I've been meaning to get a food garden going for awhile but the thing is, I have a bad habit of forgetting to water my plants. It turns out, that's a key factor in successful gardening. Who knew?
Fortunately, my sister told me about sub-irrigated planters! Where extra water is stored beneath the soil (you'll actually be using a soilless mixture but that's a mouthful to say) and wicked up through the soil mix. Not only would I have to do less work but the whole system is way more efficient and less wasteful than watering your plants the traditional way.
Indeed, I did not have to water any of my 3 planters all summer! Even when it was a scorcher out and the lawn look parched, my plants were thriving in their little sub-irrigated planters!
Step 1: Explanation of Materials
This Instructable will make 2 sub-irrigated planters since 1 water tank makes 2 planters. Here is a breakdown of the things you'll need and why. It'll give you some creative wiggle-room to make improvements or adjustments to fit the material and needs you have!
- 1 IBC (or the like) water tank
Cost: I found plenty on Craigslist for $100 or less.
Purpose: They're food grade, won't rot and are a good size for a planter (~3.5' x 4')
- Drain Pipe
I could only find them in 100' rolls which would be too much if you were just doing 2.
Cost: 100' roll is about $40 new but again, you can generally find used on Craigslist.
Purpose: This will create a reservoir on the bottom of your tank where water can sit but the dirt stays out. Putting the drain pipe on the bottom gives you about 4" for the water to store up which worked fine for me! You could add another layer of drain tile to make a bigger reservoir and therefore have less dirt to fill.
- Landscape fabric
Cost: ~$10 for 3ft x 5ft roll
Purpose: You want to make sure the drain pipe stays permeable; that the holes don't get clogged with dirt. So we'll wrap the lengths and cover the ends with the fabric. If you happen to get drain tile with a sock, that's good too but it is typically twice as much as regular drain tile and you'll still need to cover the ends with landscape fabric.
- Fill Tube: PVC pipe
Cost: ~$2.50 for 1" x 2'; you'll need 1 for each sub-irrigated planter you plan to do
Purpose: This is going to be your fill tube. It'll go from the bottom of your tank to above the dirt. You'll use it to fill the reservoir with water when your planter has used all its backup water and needs more. You can use any piping you want here, just make sure it is food safe. I found these to be particularly useful as my hose fit right into it so I didn't need to hold it!
- Drainage tube: Flexible vinyl tubing
Cost: ~$2.50 for 1/4" x 10'
Purpose: This is your drainage tube. When the water gets above your reservoir, you want it to drain out instead of making your soil mixture a soggy mess. 1/4" worked fine for me but you could go a little bigger.
- Sawzall (reciprocating saw)
- Level (not essential)
- Hole Saw with diameter to match the pipe you've chosen as your fill pipe
- Drill w/drill bit the matches the diameter of your drainage pipe
Step 2: Tank Preparation
- Cut your tank in half
With your reciprocating saw, cut all around your tank. Be sure to wear the proper eye, hand and ear protections! The metal grate is definitely sharp after you cut it.
Think about where you want your half-way to be. The height of the actual plastic tank is less than the whole contraption which has a thick plastic base. If you cut it in half using the total height, one container will be deeper than the other. If you cut it in half using just the plastic tank measurement, your contain depth will be the same but the actual height of the half with the base will be taller. It really doesn't matter but something to think about if you have a specific look you're going for.
> Tip: Draw a guide line all the way around! I tried to eyeball it on my first tank. It shows...
- Level your tank
Place your tank where you want it then check if it is level. This is tricky because the bottom isn't exactly flat and even if you have a long level (or use a 2x4/level combo) across the top, your cut is likely not 100% straight so that'll throw it off. Just aim to get close. You don't want your water in the reservoir to be angled so much that the water doesn't reach the drainage tube or reaches it too soon. My yard is on a hill so I had to do some extra work here.
Tip: Wherever you place your tank, make sure you're happy with it. Once you fill it, it isn't going anywhere!
Step 3: Drain Pipe Preparation
- Cut your drain pipe to length
You'll be using your reciprocating saw again, cut 5 pieces of drain pipe that fit the width of your planter. The tighter you make the fit, the better. This will help to keep dirt out of the ends.
- Cut your fill pipe hole
Using your hole saw (the diameter should match your fill pipe diameter for a snug fit), drill one hole into one of the drain pipe pieces. It should be a few inches away from the end of the pipe so you don't accidentally split the plastic. You'll only need one drain pipe piece with a hole per planter.
Step 4: Fill Tube Preparation
Cut your fill tube
Using your reciprocating saw, cut the fill tube to length at an angle. The angle will make it so it won't sit flush upon the bottom which would block the opening when you're trying to fill it.
Each planter gets one fill tube that goes in the hole you created in the drain pipe with your hole saw. You want the fill tube to go from the bottom of the planter to well above the top of the dirt. Say about 6" (I got a little excited and mine are more like a foot which is pretty overkill).
The tube needs to be free from debris and you don't want dirt splashing up and into it. You can put a cover over it if you'd like.
Step 5: Reservoir Preparation
- Cut the Landscape Fabric
Now we have to make sure no dirt can get into the drain pipes through the ends or through the perforated holes throughout.
Roll out some of your fabric and see how much you need to wrap around a piece of drain pipe. You'll want it to overlap a decent amount to stay in place. I think mine wrapped almost twice around. You could also use zip ties but I didn't have any and was too lazy to get some so I opted for rolling the drain pipe twice.
You'll also want the fabric to be longer than your pipe on either side so you can use it to cover the openings. Depending on the length of your drain pipe, you could fold the fabric hamburger style instead of my hot dog style shown in the photos.
> Tip: Now matter which way you fold it, fold all the layers you need before cutting. It'll make the pieces uniform in size and it'll make it so you can get all 10 of your pieces in just 2 cuts! 1 to cut from the roll and another on the fold lines down all the layers. Very exciting :)
- Wrap the Drain Pipe
With your cut pieces, you can now wrap each individual drain pipe.
Ideally, the landscape fabric will be longer than the drain pipe so you can fold it into or over the opening (instead of having to cut a separate piece for each end and use a zip tie). I folded my fabric over the holes and squeezed them into the tank. My drain pipes fit snug against the edges so I felt the fabric would be secure enough to keep dirt out.
> Note: If you got drain pipe with a sock, you only need to cover the ends as your drain pipe body is already protected!
- Fit the Fill Tube
When you get to the drain pipe that has the hole in it, wrap it like usual. Keep the fabric taut over the hole, stab your scissors through the hole and then make little slits in the form of an "X". You don't want to make the hole too big because you want the fabric to help seal that hole off. With the angle part of your fill tube, slide it all the way into the hole until the point hits the bottom.
- Place the drain pipes in the tank
You've done most the hard work! Now you just need to place the covered drain pipes into the tanks. If your drain pipes have a little curve in them, pack them in with some of your soilless potting mixture around them to keep them straight but don't cover them up just yet!
Step 6: Drainage Tube
- Drill Your Tank Hole
You'll be working on the opposite side from the fill tube in the opposite corner. So the fill tube and the drainage tube are diagonal from each other. With a drill bit that matches the diameter of the flexible vinyl tube, drill a hole directly above the top of the drain pipe.
- Drill Your Pipe Hole
With that same bit, drill a hole into the drain pipe. To prevent the landscape fabric from twisting around the bit, you'll want to make a little cut in the fabric first. You don't want it to be too big because again, you want that fabric around everything!
- Fit Your Drainage tube
Take the end of your vinyl tubing and push it through the hole on the outside of the tank and pull it into the tank. Pull enough of it in to reach the hole you made in the drain pipe with a couple inches to spare. Now push that end into the drain pipe for an inch or two. If some of the fabric goes into the hole with it, all the better! It'll make it fit snug and help keep dirt out.
Now cut the extra tubing on the outside. You'll want to leave a couple inches so it sticks out nicely for drainage. Mine is so long in the photos because I may build something around it to 'pretty' the tanks up and wanted to make sure I had enough slack.
Step 7: Test Your Planter!
Before we go any further, you want to make sure everything is working the way it should!
- Fill up your tank with dirt just so it covers your drain pipes. This will help them stay in place but they will rise with the water. You could also put some 2x4s or something heavy on them to help them stay put.
- Put your hose in your fill tube and start filling your tank up! Your goal is to fill it just past the drainage tube exit hole to ensure your tank drains properly.
Things to check:
- Fill tube
You want to make sure the water is going down the fill tube and filling up your tank, not back up at you. If it does come back up at you, something is obstructing the water and not letting it flow out. Is your angle steep enough on the bottom of the fill tube?
- Drainage pipe
It'll take some time as the water level has to rise above where your exit hole is but you want to make sure that once the water reaches that level, your drain tube starts draining! If it isn't, check to make sure the tube isn't pinched or obstructed.
Step 8: Fill Er' Up!
Once you're satisfied with your sub-irrigated planter's fill and drain pipe, it is time to fill up!
Remember to use a soilless mixture!!! It is absolutely key as a soil mixture will be too heavy and won't wick the moisture up to your plants. Mine was a mixture of pine fines and a composting mix that my local landscape business recommended.
Once your planters are full, you want to fill your reservoir up with water if it isn't already. I'll be honest here, I only tested the first planter, I felt pretty confident about the other 2 so I didn't fill the reservoir until the planters were already full of dirt. Again, fill the reservoir until your planter starts draining. Now you're ready to plant!
> Note: I only did one layer of drain pipe which meant I had to use my mixture to fill it up. I was worried about my plants having enough space. My sister did 2 layers of drain pipe and her plants did just fine plus she used half the soilless mixture I did. Again, both worked fine but if you have extra drain pipe or extra soil mixture, one might work better for you.
Step 9: Planting and Other Final Touches
Depending on the plant, I did 3-4 rows in each of my planters. I started some from seed and some from plants.
Mulch around all the plants to help protect the soil mixture from drying out and the plants' root system. If you're starting from seed, wait to mulch until they've popped out of the ground.
The height of the planters keeps rabbits out but does nothing to deter the damn squirrels. I had some extra furring strips which I just cut to size and slid between the tank and the metal cage. Draped it with some bird netting and had no squirrel issues all summer!