Lettuce production thoughts.

[sameerraut]

Hi! I am a Botany student and am too interested in DWC Hydroponics. I really like your design. I will really appreciate, if could solve few of my queries.:
What should be the time frame for changing the water in the reservoir for DWC?
How should be the specific design for the reuse of the water (considering your above design)?
What would be best option as per you, I mean to keep the water flowing or to keep it still & changing it later. and in both cases what would be time frame to change the water.
Are there any chances of getting the water contaminated with the Mosquitoes in DWC, if yes, How could we prevent it?
I planning to cultivate 1000 lettuce a week using DWC, so it will be helpful if you could provide me a rough idea about the space that will require and a rough diagram/design about showing how the flow of water will work to preserve as much as water.

[jamromhem]

I have a few thoughts on your questions. The mosquitos could be controled in a few ways.. if using a constant water flow it would reduce the likelyhood that they would even consider it as a place to procreate. Also with regular water changes (every couple weeks in most hydroponic systems) They will be less likely to take hold.

Another option is if you use bleach to get the chlorine levels similar to that of a pool. (I have been germinating my seeds in a 10ppm+ bleach solution and they don't mind). I use a higher concentration for germinating because it tends to be stagnant water and more likely to become infested with various things than moving water.

If using bleach do not use H2O2 you will make salt water and nagate the purpose of adding either because they react with eachother.

Water conservation is a tricky question, because the amount of water in the res and if you use it as dump water or if you refine the water after use decides the conservation of it. Typically hydroponics is more water efficient than normal growing. The water is held away from the open air so it condences back into the system rather than floating off into the flow of air. Also the water change cycles will depend on your ability to maintain the quality of the nutrients, as well as the size of the res. I think it was mentioned before lettuce typically uses 1/2 gal of nutrients a week (might be wrong on that one it is somewhere in the forums) So if you have a larger res and can maintain it's quality you can go longer before changes. If you use a smaller res you have to change more often because the plants use up the nutrients and you would be starving them of what they need.

On a side note about the polyester medium. I have been playing with a few varieties of it to see about the quilities as a medium.. The quilt batting is my favorite so far. The poly-fil for stuffed animals and pillows tends to be a thicker fiber and seems to wick very little. If using the poly-fil I would suggest a top drop from what I have seen so far... The quilt batting wicks nicely in comparison. I have some oregano and cilantro on a piece of batting and the oregano is starting to germinate with just the moisture that is wicking up from the edges of the batting that I have in the humidity dome. Not to mention the large surface area provided from the poly (the small pockets of air in the batting) lets the dew form all through it. I will make a thread with my findings on what I have tested so far and try to keep it updated as I find things.

[GpsFrontier]

What should be the time frame for changing the water in the reservoir for DWC?

This will vary. Some of the biggest factors include water volume, plant size, plant to water ratio, water temp, if it's stagnant or circulating water. Especially overall size of the operation, and the water volume. As an example, generally really large operations never actually fully change the water/nutrient solution at all. They might change part of it, but generally they use a large volume of water to plant ratio (so nutrient depletion is slow). They also monitor individual nutrient levels by lab testing samples of the plant tissue. That tells them what mineral elements are lacking, and they can then compensate for it by adding just the specific elements that are lacking (not a nutrient mix, the individual elements). Of coarse experience also plays a part also, because over time they simply learn the pattern of what nutrients are used faster than others from the regular tissue testing.

How should be the specific design for the reuse of the water (considering your above design)?

I'm not really sure what your asking here? If your asking what my plan is for changing the nutrient solution in the system I plan (not the original poster who plans on using a water culture system), I expect to be changing the reservoir between 3-4 week intervals. But I may not always change the entire reservoir either. I may wind up changing 50% of it every other time (or something similar). Especially for the seedlings. I'll be growing small herb plants, and small plants that are not much older than seedlings themselves just don't uptake nutrients very fast. So I expect to be able to go 4 weeks before seeing signs of any deficiency.

What would be best option as per you, I mean to keep the water flowing or to keep it still & changing it later. and in both cases what would be time frame to change the water.

Again I'm not sure I understand the question here. But if your asking whether it is better for the water to circulate or be stagnate. It's always better for the water to be moving, even in a water culture system. The roots can only uptake the nutrients in the water around them. Once they do, there's less for them to access. So circulating the water keeps the nutrient solution evenly mixed.

Are there any chances of getting the water contaminated with the Mosquitoes in DWC, if yes, How could we prevent it?

Absolutely, unless you design the system to be air tight. But that wont be very efficient because the the dissolved oxygen levels in the water will drop, and wont be able to be replenished. If you keep mosquitoes out of the greenhouse area in the first place there is less of them to breed in the first place. You can use bug zappers, mosquito netting, sticky traps etc.. But as jamromhem mentioned mosquitoes don't like to breed in moving water, so simply keep the water moving. Easily done with bubbling water from a air pump, and/or circulate it with a water pump.

I planning to cultivate 1000 lettuce a week using DWC, so it will be helpful if you could provide me a rough idea about the space that will require and a rough diagram/design about showing how the flow of water will work to preserve as much as water.

Well first I would need to know a lot more details to be able to design the best hydroponic system for you, but if you are concerned about using large water volumes you may want to consider a NFT system. Unless you plan to do plant tissue testing and nutrient monitoring. But if you want to harvest 1000 heads of lettuce weekly, you'll need to be growing at least 6000 to 8000 total plants at any given time. With another 1000 germinating. What space do you have to work with? From there you'll need to figure out your plant spacing to see if you have space for it all (plant size is a factor their). As well as the hydroponic system, and nutrient reservoirs. Can you afford to build the greenhouse you'll need?

How do you plan on doing climate control in the greenhouse? Will you need artificial lighting. What type of lettuce do you plan to grow? That makes a difference in the hydroponic system design requirements. Small lettuce heads can be grown much differently than larger heads. Also What do you plan to do for lighting (artificial or natural). As well as your location and plant size makes a big difference on the best system design and setup. Including weather you will be able to take advantage of vertical space and stack a system, and/or need to stagger the levels for even lighting or not. It's just hard to give specific advice without knowing any of the details.

But if you are wanting to get into a commercial operation for growing hydroponic lettuce. I would strongly recommend getting the book Hydroponic Lettuce Production, it's written by Dr. Lynette Morgan. Also here's a useful link that discuses different aspects of lettuce production: Cornell University Lettuce Handbook

I also have a couple of PDF's you can print out as well
Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce
Commercial Hydroponic High Value Specialty Crop Production at Chena Hot Springs Resort.

[sameerraut]

Thank you for your help. The suggestions and the links you provided are very useful for my project.

[jamromhem]

I was thinking about making something like this for my lettuce, to replace my current system while I am working out the bugs. I will perhaps use the current system later for some other ideas.. I am sure I can come up with some ideas for it. I was thinking about perhaps using a roofing cement similar to
Roof cement for $10
to use as the cement to put the plastic down.

I have a feeling this will be more than enough to build 2 of these systems since I am only wanting a thin layer of the cement to protect the plastic from the splinters of the wood.

On a side note.. I am considering making a small soil planter for a few lettuce to use as a comparison of growth to determine if hydroponics are growing resonably. This is more of a self note of progress/setbacks since I have no past experience with the plants I am currently growing.

[GpsFrontier]

Interesting, My first thought was it looks like roofing tar, and roofing tar needs to be heated before it can be applied. But it clearly says "Cold Process," so that has me wanting to look into it as well, especially if it's cheaper than the elastomeric Roof Coating.

[jamromhem]

That is my main reasoning to want to try it as well.. I have tried to work with cold tar before and it is far from fun lol.. My brother had a tree rip down the power line to his house last winter and at the probably 20 ish degrees it was outside patching the roof with tar was not very fun... A LOT worse than normal.

but a 20 dollar difference in a gallon is worth an attempt.. We will see which of us check it out first. If HD still has it next week I will be getting some for making my new lettuce system.