How To: Make a Self-Watering Greenhouse (In-Depth Tutorial)

I know it seems a little redundant to post this when I've already posted a video, but it is kind of hard to get more than a vague idea from the video alone. I hope this sheds a little more light on the subject. I'm sure it also seems like I'm beating this idea to death, but this one concept opens doors to further innovation. After I finish this article, I'm going to put another one up that shows a hinged, raised bed house and talk about some amazing things you can do from there.

Once the foundation of principles is laid, and with input from the community, I'll shed more light on the whole concept that I'm trying to push here. I want to see an open source, self-contained plant habitat that can be entirely controlled from an iPhone. I want to have full watering, nutrition, lighting and heat in a self-contained device, and I want it to be a wide open concept that anyone can use. Rather than becoming a manufacturer, I just want to see this happen. I think it'd be cooler if anyone could do it.

Yes, that is done in the shop, and yes, that's a weird environment to build a greenhouse.  I do my materials prep, cutting and dry fitting in the workshop because I have every tool I might possibly need at my disposal. In truth, you don't need many tools to get this done.

Tools You Will Need

1. Something to cut the pipe: Ratcheting pipe cutter, hand saw, band saw, compound miter saw, etc.
2. Measuring Tape
3. Marker for cut lines
4. Something to bend the pipe. I'm using a 9' PVC Bendit, but you can also use a heat gun, blow torch (not recommended), car exhaust (not recommended), heat blanket, infrared heat box, etc.
5. Cleaner, Primer and Cement
6. Drill, Tap and Deburr tools to insert spray nozzles

(optional) Mallet

PVC Pipe is cheap no matter what gauge you use. I strongly recommend you use the largest diameter appropriate for the size of greenhouse you are trying to build. The thicker walls on larger pipes allow more surface area for the threads on the spray nozzles to grip. Bearing this in mind, even a large greenhouse with thick pipe should still be less than 200 bucks. A small hoophouse should cost you less than $50.

Materials You Will Need

1. PVC Pipe in the gauge appropriate to the height of your greenhouse. Bigger houses take bigger pipes to last longer than a few years.
2. Tees for the first and last ridge pieces as well as for the feet of every individual rib.
3. Crosses for the ridge pieces that are not at the ends.
4. (1) 4-way fitting and the fitting that connects to a garden hose.
5. (3) 3-way fittings for the other three outside corners.
6. Sheathing material such as polycarbonate, corrugated plastic, clear vinyl (pvc sheets), polyethylene, etc.
7. Snap clamps and zip ties to attach the sheathing material to the frame without puncturing the pipes.

In order of assembly:

Step 1 Draw out a simple plan so you can get a proper fitting and piece count. 

Yes, I did misspell rigidity.

Step 2 Determine the exact height and width that you want.

Length will be dealt with by the number of ribs you have on the greenhouse. Divide your width by 2, and that will give you the run number for every arc.

Step 3 Draw the curve out.

This will need to be done where you will be setting up the form for duplicating your rib pieces. If you make height equal one half of the width, then you can just use a large sized compass to draw out a circular arc.  Make sure your arcs complete a perfect 90 degree curve (unless you want to do something a little more intricate - the sky's the limit!) for easy fitting, or at least make sure you have a strategy for achieving the full 360 degrees to get around the loop.

Step 4 Glue pieces of PVC .

The pieces must be one size larger than the pipe you are trying to bend down on the arc you've drawn. This will serve as your form. In this case, I was able to use the grooves in the concrete to determine the 90 degree curve.

Step 5 Cut pipes to an appropriate length so you won't have too much waste. 

You can use the straight cut-off pieces on the ridge beam and the sole plates of the walls. It helps to do a test bend first and then see how much you can safely cut off.

Step 6 Heat up the whole length of the pipe. 

The tool that I'm using here is definitely the easiest way I've found to do this. There are other methods out there, but with a nine foot bender, you can heat nine feet of pipe evenly at one time.

Step 7 When the pipe is evenly heated, place it into the form.

Begin heating your next pipe. If you smooth the piece into the form, you will exactly duplicate the shape you are looking for.

Step 8 Mark the pipe for cutting when it has cooled. 

If you are using an in-pipe heat bender, by the time one piece is cooled, the next one will be ready to bend. In this case, I'm using the groove in the concrete as a marker so I put my cut lines in exactly the same place on every piece.

Step 9 Once you've made all of your bends, cut the excess off of your pieces. 

It is nice to mark and cut instead of trying to cut your pieces to the exact length before you do the bend. You do want to cut the major excess off before bending, but it helps to leave a little just to be sure everything is the same at the end. I'm using a band saw here, but you've definitely got options on what you use.

Step 10 Cut all of your ridge and sole spacers.

They should be about 22 and 5/16" so that your ribs land 24" on center. Larger diameters of pipe will have smaller spacers, so be sure to check what actual length you need. The advantage to 24"centers is that most sheathing materials come in 4'x8' sheets, and this makes it so you don't have to cut them to make them center on the studs. Get all of your pieces except for the end spreaders together and prepare a space to dry fit. The number of pieces will vary based on how long you want your structure to be.

Step 11 Dry fit all available pieces.

You can now measure from inside to inside on your ends to make the spreaders/drain connections for the bottom.

Step 12 Cut and dry-fit the spreaders.

I ran out of pipe today, but I will upload a picture when I get a few more sticks, and I'll show how the hose interface hooks up as well.  It's all pretty intuitive, and you should be able to figure it out, but I'll show it as soon as I have my materials in order.

Step 13 Drill Holes with tap and die.

Fit watering nozzles into them.

Step 14 Take apart the joints, one at a time, and clean, prime and cement them.

Allow the cement to cure for at least two hours and then reapply it to the outside of all joints.  If you are completely confident that you cemented every joint perfectly, this is not necessary, but it does save you from coming back and recementing any leaks.

Step 15 Allow this cement another two hours to cure.

Remove all nozzles, and flush the system for at least twenty minutes. Re-insert the nozzles, and the watering system and framing are ready to go.

Step 16 Apply sheathing.

Use snap clamps along the sole plates and zip ties at the ridge and along the studs (ribs). In further installments, I'll show how to use PVC pipe to make the end walls and even a door. You can also use wood to stud up the ends, but I like to use PVC for the consistent look on the finish.

Tips

• Hot bending PVC is the best way to produce a bend because once it cools, it retains the shape perfectly and goes all the way back to its original hardness.  There are a lot of plans that show cold, tension bending, and they are great, but they are almost impossible to integrate watering into.  When PVC is heated, it takes on the consistency of a cooked spaghetti noodle, and it can be easily formed into any shape.
• If you want to get serious, use at least 2" pipe, and be sure it is the UV resistant type.  After cementing the structure together, put the sole plates of the walls into a concrete footer.  Be sure you can still connect and disconnect the hose, and make sure you can drain it when the cold comes.
• If you have the means, you can put the sole plates of the walls into the outside trenches of a concrete floor.  If you integrate radiant heat into the concrete floor, you can use it all year long.  As long as you don't let water freeze inside of the walls, even the self-watering function can be used through the winter.
• This article will be completed very soon, I just ran out of materials today.

Warnings

• PVC pipe can release harmful toxins when overheated.  Be sure to heat only to the minimum temperature necessary for the malleability you need.