Thursday, July 17, 2008

Automatic Watering of SIPs, Part 1

I think these planters should be self watering. As in hook up a hose and you're done watering. For the summer.

I knew I wanted to work with one of the strengths of the SIP, its water reservoir, rather than adapt watering systems and techniques used for ordinary container or garden irrigation. While it's possible to run zoned drip lines or soaker hoses, they both have drawbacks.

What I came up with is inexpensive, has no moving parts or timers, uses a minimum of water, is easy to set up and operate, and (almost always) works. I think I've got a way to make it foolproof, more on that in Part 2. It's based on what, at first glance, seem like complicated ideas. However, most people intuitively understand what's going on, it just takes a few convoluted sentences to explain why it works.

I'm hoping that this post will draw some constructive criticism that we can all benefit from.


Why Does It Work?

The basic design has a central reservoir, in my case a 5 gallon food grade bucket (in yellow in the photo on the right), that's supplied by a drinking water hose (the white hose that comes from the bottom of the frame and splits off just above my right knee) and with its water level controlled by a Hudson valve (the valve is suspended in the bucket at the end of a 1/2" copper line). Out of this bucket run three (3) 1/2" black polyethylene tubing lines that loop around groups of planters. There are ten planters supplied by each loop. The individual planters are in turn fed by short lengths of 1/4" poly tubing that "tee" off of the 1/2" loops.

These loops aren't pressurized. Instead water moves from the 5 gallon reservoir to the individual planters via the loops by atmospheric pressure. I'm sure there's a scientific principle behind this, probably discovered by Archimedes, but I don't know what it is. So I'm going to call it the "water-level principle". The expression "water seeks it's own level" is another way of putting it.

Here's a diagram of a basic water level, typically used in construction projects.

It doesn't matter where the tubes go, as long as they're free of air bubbles, the height of the water in all three places (at the end of the dashed tube on the left, the reservoir in the middle, and at the end of the blue tube on the right) are all the same.

If you take this one step further and connect a series of reservoirs with tubes that are full of water, all the reservoirs will equalize at the same height.

Take a look at this picture. Obviously you can't see the water moving, but when I remove water from one of the containers the remaining water is transferred via the tubes until each container has the same height of water in it. Conversely, if I add water to any or all of the containers, there will be a new higher (and equal) even height.

Now pull all this together.

I know that a Hudson valve can keep the height of the water in the reservoir at a specific level. Using the process shown in the second photo, I can hold each of the individual planter water chambers at that same fixed level. Each type of plant "drinks" water at a different rate; it doesn't matter. Once the water level in a specific planter goes below the level established in the main reservoir/bucket, the siphon tubes will take water from the neighboring planter in the loop. Each successive planter takes from the one "before" it in the loop until the water is eventually drawn from the main reservoir. The Hudson valve senses that the water has fallen below the predetermined height and it opens, allowing water from the hose to fill the reservoir back to the necessary level.

That's the theory. There are some tricks to get it working.


In Part 2 I'll talk a little about that.

[ed. - Here's the link to Part 2]

13 comments:

Greenscaper said...

Bruce, it's great that you're blogging about this. It is a significant public service. Thanks!

Bruce said...

I'm glad you like it Bob.

After searching the www, I wasn't able to find a cheap automated watering system that worked with the SIP. The few that (partially) worked were very technical Rube Goldberg contraptions that seemed to be missing the point.

I'm trying to make it easier to use these containers, hoping that more non-gardeners like myself will give them a shot. If we can show that we've got a cheap, effective, easy to use way to automatically water several planters, I think we can draw more people in.

That's just part of it though. Even if I come up with the Perfect Product, it still needs to be marketed/presented to an audience that's conditioned to be suspicious and dismissive. Especially of Do-Gooders and their Crusades to Save the World.

kathy said...

When will you be posting Part 2? I want to build the Hudson valve AWS for next year. Did you use the 1" or 1/2" valve. I even did my own experiment similar to the one pictured with the containers filled with water. It helps me understand the concept. I need to know, what are the "tips and tricks" to getting the system to work smoothly. Currently I am a 1st year SIP gardener. So far I'm convinced it's the best way to grown vegetables and herbs.

Bruce said...

That's a good question Kathy.

I hope to do it shortly, within the next week.

Getting the bubbles out of the tubes is the big concern. If you don't, the reservoirs won't all equalize at the same height.

I do that by attaching a hose to the end of each tube, effectively blowing all the bubbles away. If you disconnect the supply hose and siphon tube under the surface of the water in your main reservoir, you can keep bubbles out of the lines.

I used a 1/2" Hudson valve.

Derek, another one of the contributors to this blog, has put together his own automatic watering system after seeing mine. He said he'd like to write about what he came up with.

So, with any luck, there should be a couple of posts on this coming up soon.

kathy said...

I have successfully strung siphon tubing from one of my boxes that fills (overfills) with irrigation tubing attached to a spigot timer, to another SIP that does not get direct water. IT WORKS! I am amazed at this simple yet somewhat baffling water principal. It is as if "the two SIP's have become one".

I have much more confidence now with going ahead and purchasing a Hudson valve and getting it to work. I've got half of the operation already figured out.

Thanks so much for the instructions and inspiration.

David said...

I mean to be a killjoy but, wouldn't diseases, soil pathogens spread very rapidly between SIP'S by interconnect them? it kinda removes one of the main advantages of the EB system.

Bruce said...

Hi David.

It's something that I wondered about too. What I've put together links together all the water reservoirs, and any plant diseases can theoretically spread through the shared water supply. As you probably know, the official Earthbox Automatic Watering System doesn't work in the same way. Each container has it's own regulator that allows it to draw "pure" water from the main supply line as needed.

I don't think it's a problem. When I was putting this together, I thought about how plants share all the available water in a normal garden. Diseases can spread this way, and I suppose that's one reason that certain plants are commonly grouped together. Though I think this is mostly done to bring beneficial bugs into the picture and to enrich the soil. Anyway, the shared water happens "naturally".

Another more important test: I didn't notice any unusual diseases this past year--the first year that I automated the watering. Time will tell if it holds up. There are so many variables/things that can go wrong, and adding a new technique doesn't always help.

That said, I'm happy with the watering system. It's full of trade offs and by no means perfect.

Thanks for the question; it's always nice to get feedback from other people who have thought about this process.

David said...

Bruce, I've had a few email issues lately any way...
Have you considered pruning your plants for maximum yields. Did you know most plants tend to keep growing their vegetation even while fruiting.
So consequently yields are less than 30% plus your plants grow week n lanky and can snap because of the weight.
If you pruned the lateral shoots and tips, you could easily get up to 800% production. i.e from 1 bucket of tomatoes per plant to 8.
It really depends on how determined you are to prune. It gets really crazy just with 4 tomatoes plants. Most of the videos on the net don't do it correctly, though you will get better crops with those techniques. If your interested let me know, I'll try to illustrate the technique.

Cheers
Dave

Publius said...

Bruce,

Did you ever write "Part 2"? I'me getting ready for spring and I though I would give your watering system a try.

Bruce said...

Hi Publius,

Thanks for the reminder. You'll find Part 2 here.

snarkyvegan said...

You are amazing for posting about this. I just have one really dumb question and I just can't get my head around it. If I have five 5-gallon bucket SIPs daisy chained with the first bucket going to the reservoir, and each bucket has a rigid tube going through the dirt and into the reservoir, how do I expel bubbles from the flexible tubes if they have to be inserted into the rigid tubes? If I flush them while outside the SIP, as soon as I stop, to put them into the rigid tube, they'll get air right? But I can't hold them under water within the SIP because they have to go down the rigid tube and the top bucket is already inserted and filled with dirt.

I'm sorry to be so dense but this is the one part I can't just can't seem to visualize.

Many thanks!!
Julia

Bruce said...

Hi Julia,

Good question. You're right, it's a tricky set of conditions that is hard to explain online.

Given what you wrote, it seems like you've read Part 2 to the post, so you're familiar with how to expel bubbles from the supply lines. First you hook a garden hose up to the end of the siphon line that will ultimately rest in the reservoir. Open up the other end of the siphon line (and of course all the smaller flexible 1/4" lines are open all the time). I take the 1/4" lines out of the individual rigid fill tube lines and let them sit on the roof. Turn on the water and let it run through all the pipes. It'll come out everywhere. Then close the open end of the 1/2" siphon line. Water is still coming out of all the 1/4" flexible lines. You can pick up each of the 1/4" lines and put them in their respective fill tubes, all the while the water is running--meaning no air bubbles in the lines. You can either keep the water running in the line until all the SIPs are full and water is running out their overflow holes, or you can fill the SIPs by hand ahead of time.

Then lower the hose/siphon line connection beneath the water line of your reservoir and disconnect it--while the water is still running. Turn off the water to the faucet.

I think I wrote about this with a little more clarity in Part 2, though I can't be sure right now.

Hope that helps.

glor said...

"I'm sure there's a scientific principle behind this, probably discovered by Archimedes, but I don't know what it is. So I'm going to call it the "water-level principle". The expression "water seeks it's own level" is another way of putting it."

It's called a "principle of communicating vessels" and has been known from practical experience for thousands of years.
A more formal scientific way of explaining why it works as it does is via Pascal's Law (http://en.wikipedia.org/wiki/Pascal's_law)

Hydrostatic pressure (amply measured in Pascals, btw) is equal to pgh, where p is fluid density, g - gravitation constant, and h - height of the fluid. In a closed system of two or more containers - hydrostatic pressure of the system is equalized, i.e. pgh1 = pgh2. Since p and g are constant within the closed system it follows that h1 = h2 (or the water settles at the same level in the interconnected containers).