watering plants can be a little bit of a hassle. Overwater and you risk root rot. Forget to water and you may find a wilted dying plant gasping for life. This is especially problematic when leaving town for a few days. What’s a homeowner to do?
A lot of people are promoting these DIY plastic bottle drip irrigation projects as a solution. I did some research on this with Google’s help and here is basically what I was promised:
You can build a plastic bottle self-watering system with just a few tools that you probably have on hand. There are different approaches to building these and their effectiveness varies but it can be a fun DIY irrigation project for plants.
I have seen many thrifty DIY enthusiasts promoting the use of plastic bottles to create slow-release watering systems for garden plants and flowers. While the idea of plastic bottles sticking up throughout my flowerbed isn’t exactly appealing, I will admit to being intrigued by the concept.
I recently implemented a simplistic DIY automatic irrigation system for my flowerbed but there are possibilities for this type of project as well. If effective, it could serve as a viable solution to watering indoor or porch plants while away for a few days. Plus, I could put those plastic bottles to some use instead of sending them to a landfill.
Drip Irrigation Using Plastic Bottles
I searched the internet and studied different techniques for using plastic bottles to create drip irrigation. There are essentially three approaches to this.
The 3 primary techniques of using Plastic Bottles as drip irrigation devices:
- Hanging above the plant (this is the truest form of “drip” irrigation)
- Sticking up with the cap-end Buried in the soil (In-Ground, Upside Down)
- Buried with only the top of the bottle sticking out of the soil (Bottle Buried To The Cap)
I want to spend a little time looking at the concept and potential issues of each of these before we get into the testing.
Hanging Drip Irrigation
This is the most complicated approach but it does stand the highest potential of working as a longer-term solution. The reason this has a high probability for success is that it eliminates the problem of holes getting clogged up by dirt that is inherent with both of the other techniques.
The problem with this approach though is that its not exactly stealthy. You have to have big soda bottles hanging upside down over your plants. So, yeah.
In-Ground Upside Down Irrigation
I found this technique on the You Grow Girl website. The concept behind this is incredibly simple. You drill a few tiny holes in the cap of a plastic bottle and cut out the bottom. You then fill the bottle with water and stick the cap-end directly into the soil.
I had my doubts about this in-ground method. In theory, gravity and resistance will work against each other to allow for a slow but steady release of water into the soil. In theory, at least. But what about soil clogging up the holes? Would that be an issue?
Buried Bottle Irrigation Technique
This method was found on Bob Villa’s website so I anticipated really good results. It relies less on gravity and resistance (though those do play a role) and more on the idea of the soil and root system pulling water in as it needs it.
In this technique, you poke holes all over the sides and bottom of a plastic bottle and bury so that only the cap is sticking out. You then cram a sock into the bottle.
The sock, as explained on the Villa website, is meant to absorb water and slowly leech it out to the rooting system as needed. You then fill the bottle with water and, if it works, the water will slowly and steadily seep out as the moisture level of the soil demands.
This approach makes sense from a conceptual standpoint because plant soil will essentially act like a sponge (source) and pull in the water that it needs until it reaches its ideal saturation point. But I saw the potential for oversaturating as well.
This method does not rely as heavily on gravity as the other two do.
Talk Is Cheap – Let’s Test These Techniques!
In each of these techniques, you potentially have a cheap and easy way to water plants while you are away. But do they actually work well enough to justify them as a viable DIY solution?
I decided to put this concept to the test and see if it was really the ingenious idea that it’s praised to be.
The test tubes for this experiment were one 2 liter bottle and 2 20 ounce bottles.
Hanging Plastic Bottle Drip Irrigation Technique
For this test, I cut the bottom out of a 2-liter bottle using a box cutter. Be careful with this step! Safety first.
Next, I cut small holes on each side of the bottom and wrapped string through them to create a hanger. It’s not perfect but for a cheap DIY project like this, it should work just fine.
Finally, I hung the bottle over my test potting plant and filled it with water. Make sure the cap is on snug when you do this.
Once the bottle was full, I slowly loosened the cap to allow water to seep out. This takes a little adjusting. Depending on how much water you want to allow the plastic bottle to drip, you will need to be very accurate in “dialing in” the drip-rate.
With this project setup and ready for testing, I moved on to the next technique.
Upside-Down In-Ground Plastic Bottle Irrigation Technique
Using a 20-ounce plastic water bottle, I removed the bottom as I had done with the 2-liter. I then began drilling a series of holes in the cap with a small drill bit.
The key is to put enough small holes to allow for a slow and consistent water flow that can be equalized but not eliminated by the resistance of the soil. There was a ridiculous amount of trial and effort with this.
Buried Plastic Bottle Irrigation Technique
This project involved drilling small holes in the sides and bottom of our 20-ounce bottle. This proved very frustrating. Whenever I tried to drill into the side, the bottle would crush from the pressure.
I finally managed to get the holes drilled and then stuffed the sock into the bottle (not an easy task to get it through the hole – guess that’s why it’s called a bottleneck).
I actually ended up cutting the sock in half and pushing it in through the cap hole a piece at a time.
Of all three techniques, this one was the most difficult and frustrating to set up.
Testing The DIY Drip Irrigation Projects
I wanted to make sure that I had a controlled and consistent testing environment for each of the techniques. This was necessary to ensure that the circumstances between each test did not influence the results.
I purchased three pot plants for the test from Walmart. They did not have seep holes in the bottom so I drilled one hole in the center bottom of each. I then filled each to the same level with Miracle-Gro Raised Bed Soil. This gave me three testing pots using the same material in the same quantity.
I set up the three testing pots with their plastic bottle drip irrigation systems under the porch so that rain would not affect the results.
To begin the testing, I filled each with 10 ounces of water. Although I anticipated each would dissipate water at a different rate, my goal was to ensure that I used the same amount of water during a 24 hour period for each test.
I quickly realized, however, that there was no need to only fill the 2-liter bottle with 10 ounces. I began filling it with 1 liter of water at once. I would then continue to add water to the other two projects as needed up to 1 liter.
For 27 days, I monitored the water levels in the bottles and the saturation level of the soil in each of the three containers.
The DIY Plastic Bottle Drip Irrigation Findings
My testing ran for a total of 27 days. During that time, I had to make modifications to one of the methods (explained later in this article). Overall, the results of this test were interesting, if not entirely anticipated.
I don’t want to bury the lead, so below are the test findings. I’ll get into the details behind each of these below.
|Technique||Days Of Successful Operation||Probability/Viability||Disadvantage|
|Hanging Bottle||27 days||High||Ugly|
|Upside-down cap in-ground||13 days||Medium||Potential For Clogging|
|Buried Bottle||less than 24 hours||Low||Unreliable|
- The hanging bottle technique proved to be the most reliable method of DIY drip irrigation, providing a consistent drip rate throughout the entire test.
- Coming in second was the upside-down in-ground method. It worked but was prone to clogging (see my modifications below on how to solve this).
- The biggest fail in my testing was the buried bottle technique. This proved completely ineffective and not worth the time and effort.
I have to admit that I was surprised and thoroughly impressed with the hanging bottle drip technique. Once I adjusted the cap to the desired drip rate, this project worked flawlessly throughout the entire testing. Here is a short video showing the consistent drip from the bottle:
I did fine-tune the drip rate once or twice. I believe that the cap loosens or just allows more water to drip through as time goes on, but it was minimal. I was aiming for precision. I could have easily left it alone and it would have been just fine.
Yes, the hanging bottle approach worked best. But it looks a little goofy hanging over your plant. Somehow it becomes the accent in your yard instead of the plant itself.
In fact, when I was rigging this apparatus up my wife commented on how well it would go with a toilet planter in our front yard. 🙂
So, yeah. There’s that.
Upside-Down In-Ground Test
So what was it about our Upside-Down In-Ground test that caused it to come in second? Why couldn’t it reign as champion in this test?
Remember in the beginning we established that gravity and resistance would provide the push-pull to make this work. When effective, gravity will force the water toward the holes. The size of the holes and the soil with provide resistance so as not to allow the water to flow out too quickly.
And herein lies the challenge. Too little resistance and the water will flow too quickly but if the holes are too small they will get clogged up. So it’s not just a mindless exercise. There’s a little test-and-verify involved.
I wanted to see if there was a way to make our stealthier upside-down technique more effective. And so, in the spirit of overkill, I tried a few approaches to solve this.
Why The First Test Failed
The first test had involved simply sticking the bottle into the soil as is commonly promoted. This turned out to be a dismal failure with the holes clogging within the first 24 hours. At first, I thought that I’d miscalculated my drip rate and needed to add more holes but when I pulled the bottle out of the soil it was clear that the holes had clogged.
I decided that this may have been a fluke so I cleaned the holes and replaced the bottle. As it turned out, the upside-down in-ground plastic bottle drip irrigation technique actually worked. It kept the soil moist for almost three days before clogging again.
Of course, if you are dealing with having to unclog these things every couple of days, its probably not worth the effort. Still, I have to admit that I was not able to disprove the conceptual effectiveness of this DIY project.
By its very design, it is prone to failure from eventual clogging so I would not rely on it as a long-term solution. On the other hand, if you are just needing a way to keep your plants moist for a few days while you are away, this approach actually has merit.
How To Improve The Upside-Down In-Ground Plastic Bottle Drip Irrigation Design
If you were needing more of a longterm solution, an improvement could be made to the design by adding a screen of some sorts between the holes and the soil.
But there’s a catch. You would not want to press the window screen material directly against the bottlecap as this would still allow for clogging. The key to making this work is to put space between the holes and the soil.
For this, we need some form of aggregate.
I first used a cotton ball to serve as an aeration buffer between the soil and the holes in the bottle cap and it worked surprisingly well. The cotton absorbs water through the holes but has enough surface space to prevent clogging, at least in the 13-day test that I conducted.
The point is the cotton keeps the soil from clogging in the holes. As long as the holes remain open, water will pass through.
My only concern with the cotton ball as the screening buffer is that it will eventually become saturated and will not take on additional water. This could prevent the system from leaching water into the soil.
So this is what I came up with. It’s crude but a simple and potentially sustainable solution.
I cut a small piece of window screen that I could wrap over the top of the bottle cap. Next, I used some bagged Perlite and filled the space between the cap and the window screen to create space between the holes and the soil. Finally, I wrapped a rubber band around the screen at the base of the bottle. This held it firmly into place.
The result? I ran the final test for 13 days and it worked flawlessly. I still think it would clog up eventually but with the Perlite and the window screen ensuring a space between the dirt and the bottlecap holes, it’s nowhere near as likely as sticking the bottle cap straight into the soil.
Summary Of Findings
In the end, the hanging bottle technique proved to be the simplest and most reliable method for creating a DIY plastic bottle drip irrigation system. Once the cap’s flow rate was adjusted, the bottle provided a consistent and reliable drip-rate throughout my testing. Because of the large and clunky nature of this technique, it would be best suited for outdoor use.
With needed modifications, I was able to establish a trustworthy watering process using the upside-down plastic bottle drip irrigation method. This technique would be best suited for an indoor plant that requires water for a few days while you are away.
I found no viable use for the buried-to-the-cap bottle approach. I’d had higher hopes for this method since it is the least obtrusive of the three. Unfortunately, the lack of leveraging gravity like the other two methods causes this one to fall short of expectations. You still have the resistance of the soil but without the force of gravity, the water was not able to leech effectively.
Are Plastic Bottle Drip Irrigation Solutions Worth It?
If you are looking for a really cheap and easy DIY solution for occasional watering needs, sure. Either of the two successful methods can be used. Would I recommend either of these as longterm irrigation solutions? No.
First, while they do provide some level of reliability, it is nowhere near the accuracy that you will have with an electric timer or other modern irrigation systems. You could get by with these methods for a few days here and there but when it comes to duration, these are not really meant to be longterm solutions.
Second, these are not attractive solutions. They may look fine in a backyard garden where aesthetics is not your top priority but they are not going to complement a flowerbed or decorative plant feature in your front yard.
Despite my skepticism, I have to concede on these plastic bottle drip irrigation solutions, in concept at least. There’s a little work involved in getting a proper flow and the upside-down buried cap method it is prone to clogging if you don’t add a buffer between the holes and soil but, yes, a gravity-based irrigation system like this does work.
For plants on your porch or in your house, this may be a good way to keep them watered when you are away. I wouldn’t recommend it for a permanent solution though. Consider instead these indoor plant watering stakes (link to Amazon). And an alternative outdoor irrigation solution for plants such as the automated watering system that I use for my flowerbed.
The key to this type of project is understanding its limitations and its place. If you like DIY projects and are looking for a quick and easy way to passively water your plants in a pinch, it may be exactly what you are looking for.
Just remember that these are meant to be cheap and easy DIY projects. They are utilitarian band-aide solutions, not aesthetic ones designed for longevity. In the end, you get what you paid for. They work but they aren’t pretty and may not hold up to long term use.