This is some information I read about this style of growing.
*** DIY SIP Designs ***
For those interested in building their own SIP to experiment with I thought I'd offer some simple design options. Keep in mind there are several different ways to build these things and I've tried a few and they all seem to produce about the same end result: great plants.
There are a few simple design principles that all of the various designs share, and essentially those are soil above, a water reservoir below and an air gap in between, and typically a fill tube to allow you to by-pass the soil to fill the reservoir. How those things are accomplished is up to the builder. I make the air gap/water reservoir by establishing a void in the bottom of the container that soil is packed densely around which forms the wicking mechanism to kept the rest of the soil in the pot constantly moist, but on a bit of a gradient, wetter at the bottom, less so as you move up the pot. This is similar to what is found in nature since water drops in the soil due to gravity so there is usually more water the deeper you go.
I've built them in various sizes ranging from Solo Cups, to 1L take-out containers, to 2 and 5 Gallon (8 and 20L) buckets and up to 17 gallon (65L) tubs. Here's how I do them:
This version is a bit of a compromise since creating the void is hard to do with such a small container so it's built a bit differently than the others.
For this size I make a small hole with a soldering iron or drill bit about 1 inch/25mm up the side from the bottom of the cup.
Then I put either small hydroton clay balls or perlite/pumice in the bottom up to a level about 1.75"/45mm and then top with soil. Since the hydroton/perlite layer is higher than the overflow hole, there is a bit of an air gap satisfying the design requirement. There is not as much air as in the other design options, but as I said, this one is a bit of a compromise.
Given the lack of real estate to work with I don't even bother with a fill tube, but rather water by sitting the solo cup in a slightly larger tub of water to fill the reservoir from below through the overflow hole. I usually put a second hole slightly above the overflow hole which seems to assist with filling the reservoir more quickly by allowing a vent for the air being displaced by the increasing water level.
That's it. If you use clear cups you'll be able to see the roots develop but be sure to slide it into an opaque cover cup since the roots won't develop as well if exposed to light.
1L Take-out Container
This is probably the smallest size I would take to flower but is large enough for a respectable harvest (relatively speaking).
For this one you'll need two containers. The first is the 1L container and the second is some sort of small food grade plastice cup/container where the diameter of the rim is slightly smaller than the bottom of the 1L container. I use small single serving applesause containers that fit perfectly. This will make the reservoir void by making a bunch of small holes in it and placing it upside down in the bottom of the 1L container.
I make an overflow hole in the 1L container about 1 inch/25mm up from the bottom but make sure it is at least 1/2"/12mm below the height of the cup that makes up the void to ensure I have an air gap. Up to double that amount is preferable.
Then I make a bunch of small holes in the smaller container (I use a soldering iron) and place it upside down in the 1L container. Put your soil mix in so that it surrounds the inner cup but try to leave a void between it and the overflow hole to help with air flow. I've built this size both with and without a fill tube so that's a preference decision.
Be sure to pack the soil around the inner cup firmly to help with the wicking process, but fill the rest of the container with soil firmed like you would for a normal pot.
2 Gallon/8L or 5 Gallon/20L Buckets
Same basic design as the 1L version, just larger containers. I get my buckets from Lowes in the States because they are a deep, dark blue which helps shade the roots from light better than lighter or white colored ones.
For the container that creates the void I've used food grade plastic food containers like salad bowls or food storage containers as well as pasta strainers. Same rules here, try to find a container where the upper rim is slightly smaller than the lower width of your bucket.
I do use fill tubes for these so first I make a larger hole in the bottom of the inner container (which will be on top when we flip it to install it) that is slightly larger than my fill tube. I use the white PVC plumbing pipe (1/2"/12mm) and make my hole with a 7/8"/22mm hole saw which is the outer diameter of the pipe.
I actually make two holes, one each on opposite sides of this inner container. Then I use two fill tubes with the idea that there will be a better chance at air flow with this set-up than there would be with a single entry to a cave-like void you'd get with a single fill tube. No science to back this, I just feel like it is a better design.
I also like to have my fill tube stop just after entering the void to ensure air flow even when the reservoir is full so I cut off a small stub piece from the fill tube and attach it back with a coupler which holds it up when installed since the coupler is a larger diameter than the pipe and won't fit through my hole. ResDog has his fill tubes bottom out in the reservoir but makes holes all along its length to accomplish the same thing.
Then I make my overflow hole in the outer bucket making sure it is at leat 1"/25mm below the top of my void container for the air gap, and then make a bunch of small holes in the inner container to try to maximize air and water flow from this inner cup into the surrounding soil. I also make holes on the bottom (what will be the top) of the inner cup to get air to the roots once planted.
Then fill the pot with your soil mix and be sure to pack the soil around the inner cup firmly to help with the wicking process, but fill the rest of the container with soil firmed like you would for a normal pot.
I use a funnel I cut from the top of a water bottle to make pouring water into the fill tube a bit easier. I use a plumbing fitting (called a bushing) to attach a 1" coupling to the 1/2"pipe and the neck of the bottle slides into it nicely. I'm right handed so I like to position the fill tube just to the right of my overflow hole. This makes it easier to watch for run-off as I'm filling the reservoir than it would if it were on the oppositie side of the bucket.
17G/20L Plastic Tub
This design is a bit different from the buckets. The tubs I used for my outdoor vegetable garden are rectangular and I use perforated landscaping drainage pipe layed flat to make the reservoir/air gap. I used 3 sections of 4"/100mm pipe that fit perfectly laid side-by-side but 2 sections of 6"/150mm pipe would work just as well and give you a larger reservoir.
I capped the pipes off with the cover that came with my 1L containers to keep soil out of the pipes. I cut the cover slightly so it would snap between the ribs of the drainage pipe. Then I made my overflow hole about 1"/25mm below the top of the pipe.
Next I installed a 1"/25mm fill tube by cutting a hole in one of the pipe sections and then filled around the pipes with my soil mix being sure to pack it well around the pipes to ensure good wicking. The rest of the tub was filled with my mix firmed like I normally do.
-Or- If using cloth pots, you can simply lay them on the soil that covers the pipes. I'd probably put a good inch or two of soil over the pipes to account for any settling, although there shouldn't be much of that if you've packed it well.
So, that's about it. pretty simple but very effective.