How to make a genuinely ‘self-watering’ container garden

by Mark Ridsdill Smith on

in Blog, DIY projects, Featured home page

These wooden containers have reservoirs underneath that are constantly topped up by from the water butt on the right.

These wooden containers have reservoirs underneath that are constantly topped up by from the water butt on the right. The water butt is made out of an old olive barrel!

DIY Project: Level 3 (Harder)

If you’re looking for a highly productive and elegant growing system that is genuinely ‘self watering’, this system from Canada is brilliant!  I’ve graded it ‘Harder’ because you need a few specialist tools and some practical DIY skills. But anyone who’s happy to tackle simple carpentry or plumbing jobs at home – and has a bit of patience – should have a crack at this. The investment of time and effort will repay itself in time saved watering and higher yields (5kgs of runner beans came off just one of these containers in a summer  – more on how reservoirs increase yields here.) 

If watering is a big issue for you and you don’t feel up to attempting building this – don’t worry! There are other systems that are much easier to construct that I’ll be testing and writing about in 2013.

The idea behind this system was adapted from the free, downloadable guide: “Guide to setting up your own edible rooftop garden“, by Rooftop Garden Project, Montreal, Canada – who I’m indebted to for many fantastic ideas! If you decide to build your own, please use this guide in conjunction with my notes below.  There is lots of scope to adapt the idea in other ways, too – I’d love to hear from you if you decide to experiment.

You will need:

A horizontal surface that the containers will finally sit on (each container must be at the same level or the the automatic self watering system will not work), plus:

– Wood to make the boxes (I used soft wood found in a skip; hard wood would be better if you can lay your hands on some).
– Corrugated plastic sheets to make the false bottoms (I used old estate agent signs).
– 110mm (4inch) drainage pipe. 80mm can also be used but 110 mm is better if you can find it (lengths are commonly discarded in skips).
– Large empty plastic boxes, one for each container, to act as reservoirs (I used old 50 litre recylcling boxes) and one plastic container to use as a ‘control box’.
– Zip ties, ring ties or cable ties (different names for the same thing).
– Screws.
– A drill, a 110mm hole saw, a mitre saw, and screwdriver.

Here’s how to do it 

1. Construct the wooden boxes. One advantage of using wood is that you can create boxes to fit the size of the space.  You can preserve wood with Osmo wood oil or linseed oil, and line the wooden boxes with plastic to slow down the rotting. Be aware that the weight of a large wooden box plus soil can be considerable (I placed these boxes on top of a load bearing wall to hold their weight).

This shows the simple wooden boxes with the plastic reservoirs in the bottom. The right hand box also has it's 'feet' cut, ready to attach to the corrugated plastic.

This shows the simple wooden boxes with the plastic reservoirs in the bottom. The right hand box also has it’s ‘feet’ cut – grey 110mm drainage pipe. The corrugated plastic false bottom will rest on top of these feet.

2. Find a plastic container that fits inside the box to act as a reservoir (the green boxes above). This reservoir needs to be 15cm – 20cm (6 – 8 inches) high – you can use a hacksaw or jigsaw to cut the top off if it’s too tall (I used old 50 litre recycling boxes, and cut the top off). The reservoir does not have to be the exact size of the wooden box – just large enough to hold a reasonable supply of water. If the plastic box has holes in the bottom (most recycling boxes do, unfortunately), you’ll need to make it waterproof. The easiest way I found is to block them up with a silicone sealant.

3. Drill a 1cm diameter hole about 12 cm above the bottom of each plastic reservoir. This is an overflow hole and prevents overwatering of your plants.

4. Drill lots of holes in the 110mm (4 inch) drainage pipe and then cut it into 15cm (6 inch) lengths (you want 20 – 30 holes in each 6 inch length). You can see the cut bits of pipe in the top right hand box in the picture above. These bits of pipe will next be attached to the false bottom of the container, like feet (you can see them attached, below). Filled with soil they’ll sit in the water of the reservoir and wick the water up into the main part of the container.  The number of ‘feet’ you need in each container depends on its surface area. Garden Rooftops say that the surface area of the feet should be 5 – 15% of the surface area of the container. More than than this and your soil may get water logged, less and it may dry out. For these 60cm x 60cm containers, I calculated that four 110cm diameter feet would be about right.

The corrugated plastic is cut to fit into the box and sits on top of the reservoir. I added a wooden ledge to hold it secure at the sides. You can also see the ‘feet’ attached with ring ties. The surface area of these feet should make up 5 – 15% of the total surface area.

5. Cut some corrugated plastic card (I used old estate agent signs) to fit snugly inside the box. This will sit on top of the reservoir and separate the soil from the water. Drill lots of small holes in the plastic to allow air to circulate into the soil and your plant roots.

6. Using a hole saw attached to a drill, drill 110mm holes in the corrugated plastic, one hole for each foot you’re adding. Keep the round ‘waste’ cut-outs and attach one to the bottom of each ‘foot’ to make a base so that the soil can’t fall out (you can see this in the picture above).

7. Attach the 110mm pipe to the underneath of the corrugated plastic with three or four ring ties. Put this into the wooden box with the feet sitting in the plastic reservoir. Apart from a tube of plumbing to add water, your container is now finished.

8. You can now either simply add a PVC fill- tube (50 – 80mm) by drilling another hole in the plastic false floor and inserting the tube – it needs to be long enough to protrude from the soil when the container is filled.

9. Or you can plumb several reservoirs together and link them up to a control tank (with a ball cock to control the water level). For the plumbing bits you can either use quick-fit (or similar) plumbing sold in plumbing stores or contact a company that sells garden watering systems (like Garden Magic) or hydroponics. See my images below and page 52 of the ‘Guide to Setting up your Own Edible Garden’ for instructions on how to make this. 

Here you can see how the reservoirs are linked together with plumbing pipe and connectors.

Here you can see how the reservoirs are linked together with plumbing pipe and connectors.


Here's the control box - this controls the water flow into the reservoirs. It works just on exactly the same principle as a cistern of a loo. When the water in the reservoir falls, the ball cock opens and lets in water from the water butt. Simple and effective!

The blue box is the control box – this controls the water flow into the reservoirs. It works on exactly the same principle as a cistern of a loo. When the water in the reservoirs falls, the ball cock opens and lets in water from the water butt. Simple and effective!


And here it is in action. It was possible to leave this for weeks - all watered automatically. Unfortunately, not all the containers on the balcony were rigged up to this system so we still needed to get friends round when we went away!

And here it is in action. It was possible to leave this for weeks – all watered automatically. Unfortunately, not all the containers on the balcony were rigged up to this system so we still needed to get friends round to water when we went away!


{ 33 comments… read them below or add one }

Chris G November 5, 2013 at 1:13 pm

Hi Mark ,
Thanks for some great ideas and this excellent DIY guide I’m going to do something very similar with some slight modifications. I do have a question for you though, how long does the reservoir last for you before you need to refill it approximately?

Thanks again,


Mark Ridsdill Smith November 5, 2013 at 1:53 pm

Hi Chris, thanks for your question. Are you referring to the reservoir in the bottom of each container or the water butt that fills up the control tank?



Chris G November 5, 2013 at 2:40 pm

Thanks for the fast reply, I was refering to the water butt that fills up the control tank.


Mark Ridsdill Smith November 5, 2013 at 6:26 pm

Hi Chris, thanks for the clarification. The water butt in the system I used was connected to the downpipe carrying the water running off the roof. As a result it filled up automatically each time it rained – so it was hard to keep track of how often it would have needed to be filled if I’d been doing it manually.

As a rough approximation though, a 120 litre water butt attached to say six boxes should hold enough water for at least two or three weeks during cooler periods when plants are not growing too much. However, on warm days in summer, if you have your six pots filled with thirsty crops like tomatoes and courgettes, each plant could drink 4 litres of water a day (sometimes more) – which means a full 120 litre water butt may only contain enough water for a few days (four or five maybe?) under such conditions.

I hope that helps answer your question?


Chris G November 6, 2013 at 6:52 am

Thanks Mark ,
That helps alot thanks for sharing your knowledge.

Ash September 23, 2013 at 7:18 am

Hi Mark – great article! Just to ask – how many containers would I be able to fit on the one system? It will be a large water butt that it is attached to and I live in Newcastle, so there should be plenty of rain! Thanks


Mark Ridsdill Smith September 23, 2013 at 7:29 am

Hi Ash, I had just three large containers linked to it but I think you can do ten or more (check out the roofguide pdf I link to above for more info). Of course, the more links you have, the more chance you have for a block or leak somewhere.

Whereabouts in Newcastle are you? I’m in South Gosforth now.

Good luck with the system.


Ash September 23, 2013 at 10:09 am

Thanks for the swift reply! I’m in Heaton with a south west facing back yard (concrete, of course) and a north east front. Next door grew some fantastic courgettes this summer in the front so it showa you what can be done! Couldn’t keep up with watering all the containers this year and with all the sun, a lot of my plants perished. However, the tomatoes that survived have done very well with all the sun this year! I have plans to build roughly 8 meters of planters in the back yard out of pallets I’ve been collecting over the winter and a self watering system seems to be a must to supplement watering manually! Your website has been excellent in showing me what is possible in such small spaces!


Mads Boserup Lauritsen August 31, 2013 at 12:29 pm

Hi Mark.

Thx. for an amazing blog, if you ever are in Copenhagen please come visit our small “Roof Tomato” garden.

Next year I’ll try to adapt your principles on our roofgarden, on the Selv watering containers we use.
We are growing alot of different vegetables and flowers, and the project has evolved more or less like your own.

My blog is in danish, but pictures are pictures..

Once again, thx for sharing, and hopefully we will meet one day.

Best regards
/Mads, Copenhagen – Denmark

ps. TagTomat is “Roof Tomato” in Danish…


Mark Ridsdill Smith September 18, 2013 at 7:31 am

Hi Mads
Great images on your website, thanks for sharing. I’d certainly love to visit Copenhagen one day and will be sure to get in touch if I do.


Jens August 21, 2013 at 12:21 pm

Hi Mark! I just finished building the first grow box. It’s 60x60x60cm. I decided to put one extra pipe in there (5 total) because my reservoir is only 8cm high. In all it took me 7 hours working non stop. Had to silicone a bunch of stuff and making the feet took its time! Didn’t add soil yet, just want to make sure everything works first. If I could upload pictures I would :) I understand the outlet of the water container has to be the same level as the reservoir or just a tad higher. I will elevate the reservoirs so I can use a bigger water container. I’m planning to build a few more growing boxes and linking them all up to the system and eventually I will make it automatic by using the toilet refilled system. Time to grow some chili and tomatoes and maybe something really special in the middle if I’m lucky 😉 thanks again for your help mate.


Jens August 21, 2013 at 5:17 am

Started construction now – box and corrugated plastic is all done. Ran into a problem regarding the reservoirs, I could only find 9cm tall ones – drilled the overflow holes at 8cm from the bottom. Yours are at 12cm so worried my box will be too dry. I’m thinking I need to put maybe 5 pipes instead of your 4 to make up for those missing 4 cm. What do you reckon?


Mark Ridsdill Smith August 21, 2013 at 9:43 am

I haven’t tried an 8cm deep reservoir, but I don’t think it will make too much difference. The amount of water that is wicked up into the main container is primarily determined by the surface area of the wicking feet and the capillary action in the soil (some soils will wick water better than others). Have you looked at the Canadian paper I link to on the site? That has some very helpful info, particularly optimum depths of reservoirs and a formula for calculating how many pipes you need.


Jens August 20, 2013 at 1:46 pm

Hi Mark and thanks for the quick replies! I’ve been out shopping for most of the material today. I reckon it will cost me about 50 bucks to build each growing box (120cm x 60cm). The cool thing in Thailand you can get some really tough & hard jungle wood cheap :).

I’ve been thinking about the tank that is feeding the reservoir . You mentioned it needs to be leveled, but for sure the bigger the tank is the higher the pleasure inside thus it will force the water level up inside the 11cm pipes, right? Can you please give a hint of about how high the water stands inside the pipes when the valve from the feeding tank is open? Then I can elevate my tank accordingly to get the water level correct inside the pipes. Thanks a bunch! Will start construction tomorrow!!


Mark Ridsdill Smith August 21, 2013 at 9:49 am

Hi again, sorry, I’m not sure I totally understand Jens and if you’re talking about the control tank or the water butt that is holding the bulk of your water. As the water flows by gravity, the water level in the control tank will always be the same as the level of the water in the reservoirs. If you lift the control tank higher, the system won’t work. The water butt does need to be higher than the control tank. But I can’t think of much benefit of it being more than a few inches higher as all it needs to do is flow, and I don’t think it needs much pressure. My water butt was literally just a few inches above the control tank and water always flowed in without any problems at all. Does that help?


Jens August 20, 2013 at 4:48 am

Sorry, one more question: what happens when it rains heavily? I live in Thailand and sometimes we get huge showers for hours during the rainy season. Maybe add some overflow protection by drilling holes along the edge at the top of the box? Or do you reckon this will drain itself as is? Thanks Mark :)


Mark Ridsdill Smith August 20, 2013 at 7:26 am

You could make more than one overflow hole, and also put lots of large drainage holes in the corrugated plastic. That should be enough. However, if you still have problems, you could always mulch the top of your containers with plastic sheeting so that the rain runs off.
Very good luck with your project, would love to hear how it goes if you get a chance.


Jens August 20, 2013 at 4:43 am

Hi and thanks for this lovely guide. I just have one question before I start constructionist this: what is the corrugated plastic resting on? To me it would seem that when you fill the box with soil after everything is done the plastic sheets would give after and bend and destroy the construction? Those sheets are very light and bends easily, no? Thanks for a reply!!


Mark Ridsdill Smith August 20, 2013 at 7:22 am

Hi Jens, great question. The plastic is held up in two ways. First by the wicking feet. The holes I cut in the plastic are just slightly smaller than the wicking feet – and so the edges of the plastic sit on top of the wicking feet. (Even if your holes in the plastic are larger than the wicking feet they would still offer some support when attached firmly with cable ties). Second by a ridge of wood I screwed to the sides of the box, specifically to support the edges of the plastic. You can also double up the plastic, using two layers, and this confers quite a lot of extra rigidity, particularly if have the grain in the plastic in one piece running one way, and the grain in the other running perpendicular. Hope this makes sense?
Using the above, I’ve now used my boxes for four years and the plastic is still in good shape, despite the boxes being emptied and filled several times and moved on three occasions! As recycled materials vary so much, however, it may be that you have different sort of plastic – so it is possible that you may need to add some other support, short wooden legs for example inbetween the corrugated plastic and the base of the container.


diane April 28, 2013 at 1:48 pm

I would like to see you take the same idea further . An outdoor shower that refilled itself and was always refilled with tap water .Cuts high costs of hot water heaters.. esp. used in the summer months. Thanks love your idea…


Eugene April 8, 2013 at 8:27 pm

Great post!
I’d love to get your optinion on using pallet bases and landscaping fabric/tarpaulin (add in a watering system of your choice) to make herb gardens for vertical growing. I’ve not see you mention them but the principle sounds great! There’s some info on

The other alternative, for a larger volume, is to double up 2 pallets facing each other, take the middle support beam out and create a pouch of sorts. Then fill up with compost and cut slits where you are going to plant.

With that provide enough space for the roots for bigger plants like tomatoes do you think? And are there likely to be problems with rot if the wood is touching the soil directly?



Mark RS April 8, 2013 at 8:43 pm

Hi Eugene
Thanks, glad you liked it!
I’m intrigued by the pallet idea although I’ve always been a little worried about how easy they are to maintain and water. I’ve noticed that most of the images on the web are of pallets just planted and its rare to see one a few months down the line :).
But, I really do like the principle of the idea and plan to do some experiments of my own this year so that I can comment from the basis of actually having some experience of them! I’ll write about it on here later in the year, I hope.
In answer to your other q’s. Yes pallet wood exposed to soil directly will rot reasonably quickly – but hopefully should last a couple of years. You could, of course preserve the pallet with a food safe preservative like linseed or Osmo oil, depends on how much time you have to invest, I guess. Two pallets together should provide enough soil to grow tomatoes, I guess.
Does that help answer your q’s?


Eugene April 9, 2013 at 1:28 am

Thanks for the reply.
Yes very useful, since I want to make it low maintanance then I need to treat the wood then. THe watering shouldn’t be that much of a problem I’d think as I’ll have a drip + moisture sensor. Will try when I can and let you know how I get on!


Mark RS April 9, 2013 at 8:02 am

Great stuff, would love to hear how you get on Eugene – the watering system you have in mind sounds very interesting. Very good luck with it! Mark


Eamon O'Keefe February 8, 2013 at 11:29 am

Great Work Mark!!! I am highly impressed. I work as a plumber and heating engineer ( and I am constantly searching for such innovative ideas to provide something extra to my clients. I am definitely going to try this first and then I will provide it to my clients. Thanks a lot mate!!


Mark RS February 8, 2013 at 11:53 am

Great to hear you like it Eamon. Would love to hear how you get on. If you start offering it to clients do let me know – I might be able to put a few people your way!


Sarah February 1, 2013 at 4:56 pm

Wow, thanks for the info! I will definitely ask the landlords for permission to do this. I’m gonnal wait one or two months, though, until I’m not that broke anymore. :)

First project will be the wormery, which, apart from the worms themselves (I know no one who will give me some for free -or maybe I’ll try another internet search), will cost me near to nothing.

I’m quite excited about this all! Thank you so much for your website and patient advice. I’ll be back with more questions soon, no doubt..



Sarah January 31, 2013 at 12:20 am

Hi Mark, thanks for your advice. It’s good to learn you made the same mistakes in the beginning. So there’s some hope! 😉
Our downpipe is just running through to the balcony under me and forth. Water butts have to be placed under the the pipe and that’s not possible -or is there another way?


Mark RS January 31, 2013 at 2:03 pm

Hi Sarah, if you can access the downpipe you can attach a water butt diverter to it – this will divert water into your butt until it is full. A quick google came up with this pdf from B&Q showing you how: Of course, if you decide to go ahead, you’ll need to be confident there is a place on your balcony that can support the weight of your water butt.


Sarah January 30, 2013 at 3:29 pm

This looks great. I’ve read a blog about a permaculture-like garden and the blogger stated the idea that things that take great effort to establish once are often those that need practically no effort from then on. Your watering system seems to be a great illustration of this idea.

Now to my question: It looks like you catch the rain water to grow. That’s a big issue for me right now, cause my balcony has a roof, so the only rain that gets there is that which is blown over by the wind and I haven’t come up with a good idea for catching enough of it to make this worthwile. So I’ve been watering completely from the tap although I think that’s quite stupid when there’s free water from the sky which costs no energy or money to get to me and is probably better for the plants, as our tap water is pretty hard.

I’ve started growing on my balcony two years ago, but the results haven’t been too good yet for, I guess, several reasons -like inconsistent watering, lack of fertilising, lack of big enough containers for my plants and lack of protection from the wind and cold which can be a bit mean at the height I’m living.
For this year, I’m planning to be a bit more systematical with my growing, for example I wanna try out a worm compost so I can give my tomatoes what they need without buying the industry stuff.

Do you (or other readers) have any idea for me for catching rain water more effectively (alternatively for saving water)?

I wish you all a good growing year 2013!


Mark RS January 30, 2013 at 8:38 pm

Hi Sarah

Nice to hear from you – I did all the same things, using the wrong sized pots and not fertilising, when I started growing. Trying worm compost is a great idea.

With the water – the easiest thing would be if you can find a downpipe you can attach to a water butt, that’s how I collected water on my balcony. Is there an accessible downpipe running down from your balcony roof? If so, that could be your solution.



Wynfrith January 29, 2013 at 7:20 pm

I would like to know if the water sits in the bottom of the pans all the time. I would think this would lead to root rot. If it is cycled somehow, I do not see the mechanics in the designs. The tank ball would refill when the buckets ran out of water, but there seems to be no cycling of the water. More information would be appreciated.


Mark RS January 29, 2013 at 9:23 pm

Yes, the water is constantly in the reservoirs – but because only a small portion of the soil is in contact with the reservoir the soil in the container does not get waterlogged. From my observations, the roots seem to like this set up, growing down to reach the water – and I’ve never seen any rotting. The water constantly passes through the reservoir – as a hungry tomato plant will drink a gallon of water a day on a hot day. It’s a good idea to drain the system completely over winter (when the water could stagnate) and fill it again in the spring. Does this answer your questions? Please get back to me if not.


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