When someone describes an experiment, it should be done in sufficient detail so that others can duplicate the results.

"Control, growing in 4" pots of soil"

"Soil" is too vague. It can be anything from dirt from the ground to a mixture of peat moss and rice hulls. Exactly what was your "soil?"

"no additional nutrients added"

Initially, how much, and exactly what nutrients were added to the rock wool and the "soil." I point out that it would be a mistake to not add the same nutrients to the "soil."

How long did it take the seeds to germinate in the rock wool and controls?

It would have been easier and more educational to use the same fertilizer for both soil and rock wool because all of the different results could have been caused by the difference in fertilizers.

One week update:

I decided to let the grow continue rather than harvesting the whole plants. So last week I heavily harvested both the DWC and Kratky lettuce. I just left a few small leaves in the center of each plant. I changed out the DWC nutrients, and refilled the Kratky container since it had only about 1/2" of nutrients left in the bottom after the month of growth! Even though I have read that you should only raise the level a little to keep the roots that were in the air from drowning I decided to just go for it and raise it to where only about 3/4" of the root mass was above the water. The whole point of the Kratky method for me was to minimize maintenance so thought I should give it a try.

Well, plants didn't seem to mind. Had another full harvest today with the Kratky plants growing quite a bit more than the DWC. Hard to believe the lettuce could grow this fast in the Hydro setups. The control growing in soil is almost ready for a harvest but the leaves are still very small. The Kratky plants look very healthy so going for another harvest next week (family is getting a little tired of salads every night haha!), The DWC plants seem to have the remaining leaves stunted a bit and curling on the ends... maybe I damaged the roots when changing the nutrients. The roots are now a bit more yellow, compared to the very white Kratky roots.

I am going to go ahead and see how long I can keep the Kratky plants producing....

Apparently, there is more than one brand of lettuce formula 8-15-36. The HydoGardens brand,

https://hydro-gardens.com/product/lettuce-formula-2gal-pail-8-15-36-2/

instructs users to add calcium nitrate and magnesium sulfate. Although I have never grown lettuce, I use HydroGardens Chem-Gro 10-8-22 for a lot for other things in soilless mix. Also, I have had success with Peters Excel 15-5-15 Cal Mag

http://www.growersupply.com/peex15calmag.html

in ground soil, and, will probably buy more now that my old supply is gone. Peters Excel 15-5-15 is unusual in that all of the P is in the form of urea phosphate and it is very acid.

Yeah, I got my 8-15-36 from Amazon link below:

http://www.amazon.com/gp/product/B00VF3VT4C?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I just wanted to try a pound before committing to the larger sizes with the Chem-Gro which Kratky recommended too. Pretty sure it is the same stuff based on ingredients though, and I just put an order in at HydroGardens for the tomato and the pepper in 5lb sizes since I am switching everything over to hydroponics now. Could probably have just gotten along fine with one formula for all three but what the heck.

The advantage of adding the calcium nitrate and magnesium sulfate yourself (besides allowing altering the nitrogen level per plant stage) seems to be in being able to mix up batches of concentrated liquid in advance. I understand the all-in-one formulas can't be concentrated. I followed Kratky's advice in just making two concentrated solutions from the powders. I used 1 liter soda bottles. One is the 8-15-36 mixed with magnesium sulfate. The other is just the calcium nitrate. So now I just pour in a tablespoon of each for each gallon in the tank. Easier than dissolving the powder each time I add nutrients.

Starting the tomatoes and peppers soon. I just found some cool little 1/4" tubing float valves for each of my tubs so am going to try Kratky method combined with a gravity fed tank system since they will need more nutrients over their life than the tubs can hold. Nutrient level will be maintained without pumps and no air stones required either! In theory "zero effort" growing but we will see!

Stu Zone, $17 per pound is crazy. Most typically, chemical fertilizers in 25 lb. bags costs less than $2 per pound. If you have a garden, you can also use it outdoors, in which case, 25 lbs. is not unreasonable.

I recommend that you perform a controlled experiment. Under otherwise identical conditions, grow two groups of lettuce but only one with added reagent grade urea 1 g./gal.. It is important not to use more! You can buy it here:

http://www.ebay.com/itm/Urea-3oz-Reagent-Grade-99-9-Pure-Sturdy-Bottle-SHIPS-SAME-DAY-/191794776298?hash=item2ca7dc08ea:g:CY4AAOSwg3FUqbum

Also, you may as well also buy thiourea from the same seller.

If you Google,

thiourea "plant growth"

, you will get 58,900 results, many of which are very interesting. Maybe, thiourea can be used as the sole source of S in hydroponics. I expect that, unlike soluble sulfates, it won't form insoluble precipitates with calcium. I have no experience with thiourea but I am going to experiment with it in the spring.

Third weekly harvest and both the Kratky and DWC still doing well. They drink a lot of nutrients at this size, I am pretty much refilling the Kratky tub each week. The DWC tub I have resorted to keeping topped off with nutrient formula now since just adding water diluted the nutrients too much. The DWC harvest was a bit more than the Kratky this time, and the leaves slightly longer/wider.I had to lower my shelves again to keep them from growing into the LED's

These results have made me rethink my planting schedule- I was planning on growing 4 weeks then harvest entire plant- I didn't know I would be another 4 weeks+ of continual harvesting! Now what to do with those rockwool seedlings waiting for their spots to be available "I am sorry, there is another plane at our jetway and we will have to wait out here on the tarmac until it clears"

Stu, looks great!

I have been growing Kratky lettuce outside for a few seasons and recently started thinking about starting some type of indoor Kratky/LED grow box to get us through the cold months.

Can you elaborate on the the "6500K Cree LED's" (link to what to buy) and the rest of your indoor setup? I would love to see a couple pictures. I know nothing about indoor lighting....

Thanks! Yes, well my experience can be summed up by the fact that I just redesigned my outdoor garden for this year without space for lettuce! Made more room for the bigger things that are harder to grow indoors. I never had any of my outdoor lettuce grow like this. Lighting doesn't have to be LED, people are using florescent fixtures with great results. Lettuce seems to be very forgiving, just cool white bulbs. But if you want to work with LED's, then this is what I put in:

http://www.ebay.com/itm/10pcs-lot-Cree-XT-E-5W-Cool-White-Led-on-20mm-Star-/311516165243?hash=item4887cf747b

I have 40 of them for a 2x4' grow area. You can put the plants within an inch or two of these since they run pretty cool.
Not exactly plug n
play though, you have to learn a bit about heat sinks (I glued them to
1/8" sheet of aluminum), and power supplies but once you figure it out
it is as simple as wiring a power supply to the LED's - no other
circuitry required. Here is a shot of my setup for lettuce- I drop the shelves lower as the plants get bigger.

Thanks for the info!

If you want to buy LED lights, I have had good luck with Cidly Aquabar lights, they are passively cooled and will create a custom spectrum, with whatever you want for no additional charge. They have 2', 3' and 4' lights for $30, 40 and 50 respectively. They work great for aquariums and growing plants. Worth checking out if you are in the market. If you are growing plants that require high intensity, these might not be the best, for for leafy greens, they would be more than enough.

Nice looking lettuce! I need to research this kratky method, do you have a website link were you got your info?

Thanks! You can read about it from the man himself here, I just followed this to the letter nutrient wise.

http://www.ctahr.hawaii.edu/oc/freepubs/pdf/vc-1.pdf

Thanks for the link, looks interesting! Another project to try....

If you get into it, I am happy to share details of what I do. Pretty straightforward though. I am growing 5 heads of lettuce in 2" net cups per each 3 gallon tote. Pretty much just set it up and leave it until ready to harvest. No maintenance!

Final Harvest Report:

So on the 5th week of harvesting I decided to pull the entire plants. I had already started the next generation to replace these and they were outgrowing their little rockwool cubes. Also, the leaf size had begin to get slightly smaller on the Romaine, and the ends had started to brown. Looking at the roots, they had changed from their pristine white color to a light brown so alas it was probably only good for another harvest or so anyway. The Kale would have kept on going another couple weeks from the look of it. Now I have Red Fire, Butter Crunch, Arugula, Basil and Cilantro growing in their place. Also experimenting with a larger tub with 4 tomato plants in Kratky.

I have set everything up with little float valves in each tub that are fed from a large tank through gravity. Once the nutrient level drops to a set point in the tub the valve will maintain it at that level. I was manually adding a lot of nutrient with the lettuce since I was harvesting for so long. I think the wide swing in nutrient levels was not good for the roots. It is also essential to have more nutrients for the tomatoes since they will be growing much longer.

This will be my last update on the thread unless anyone has any interest in seeing what happens with the next generation.

Tomatoes- 10 gallon tub:

Arugula and Red Fire- 3 gallon tub:

Butter Crunch, Cilantro and Basil- 3 gallon tub:

Can get 50lbs of Jacks hydro ferts for less than 150 shipped. Seems like a good deal but not sure I need 50lbs of fertilizer! Its way more expensive for smaller quantities tho...

http://www.jrpeters.com/personas/hydroponics/shop-now.html

Stu, love this thread and your info and do hope you continue to update us. I think you've convinced me to build my own led setup in my similarly sized space for my impending Kratky lettuce build. Could you please give me info on the power supply/driver you are using to run those Cree LED's? Also, where did you get the aluminum sheet if it was purchased online? Thank you so much, and thanks for the great informative posts!

Thanks pixiedust!

One of these will power 8 of the LED's I listed above- I bought 5 of them for my 2x4' panel that has 40 (4x10) of the LED's:

http://www.dx.com/p/waterproof-ip65-50w-10-series-5-parallel-integrated-constant-current-power-led-driver-100-240v-398675#.VuQOT0d0ac0

For the aluminum sheet, you can get it most anywhere, just make sure it is at least 1/8" thick to dissipate the heat. Ebay has them here but I didn't buy from this seller:

http://www.ebay.com/itm/1-8-125-Aluminum-Sheet-Plate-24-x-48-6061-/271025780988?hash=item3f1a6538fc

I found that a small fan blowing a gentle breeze across the top of the panel is all that is needed to keep it cool. I ended up gluing some little temperature switches to the panel (because i like to tinker) so the fans only come on when needed but this is not necessary. I did notice the fans didn't run at all over the winter down in my basement.

You will need some thermal glue to adhere the stars to the aluminum sheet:

http://www.ebay.com/itm/Hot-Thermal-Compounds-Conductive-Heatsink-Adhesive-Industrial-Glue-For-PC-GPU-IC-/351461284609?hash=item51d4b99b01

And then just wire the 8 stars in series to each power supply. Note that this will drive the Cree XT-E's at their full rated power which is not the most efficient thing to do, I have since started designing my newer lights to run more optimally.

One other thing, I built my unit based on the 2x4' home depot shelving units. Was pretty handy to already have the frame and shelves. I just dropped in the aluminum panels instead of shelves where I wanted them. Since mine was going in the unheated basement I boxed it all in with insulating foam covered with silver mylar.

Good luck with your lettuce!

Thank you so much for all of the great information! :)

Yesterday, the TV show, 1st Look, had a feature on Green Sense Farms. They hydroponically grow greens on ten tier racks using red and blue Philips LED lights. Look at this picture:

http://i.kinja-img.com/gawker-media/image/upload/s--kPfYVWnN--/c_scale,fl_progressive,q_80,w_800/reoo7aw27nnh2zts6gi7.jpg

and, they have a lot of racks. If I had to guess, I would guess that they are consuming about a million watts of electric power. Here is their web site:

http://www.greensensefarms.com/

I just now asked them what is their total grow area and power consumption. I bet they keep it a secret.

I really need help!!! And quick too, as I need to get started.

What lights did you use? I can't afford those expensive full spectrum lights. I want to also grow peppers and tomatoes. Read that I need blue and red high out put lights. Crazy expensive though.

I am disabled, can't really do gardening. (Weeding, pest control daily, soil enriching, etc) Can't grow outside. The kraky method is perfect! But the lights!!!!

I have a spare room I can use to make into an indoor green house. Was so excited. But now I'm discouraged. I also read I needed air stones. Your post is encouraging, as that would add to the electric bill. Nice to know I don't need them. Can you help me with a solution for the lights. Hyper tough had LED 5000 lumen. I thought that might work for greens. But not sure now..What about the other plants like tomatoes, cucumber, etc.

Thanks so much. And thank you for posting your experiment. So helpful.