Hanging It All On The Line

Why build support posts when you can use a super-strong dome?!?!




I needed to come up with a way to support and spread out some of my vine plants in the greenhouse. By removing a nut on the hubs and installing a coupling and eye bolt, it is an extremely strong point for attaching a cable system to act as a trellis.

Installing it is very simple, loop the cable through on one end and clamp it, feed it through another eye bolt on the other side of the dome, and bring it to another eye bolt to figure out the final length.  On this end, I loop it through a turn buckle.

Alright, moving right along….

Then just hook the turnbuckle into the last eye bolt and tighten the cable.

All that is left to do is to tie the plants on to the cables.  I also run some twine down to the grow beds so that the cucumbers can grow up it and attach to the wire.  Here’s a shot of the tomato and cucumber once they have really started to grow along the line.

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Theft!

Hello to all my friends!

A follower has let me know that he saw one of my videos posted on another user’s YouTube channel.  I greatly appreciate the fact that they brought this to my attention.  I am always happy to produce and post videos which are always free for you to enjoy.  What I don’t like is some scumbag ripping and reposting my videos under their own channel.  It probably won’t be a surprise to you, but I am a YouTube partner and do receive some ad revenue from my videos.  (It’s very little, but every penny helps!)

If you happen to see one of my videos posted, and it’s not from the Web4Deb channel, I would be very grateful if you notify me of this theft.  Thank you for your support and I look forward to providing more videos in the future.

-Rob Torcellini

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Dipstick

I forgot to include a few video clips in "Aquaponic System Install - 3 of 3" so heres a mini-video about a dipstick. ;-)

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Building a Geodesic Dome Greenhouse Part 3

Finally got around to doing the third video in my series of building the geodesic dome.  This one covers how all the struts are made.  Its filmed in HD so you should be able to expand it to full-screen!  I hope you enjoy it!

Below is the transcript from the video....

Hello Everyone,
This is the third video in the series about building a geodesic dome greenhouse.  This time I will cover how to build the interconnecting struts which are made from red cedar.   I choose red cedar because it is rot resistant.  You could use treated lumber, which is substantially cheaper, but I was concerned about chemicals leaching into the water for my aquaponic system.

The site I used for the calculations is acidome.ru.  The entire site is in Russian, but Google Translate does a fairly good job converting the text.  The calculator lets you enter the diameter of the dome, choose the hub type and size, and even the dimensions of the struts.  It will then calculate the angles needed at each hub and also calculate all the various sized struts and labels them with the dimensions taking into consideration the size of the hubs.

The best feature is the ability to have the software calculate a flat base, since a 3V 3/8th dome is not flat.  One click and the struts are recalculated with the proper lengths!

With a 33 foot diameter 3V dome, each triangle will never be wider than 6 feet.  This will allow me to purchase the polycarbonate glazing in 6 by 24 foot sheets, helping to minimize the amount of scrap.

The struts are made from red cedar 2x4’s by 14 feet.  This will be enough material to cut 2 struts from each board with some scrap.  The end of each board is cut at a 12 degree angle so it will align with the hub.  Not every hub connection is exactly 12 degrees, but there is enough flex in the structure for the angles to average out properly.

Once the struts are cut to length, they are run through the table saw to add a slight bevel to them.  When the dome is fully assembled, the polycarbonate panels will rest fairly flat along the bevel.  This will also insure that the height of each strut is the same since it can vary slightly from the mill.

Next I remove some of the material from the end of each strut using a dado blade mounted in the radial-arm saw.  This space will provide an area for the top tab of the hub to rest and provide enough clearance for the polycarbonate panels over the crown of the carriage bolt.

I built a jig to act as a stop and keep each strut aligned properly during drilling.  This allows for a consistently placed hole to be drilled near the end of each strut.  The placement of this hole is important so it will fit properly into the hub and provided an accurate length for the hub and strut combination.

And now, the perfect excuse to use one of my favorite tools!
The bottom of the head of a carriage bolt has a square neck so it can grab into wood to prevent it from turning.  To get it to fit into the metal tab, I would either have to drill the tab’s hole larger, compromising some of its strength, or turn down the neck of the bolt in the metal lathe.  I chose to turn each bolt and then will re-galvanize the area with cold-galvanizing paint.

Here is an example of how the final assembly will fit together.  The strut is sandwiched between the two hub tabs and then tightened into place using a lock washer and nut.

This top view displays how each strut can pivot slightly on each hub.  Since the angles of each triangle section aren’t the same from one section to the next, this allowed for me to make the same hub and allow the pivot against the bolt to make minor changes to the angles.

This side profile shows how the dado in the strut allows the polycarbonate glazing to clear the area without hitting the tab or bolt head.

Finally, this profile displays how the glazing will set flat into the beveled area that is cut along the top of each strut.

I assembled the base to verify that the calculations were correct and the pieces fit together.  So far, so good!

That’s all for now.  The next video I plan on detailing some of the site work.  Thanks for watching!

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Sequencing Indexing Valve

This is a sequencing / indexing valve that I designed a couple of years ago.  This uses a pinching mechanism to stop the flow of water.  It is able to pass solids and keep operating if there is a clog elsewhere in the plumbing.  I decided that it would be too expensive to develop and would show everyone how it works.

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7 The Coanda Discharge

The Coanda Discharge letting out below the water surface
The Achilles heel of the Bell Siphon is getting the silly thing to start.

There is an art to setting the bends in the typical 90 degree elbows of the typical discharge pipe design. If it fails to work in manner A, bend one way. If it fails to work in manner B, bend the other way. Or fuss with the rate of flow into the growbed. Or check the pipes for bio-fouling and rinse with a hose.

No wonder many people just give up on bell siphons and revert to timers!

The Coanda Discharge eliminates any need to fuss with the discharge. The Coanda Effect is that fluid likes to stay adhered to a surface even when that surface bends. It is why planes fly. It is why milk sometimes misses your cup and drips in a strange direction.

I stumbled onto the Coanda Discharge by accident. I planned to put together the kind of right-angle configuration I’d seen in videos of aquaponics systems. But I didnt have a 90 degree elbow, so I used a 45 degree elbow instead. The 45 degree elbow worked great. Because of my fluid dynamics background, I recognized why it worked so well and what it needed to be named.

When water overflows the lip inside a bell siphon, water sheets down the sides of the tube, leaving a column of air. You need to form a plug of water in a location where gravity can pull it out, sucking out the air column and starting the siphon. A 90 degree bends form that “plug” by making the water splash, but when you turn the water 90 degrees from vertical, you’re horizontal and gravity is no longer helping you.

In a Coanda discharge, though, the slug of water is formed by the stable “mounding” of the water as it encounters the pipe inserted into the 45 degree elbow. There’s little to no splashing, and when the plug of water has formed, you still have plenty of gravity to pull out that water plug and the air column behind it.

Here’s a video clip showing the difference between no elbow, the 90 degree elbow, and the 45 degree elbow cases.When the outlet of the Coanda discharge is buried below the water surface in your CHOP fish tank, the only significant noise is the burp when the siphon breaks.

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3 Setting Up the Tanks

Tanks and materials for the 365 Aquaponics System

The first thing you need to have in an aquaponics system is a way to hold water.

In order to achieve system stability and grow an interesting quantity of food and fish, you’ll want to shoot for a water volume of 250 gallons. That’s a lot of water.

There are a lot of options. Concrete ponds, International Bulk Container (IBC) totes, 55-gallon drums, wood structures lined with plastic. For the 365 Aquaponics system, I chose stock tanks.
Here are my reasons for using stock tanks.

They are an existing and proven product. Stock tanks were designed to hold water for cattle, sheep, and other large livestock. They were designed to withstand day to day abuse from such livestock and the elements in which the livestock lives. Because plastic stock tanks are rugged, large capacity, and constructed from food grade plastic, they are often used by restaurants for food storage and preparation. Perhaps most important, they should be locally available.

When you’re buying something this big and having it delivered to your home, you’ll pay a hundred dollars or more just for shipping. If you can get it in stock from a local agriculture store, the shipping to the store has already been covered by the store as part of the cost of doing business.

They require little modification, if any. Grow beds in the 365 Aquaponics System have a single easy to drill hole (1” if using ‘English’ units, 25 mm if using metric). Beyond stacking some cinder blocks and planks, I don’t need to build support structures.

So here’s a video clip showing me preparing the stock tanks for the 365 Aquaponics System.

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Awesome Aquaponics Events for Earth Week 1 of 3

Various folks are rolling out the aquaponic carpet for Earth Week. Im going to be holding tours every night, as are several dozen other aquaponics folks across the United States.

For tonight, I wanted to mention a workshop my friend, Sahib Punjabi, is putting on down in Florida. If youve seen the book, Sahib is the one who has created a garden paradise in a vacant alley behind a strip mall. Hes got everything going on down there, from floating rafts to vertical towers to media beds, including wicking beds and xeriscape-like root-zone watering of plants and trees along the verge of the parking lot.

Tomorrow Ill talk about free tours being held by members of the Aquaponics Association, but for those of you ready to move forward to some serious gardening, Sahibs workshop near Orlando, FL, is a great opportunity.

Sahib is also working with the non-profit Feed Hunger Now to train folks on how to use aquaponics to alleviate hunger, using "dead space," areas that get sun and rain but that are currently empty.

Sahibs Florida vision is very close to that of Eric Maundu, of Kijani Grows. Hundreds of thousands of people have been introduced to Erics vision of converting urban wastelands into productive gardens and farms, as shown in the video below:



A third place I know of that is working to serve the urban hungry is The Grow Haus in Denver, Colorado. Tonight Ill close leaving you with a short piece where Coby Gould talks about the neighborhood food hub concept behind The Grow Haus. Very Cool!

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Aquaponics System Designs

We constructed two separate aquaponics systems: one by the name of “Nutrient Film Technique (NFT)” and the other a clay bed system. The purpose of constructing both systems is to test the efficiency of each, which, in addition to other factors, depends on the specific plants being grown (we planted leafy greens, including tomatoes and basil). In either case, it is necessary to have a large ratio of plant-growing surface area in relation to the area in which the fish are reared, in order to prevent toxic levels of ammonia rich organic matter from accumulating. Below is an outline of each system.

Clay Bed System (Sistema de Camas de Arcilla)

            The clay bed system is the simpler of the two systems. It involves a large bed of clay pieces in which the plants are grown. Clay is used for its water retaining capabilities. Water can be run through the bed either continuously or in a flood-and-drain manner. Water reaches the bed from the fish tank through a sedimentator and collector, to separate out solid organic matter produced by the fish, and a reservoir from which the water is pumped. After running down the slightly sloped bed, the water is then recycled back into the fish tank.

Nutrient Film Technique (Sistema NFT)

NFT is named as such because of the small amount of water running through the pipes, creating just a thin film of water to dampen the roots rather than having the roots completely submerged. In order to create an NFT system, holes able to fit plastic cups must be cut in PVC pipes. The PVC pipes should not exceed more than about 10-15 meters in length in order to prevent nutrient depletion for the plants at the end of the pipes. Holes must also be poked in the bottom of the plastic cups to allow for the plants to access water. Then the cups should be filled with a water-retaining medium. In some cups, we used clay, and in others we used a straw-like medium. Upon evaluation of the system, the efficiency of these two media will be compared. Along with the medium, a seedling is placed in each cup, which is then placed in the plastic pipe. This completes the hydroponic portion of the system. To complete the entire aquaponics system, a fish tank must be connected to a sedimentator and collector, as in the bed system. This must then be connected to an additional filter, and then to a reservoir from which the water will be pumped out through the plant-containing pipes. As in the bed system, the water is then recycled back into the fish tank. The need for a filter in this system is due to the small volume of the system, which does not allow room for nitrogen fixating bacteria. This design is specifically beneficial to smaller plants, as larger root systems may not be contained in the small plastic cups and large plants may become too heavy for the pipes.

System blueprints:

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Building the Aquaponic System Part 2 of 3

This is the second video in my series on how the aquaponic system is set up in the geodesic dome.  It details how all the plumbing is done.




In this second video, I’ll show how all the remaining plumbing is installed.  I’ll start with the line that runs from the central sump tank back to the main fish tank.

The pump is a standard quarter-watt sump pump with a float switch.  Eventually this will be replaced with a 12 volt DC bilge pump when the solar system is installed.  A threaded fitting is used to connect the pump to a 1 inch PVC pipe.  The piping is rated for potable water.  Then a check valve is in-line to prevent any water from back-flowing into the sump.  Next there is a union which allows the sump assembly to be easily removed in case it needs any maintenance.  Then the rest of the line that goes to the fish tank.

Since all these lines will be under some form of pressure and are being jolted from the pump turning on and off, they are all glued together with standard PVC solvent.  Also before using the system, all the piping is flushed out to remove any loose solvent or PVC shavings that may be remaining inside the pipe.

A little Teflon tape or liquid Teflon works great for threading various pieces together.

Earlier, I buried a section of 4” pipe to use as a conduit between the sump and the fish tank.  This is how the piping and electrical will run between them.  Having the union on the pipe really made it easy to lower the pump assembly into the sump and connect it to the rest of the line.  Don’t forget that this is a temporary pump until the solar is installed, so I just let the electrical run across the floor instead of through the conduit.

At the fish tank, the line comes up and out of the ground and over the tank’s edge.  I drilled a couple of holes near the lip of the tank so that the pipe could be secured to the edge.  Then I attached a 45 degree elbow to shoot the water down into the tank.  Setting up the pipe to drain at this angle forces the water to slowly swirl and most of the solids at the bottom of the tank will eventually work their way into the center.

Here are some of the details on how the fish tank overflows into the large buffer tank.  At the bottom center of the fish tank, there’s a 2 inch to 1 inch coupling that has a bunch of slots cut into it, acting as a screen.  This allows small debris through, but not the fish.  As the water level rises above the pipe, it starts a siphon which creates a strong suction at the bottom of the tank.  Any of the sediment that has worked its way to the bottom center gets sucked up and sent into the buffer tank.  The water entering into the buffer tank flows out at an angle which creates a swirl in the tank, slowly moving the sediment to the center where the pump for the grow beds is located. At the top of the pipe, there is a 1/4” hole drilled into an end-cap.  As the water level goes back down, the hole is exposed and the siphon draws in air, which breaks the water flow.  This is a very effective method for flushing out heavier solids over using a simple overflow.  A negligible drawback is that the water level fluctuates a couple of inches.

I start the overflow installation by drilling a hole in the tank and install a bulkhead fitting that has 1-1/8” threads.  I then install a threaded to slip-flit coupling so the 1”PVC pipe will attach to the bulkhead fitting.  The pipe then goes straight down into the buffer tank and then has a 45 degree elbow to shoot the water out at an angle.

Here is the pipe assembly for inside the fish tank.  The screen is a 2” to 1” coupling that I ran over the table saw to make some slots into it.  This piece sits directly on the bottom of the tank.  The pipe comes up to a tee where one end goes to the cap with the hole drilled into it, and the other end drains out to the buffer tank.

The piece that goes to the bottom of the tank wasn’t glued into place so that I could remove it just in case something does clog it.  Also the piece with the cap isn’t glued so that I can adjust the height of where it can stop siphoning.

Once the system was established, I discovered that pellets of food and duckweed would plug the siphon-break hole.  A piece of screen over the area quickly solved that problem.

This is a view inside the buffer tank showing how the water pours into it to help create a swirl flow.  The bilge pump sits at the bottom of the cone shape sucking up any solids that eventually work their way to the bottom of the cone.

The supply lines from the buffer tank to the grow beds are 1” PVC lines rated for potable water.  To keep them out of the way, most of them are buried under the floor.  Originally, I wasn’t exactly sure where all the beds were going to be placed and didn’t want to bury these lines while building the dome.  Instead, there’s a layer of sand under the brick.  The bricks and sand are easily removed and the supply line drops right into place.  Once all the plumbing is laid down, the sand is replaced and compacted and the brick flooring is reset.

At each grow bed, the supply line comes up from the floor and goes to a ball valve, which is used to regulate or turn off the flow of water. It then goes over the edge of the grow bed and pours the water directly in to the expanded shale.

The pump for the grow beds is a 12 volt DC bilge pump rated for 1100 gallons per hour and is located in the bottom-center of the buffer tank.  It is connected to a union so that is can be quickly removed for maintenance. 

Along the supply line there is a branch that feeds back into the tank where there are a few small valves which are tapped into the line.  These are used to shoot water back into the fish tank to help aerate the water and keep it moving a bit.  The fish also enjoy playing in the stronger currents.  I’ve also place a net over the tank to help prevent the fish from jumping out….again.

Up next in the series will be the grow bed design and construction.  For additional information, please see the description box or leave a comment.  Thanks for watching!

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Free Expanded Shale Giveaway

Another shameless plug for my company...but you have a chance to get some free Expanded Shale!!!

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Building The Aquaponic System Part 1 of 3

Here is the first of three videos on how the aquaponic system is assembled in the geodesic dome.  This first video recaps some of the installation that was done during the dome construction and shows a general overview of how the entire system operates.



Hi, I’m Rob Torcellini

This video series will show you the various details about how I set up the aquaponic system in the geodesic dome greenhouse.

This first video, I’ll explain how some of the components were installed during the dome construction.  I grouped the video sequences by the component, not in the chronological order of when they were installed.

First is the central sump tank.  This tank is used to catch all the water that is draining from the grow beds and a pump returns the water to the main fish tank.

While the foundation hole was empty, I built a brick wall around the tank.  The wall leaves a gap around the tank so that it can expand and contract when the temperature changes. If this wasn’t installed, eventually backfilled dirt would crush the plastic tank.  The end of each pipe draining into the sump has an elbow to help swirl the water inside the tank, which will help to reduce sediment buildup.

Also while the foundation hole was empty, I installed a large sump tank which is used as a buffer to compensate the changing water levels in the grow beds.  The water from the fish tank drains into this tank and then pumps the water into the grow beds.  This tank holds about 500 gallons of water and has a cone bottom, allowing sediment to work its way down and sucked out by the pump.

This tank also has a block well-housing built around it to protect it from getting crushed.  This is a view of the central sump and buffer sump wells while they were being backfilled.

There is a network of drain pipes that are buried under the floor.  These are used to collect the water from the assortment of grow beds that are throughout the dome.

The drains are 2” lines and are set at a slope to drain the water into the central sump.  There are extra drain inlets that come up to the floor which will not be used, but at the time I installed this, I had not decided on the final layout of the grow beds.

All the pipes are backfilled with sand to protect them from damage. This allows me to easily dig them up if any maintenance needs to be performed.  After I lay down the final floor, the drain pipes are cut flush with the floor.  If any dirt or insects fall into the pipes, they will just get flushed into the sump tank.  Here is the final view of the drain pipes with the central sump tank.

The last component is the main stock tank.  This is placed in the northern section of the dome to help minimize light and algae growth.  The tank is a scrap tank that I salvaged and it had a bunch of fittings that needed to be capped.  After leveling out the area with a sand base, the tank slid right into position.  While I was installing the drainage pipe, I buried a scrap section of 4” pipe between the sump and fish tanks.  This allowed me to run the pump and electrical lines between the two tanks under the floor. Since the tank was so tall, I wanted people to be able to easily see the fish so I installed 2 windows.

This is a functional overview of the entire system.  Water from the fish tank overflows into the buffer sump tank.  It is constantly pumped, along with any solids under the floor and into the grow beds.  The line to each grow bed has a valve to help regulate the flow.  There is also a line that feeds back and shoots water back into the fish tank to help aerate the water.

Using bell siphons, the grow beds continuously flood and drain.  The inner beds drain directly into the sump tank, while the outer beds drain into a raft system (not shown), which then drain into the sump.

There is a float switch in the sump tank that pumps the water out of the sump and back into the main fish tank.

The large sump tank is use to maintain a consistent water level in the fish tank.  Since the levels in the grow beds and central sump tank are constantly changing, that difference in volume has to be offset elsewhere.  Not only does this help with the water levels, it adds additional thermal mass to help keep the water temperature from fluctuating each day.

In the next video I’ll detail the plumbing installation.  Thanks for watching!

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Goodbye Bette!

I’m sad to say that our favorite fish died today. “Bob” was a feeder fish that was won by my daughter at a local fair from a ping-pong ball toss game about 8 years ago. Over the years he grew quickly and we discovered that “he” was a “she” so we renamed her to “Bob-ette”, or commonly “Bette”. Keeping her water clean was a challenge and is the reason for my discovery of the aquaponics world!

Bette’s first public appearance was in a New York Times article about aquaponics (http://www.nytimes.com/2010/02/18/garden/18aqua.html). She was also in one of my videos about building an indoor aquaponic system (http://www.youtube.com/watch?v=_NAiTEq9w5o). Most recently she was in a video produced by film maker Kirsten Dirksen (http://youtu.be/VBspR2p0YYM).

Building the Aquaponic System Part 3 of 3

This is the last of the series on how my aquaponics system is put together.  It details how the media and raft-based beds are designed and assembled.

This video shows how the various grow beds are set up in the dome greenhouse.  In order to maximize as much floor space as possible, all the beds are custom fabricated.

There are three media-based beds located in the center that are filled with expanded shale.  The beds use bell siphons to flood-and-drain the water which drains directly back into the central sump tank.

Along the perimeter wall, there are 2 media beds.  These beds are set higher than their neighboring raft-based beds and drain directly into them.  This method works very well since the media beds filter all the solids from the system and minimizes the amount of sediments that could accumulate in these raft beds.

I’m undecided on the last two beds and may make them rafts beds and interconnect them with water bridges, or have one (or both) be media-based beds.  It all depends on the types of crops I eventually decide to grow.

I drew a chalk outline on the floor that acted as a template for all the beds.  The frames are made from 1/2 inch black pipe that I welded together.  I’m using steel since it is very strong and doesn’t warp like wood, and is resistant to bugs and rotting.

The sides of the beds are 12 inches high, which seem to be a good depth for both raft and media growing.  Leaving for a little extra space along to top so the water and media doesn’t spill out, the growing depth is around 11 inches.

The bottoms have support braces spaced every 12 inches.  My original plan was to have the raft beds sit directly on the brick floor, but I had one critical design flaw in the dome… I ran the ducts for the geothermal out through the floor and the beds would block them.  I had to prop all the beds up on a brick so the air could pass under them.

When the steel cools off after welding, a little black rustproofing paint is applied which cleans up the look a bit.

This is one of the raft beds that was going to placed directly on the floor but interfered with the heating system.  Instead, a few bricks are placed under it as feet and the frame is set into place.

Back in the spring, my neighbor and I milled a bunch of the white pines that I had cut down from the greenhouse site.  Some of them are cut to 1 inch thick and are being used to line the grow bed frames.  I just laid them into place and let them overhang over the edge, marked a cutting line, and cut off the excess.  They lie down nicely and make a very strong decking for holding the liner.

The media bed is assembled the same way but is set on stacks of extra bricks.  The bottom elevation is higher than the top of the raft bed so that it can drain into it.

I purchased a large roll of EDPM pond liner.  It’s very heavy and difficult to work with, but is hard to puncture and is UV resistant.

The liner covers the entire bed and I carefully make sure it is properly centered so all the edges can be draped over the lip of the bed.  I did discover that it’s a lot easier to work with the EDPM if it warms up in the sun…even though it’s hot on the hands.  I just keep working it into each corner making sure that there is plenty of material to fit into the corners.  If there is a gap between the wood and the liner, it could stretch and eventually tear under the weight of the media and water.  I found it was very helpful to set bricks on the liner once I had it in position to hold it in place.

The corners can be a bit tricky.  Once I got the liner in place, I cut off some of the excess to make it easier to manipulate.  Then I could fold a nice and clean corner. It’s important to remember to make sure the edge of the liner is always going to be over the lip so water won’t leak out!

On the outer edge of the bed, I added a strip to anchor the liner into place.  The screws go through the strip and liner, and secure into the side boards.  The extra liner is cut off which makes for a clean looking transition from the liner to the bed.

The media beds have bell siphons in them.  I’m using a bulkhead fitting through the bottom of the bed for the drain.  So that the liner doesn’t get tangled up in the hole saw, I sandwich the liner under a piece of scrap board.  These boards a still somewhat damp and the saw is old and worn out so I have to keep cleaning the sawdust from the bit, but eventually I make my way through.

After cleaning the debis out of the area, the bulkhead fitting fits perfectly through the hole. It has a rubber washer that seals against the EDPM liner and fitting.  Under the bed, it has a large nut that tightens the fitting in to place.

The stand pipe and drain lines are made from 3/4 inch thin-wall pipe.  These bulkhead fittings have a 1-1/8” threaded fitting since it’s what I had in my assorted collection so they need a threaded to slip-fit coupling to reduce it to the right size.  I use a temporary stand pipe and fill the grow bed to test it for leaks.  I like to fill the beds right up to the rim to test for a worse-case scenario.  Plus it’s a great way to check to see if the bed is level and add any shims to the legs for minor adjustments.

Once everything looks good I put in the bell siphon and media guard, and the bed is ready for the expanded shale.  Since I recorded this video, I’ve changed the bell siphon design a bit, so click on the link to see these details.

This type of bell siphon uses a trap which helps it to start.  The trap assembly is screwed into the bottom of the bulkhead fitting and a section of pipe is attached to the trap and extends to drain into the raft bed.

The liner for the raft bed is installed the same way as the media bed.  It was actually was a bit easier setting it up in a larger area.  Once the liner was installed, I flooded the bed and removed the temporary holding bricks.

I’m using expanded shale for the growing media.  I just give it a quick bath to rinse off the dust, screen out some of the smaller stones, and fill in each bed, one bucket at a time.  I like using the shale since it’s about half the weight of stone and easy on the hands while digging in it.  Most of the corners are rounded over which will minimize the risk of it puncturing the liner.

Since the raft beds aren’t square, I needed to come up with an efficient design to maximize the space of the bed.  Using square rafts would never fit properly.  I design a single row raft that was tapered so they would “fan out” in a curved pattern when they were placed in the bed.  As the taper became wider, I placed the holes closer together.  For a mature plant, the amount of space per plant will be the same, it just is not a perfectly round or square area.

The seedlings will start from one side.  Every few weeks, a new batch will be added and the older seedlings will get moved over.  At first, the width of each raft is narrower than the space that the plant will need, but as it grows, I add a spacer in between the mature plants to give them a little more room.  By doing this, I can compact the new plants together without having to transplant them from a compacted raft into a normal-spaced raft.  Each bed will hold about 208 lettuce in about 44 square feet.

The remaining area can be used for seedling starting.  Currently the space works well for growing duckweed.

The rafts are made from 1” Dow blue board foam.  I made up a template so each raft was cut identical.  The template also has holes that marked the location for each hole for the net cup.  I used a 1-7/8 hole saw which makes for a snug fit for the 2” cups.  I found it was fastest to drill the hole half-way through, then finish drilling from the other side.  This left a bit of the plug sticking out so it was easier to remove from the hole saw.

I fill the net pots with a little bit of damp shale and drop in one or two seeds.  The dampness makes the seeds stick to the shale so they don’t just drop through.  The rafts push right over so the new set can be placed at the beginning of the bed.  Once the plants mature and need more space, the filler rafts can be inserted between each row.  So far, the lettuce has a good healthy root system and will be ready to harvest in a couple of weeks.

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