Friday 17 February 2012

Flood / Drain Hydroponic Herb Garden ...

Fresh herbs are expensive and they don't last very long. When you're cooking a lot it means that your almost always out of something necessary ... and there's no better way to ensure a good meal than using fresh herbs. I tried conventional gardening pots, but the results were spotty. Instead I thought I try a hydroponic garden ... hey, it seems to working well for the weed industry, perhaps it could work for home cooking?

I settled on an 11-bottle Flood/Drain design. The premise behind Flood/Drain is that you flood the roots with nutrients for a short period of time and then let it drain away. Too long and you rot the roots. Too short and the plants starve. 

The entire system sits on top of a tupperware box that contains the liquids and pump. Everyday 2L pop bottles are used to contain the plants along with some rock wool to support the roots. 

The basic layout looks like this:

To ensure the parts are level, it's a simple matter of turning the frame upside down and pressing down so all the outlets are flat. This is a critical step, otherwise you'll have bottles shooting out at odd angles. Since the water and plants will have considerable weight, not being completely vertical is trouble waiting to happen.

From there, I carefully PVC cemented the parts together. You have to work fast with this stuff, it's completely unforgiving. Fixing mistakes means hacksaw replacements. You can see my pop bottles ready to go. The real challenge is seating the bottle caps in the frame with a solid / water-tight fit. Bottle caps are not made of the same plastic as PVC tubing, so finding an appropriate glue is tough ... and it has to be food grade. I settled on a combination of contact cement, silicon and hot glue. Really a dogs breakfast.

It's messy, but it works. Later, I'll drill holes in these caps for the water to flow through.

So, how to we ensure we only pump the correct amount of water into the bottles? Well this is a clever little trick. We sacrifice one of our bottle holes for an overflow pipe. The height of the pipe determines the maximum height of the water. When the water pumps to here, it will start to spill back into the container. That way, we don't have to have precise values on our timer. We can overshoot and still maintain a maximum level. 

It's very impressive to watch as you'll see in the video later.

Here's the return pip going back into the container.

Inside the container is the connection of the pump to the top-level frame. This is just a friction fitting.

The pump is a submersible fish-tank pump. It has to be powerful enough to lift about 5L of water 2 feet and hold it. It sits right in the nutrients.

And here's a video of the system in operation ... it's at 2x normal speed. The timer will do this about every 15 minutes.

So where are the plants?! Turns out there is fatal design flaw with this set up (two actually). I'll let you try and guess what it is in the comments. I have a plan for fixing it and will attempt it this summer. At that time I'll post an update and let you know how it went :)

(the original plans for the system can be found here)

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