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Thoughts on my setup?


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Old 09-15-2014, 10:39 AM
ematt ematt is offline
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Default Thoughts on my setup?

Hi all,

This is my first venture into hydroponics, and also my first post! Great to be here right now.

I've just started experimenting with hydroponics, growing a few lettuce seedlings. They're seeded in 1 inch rockwool cubes.

I had some early problems with white gooey stuff on the bottom of the rockwell cubes (I never worked out whether it was fungus or algae). I noticed at this time that the nutrient solution was rather warm, and so I've designed my system with a cooling mechanism, and have had no subsequent problems in this area.

I have had some other problems though, and I'd be grateful for any thoughts. Before proceeding though, a little more about my setup. I do like a little animation, so I made one for you so you can see exactly what I've done. You can view it here: www.youtube.com/v/t_94rkgyKnU

My lettuces are growing, but I'm suspicious they're not doing as well as they could be. Here's a photo of what they look like now, at 22 days since sowing (the red lines show you the size of the tin foil covered square base, to give you a feel for scale):



They seem to be a bit "wilty", and they each only have one tiny, thin root, about 2-3cm long, emerging from the bottom of the rockwool cube. I had imagined that by now they'd all have a nice bunch of roots emerging. I can see a few roots protruding from the edges and the top of the rockwool cube. So it seems there's definitely root growth happening, just not outside their tiny rockwool cube. My guess is that I'm not providing a humid enough environment below the rockwool cube. Maybe the draining of the nutrient chamber sucks in dry air from the room, which limits root growth. Any thoughts?

I guess a better system might be to keep the water cool with a thermal syphon instead of gravity syphon, as they do with passive solat hot water systems. My main concern is that I'd not be providing enough mixing to keep oxygen levels high enough. Does anyone know where I can read any guidance on how much mixing is enough mixing? E.g. recommended flow rates from certain heights for a certain volume of nutrient solution? I imagine it depends a lot on your system, but it would be great to see examples of what isn't enough, and what is enough!

Another problem might be lighting. I'm in Greenland, so am planning ahead of the dark winter coming and am using a metal halide light. I am using a 150W bulb, and a V-reflector held at a height of 40 cm above the base of the plant. I have a lux level meter that says the illuminance on the plants is about 15,000 -> 20,000 lux, and I keep this on for 16 hours a day. I know illuminance in lux is not a suitable indicator to understand how much usable light the plants are getting, but the lux meter is all I've got I'm afraid! Does it sound about right? I could lower the lights more, but that seems a bit intense.

Many thanks in advance for any thoughts/advice you might have, and of course, happy to answer any questions!

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Old 09-18-2014, 03:12 PM
Stan Stan is offline
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Is the rockwool constantly soaked in water? If yes first thing I would do is take the plants out of the rockwool and put them in hydroton. Rockwool holds lots of water and could be doing damage to the roots of the plants. Rockwool is great for starting with seeds but not good if it's constantly wet with growing plants.
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Old 09-18-2014, 04:08 PM
ematt ematt is offline
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Hi Stan, thank you so much for your reply!

Please could you point me to some online (or otherwise) literature that describes the problems of soaking rockwool seedlings in a bit more depth?

I have been reading a lot of Dr. Howard Resh's work (author of the convincingly titled "Hydroponic Food Production - a Definitive Guidebook", and his website), and he talks a lot about these floating raft systems, which are used for commercial production of lettuce. In these systems the lettuces are sown in rockwool, and then put into water rafts where they are constantly soaked in nutrient solution. Similarly NFT systems also soak the plants in nutrient solution, right? I suppose, in essence though, if you can get the roots to emerge out from the bottom of the rockwool cubes, then you no longer need to soak the cubes at all, only the roots! My problem is that I can't seem to persuade the roots to emerge at all...
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Old 09-18-2014, 04:33 PM
Stan Stan is offline
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Go to this link and you can read how saturated rockwool can damage the plants you want to grow.
Growing Mediums for Hydroponic Systems
As I said before rockwool is great to start plants from seeds but once the roots start popping out from the rockwool I usually transplant them into hydroton.
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Old 09-18-2014, 09:52 PM
GpsFrontier GpsFrontier is offline
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Hello ematt,
Like Stan mentioned, it's fine to start the lettuce seedlings (or anything) in rockwool cubes, but the idea behind the floating raft (water culture system) system your freferig to is to keep the roots continuous submerged. Not the growing media/rockwool cubes, just the roots hanging down out of them. Rockwool cubes absorb too much water and easily becomes saturated, thus can easily suffocate the roots. The roots hanging down in the water are kept from suffocating because of all the air bubbles rising and circulating the water. With some growing medias it's fine to have it touching the water because it wont absorb so much water, but rockwool sucks it up like a sponge. Generally the spray from splashing bubbles 1/2 to 1 inch below the cubes is plenty to keep rockwool cubes moist without saturating it. The air bubbles don't penetrate the rockwool cubes, so any roots inside it can suffocate. That can also lead to root rot. Another issue you can easily wind up with saturated rockwool cubes is stem rot. Stem rot occurs when the stem of the plant is continuously subjected to moisture.

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Last edited by GpsFrontier; 09-18-2014 at 09:58 PM.
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