[GpsFrontier]

Hello Paul Perkins,

1. Do you have any suggestion as to how high the water level should be inside the totes? Up to the top? Just above the bottom of the netpot? Does it matter so much as long as the roots are wet and the water is aerated?

The water level should be high enough so the growing medium is moist, but not saturated. So the type of growing medium, and how much water it holds is a factor. In the system I built, I was using coco chips as a growing medium. I had the water level high enough that the bottom 1/4 to 1/2 inch of the baskets were submerged in the nutrient solution. But it's also common to have the water level about 1/4 to 1/2 inch below the baskets, and the constant spritzing of all the bubbles on the surface of the water making the growing medium moist. That may be a better option with rockwool as a growing medium because if you submerge the rockwool at all, it will likely wick up to much, and thus become too saturated. The water level in this system is easily adjustable (just add water, or take some out).

Water level is also the reason the containers/storage tote I used were only about 5-6 inches tall. With the baskets in the lids, the water level in the storage totes only needed to be about 4 inches high. Even so, it still took about 6 gallons of nutrient solution to raise the water level to where I wanted it. With 8 plants in the system, and small plants like lettuce requiring a minimum of 1/2 gallon per plant of nutrient solution. 6 gallons of nutrient solution was plenty of water. If it were deeper, it would have just took more nutrient solution to fill.

2. Re: the seedling stage. After germination, I read that you suggest a storage tote with more holes spaced more densely together for growth prior to moving into the main system. Other than the closer spacing of the holes, do you do anything different in the "seedling" stage than what you do in the "main" stage? For example, I've also read that the nute solution for seedlings should be 1/2 strength versus growth stage. True? Do you give your seedlings more sun/less sun? Lower waterline of the nute solution to just wick the rockwool versus immersion, etc.?

True the only thing different in how the seedling system is built verses the main system is the plant spacing. And yes, the nutrient requirements for seedlings are lower. So I would use 1/4 to 1/2 nutrient strength for the seedlings. As for light, if your using artificial light, I would keep the light level the same as for the maturing plants. Otherwise they may become elongated. But if your using natural sunlight and the sunlight is too strong, it could damage seedlings. So depending on your location and the weather conditions, partial shading may well be more favorable than direct all day sun. Also if your system is in direct sunlight you may need to take precautions, or make alterations to keep the nutrient solution temperatures from getting to high (68-75F is optimal). In which case a larger volume of water would be beneficial. Smaller volumes of water heat up faster than larger ones.

3. In your pictures, I see you built a shade over your lettuce. I live in Central Florida where our afternoon sun is nearly comparable to the intensity in AZ. Did you find that without shade your lettuce couldn't handle the intensity?

I built the system in early spring (last year), and didn't use shade cloth most of the time. But once the daily temperatures started reaching upper 80'sF, I added the shade cloth cover for a couple of reasons. One, it's true that lettuce is a low light tolerant plant, and thus shading it would help protect it from the all day direct sunlight (and increasing intensity). But also, by shading it I was hoping to help keep the temperatures at the plants a few degrees lower. Prolonging the plants season before they bolted because of the warm temperatures. Also hoping to help keep the container from being subject to direct sunlight and heating up the nutrient solution and roots inside. You cant see it in the pictures, but there are actually 2 containers (and just one lid). One storage tote inside the other one, with a layer of insulation between them trying to protect the inside container from the outside heat. Not the best option, but all I had to work with, and worked fairly well.

4. What propagation medium would you suggest for lettuce?

I would want something easy to fill the propagation trays with like coco fiber (my particular choice), Perlite, or Vermiculite. The size holes in the baskets/cups you use will dictate what you use can effectively use in the main system (you don't want it falling through the openings). Here Again I would prefer coco fiber. But at the same time use small plastic cups, rather than baskets. I can get 5-8 oz plastic cups at the store and only cost about one or two dollars for 50 to 100 of them. Then use a small hand soldering iron to make holes in the bottom. That way I can control the size of the holes, and I wouldn't need to clean and sanitize them before reuse (because their cheep enough to be disposable). I can easily make holes in well over 100 plastic cups in about 30 minutes or so while sitting and watching TV at the same time.

But there are a couple of notes here. First, colored plastic cups would be best for protecting the roots from light. But at the same time the system should be light proof anyway, so colored plastic isn't necessary while the cups are in the system. Second, baskets have slats all around them. Allowing it possible for the bubbles bursting on the surface of the water to wet the growing medium. So if using plastic cups and making holes in them, you wont get the same effect of water getting to the growing medium by spritzing. The cups would need be a 1/4 inch or so submerged to wick up through the coco fiber effectively. so it really depends on how many plants are planed, labor, and personal preference.

5. Finally, for a custom DWC lettuce growing setup, what do you think about using a Firestone PondGard EPDM "Fish Safe" liner inside a wood frame with blue foam polystyrene as a float surface? Any suggestions on how deep a DWC system should be? Is EPDM safe? Any better materials to use?

What you describe is almost exactly what I have planed to build, including the high density blue board Styrofoam. Except mine will be a flood and drain, rather than a water culture system. I haven't posted these pictures before, I created them for the business plan I'm working on. Their not 100% complete or to scale, but give a good idea of what I have in mind. I will be using OSB board for the base, and 2x4's for the side. Even though the pond liners would work great, I'll be using 6ml black plastic sheeting because it's less expensive. But I will also be using Elastomeric Roof Coating to bond it to the wood rather than contact cement. The roof coating is much thicker, waterproof, and easier to work with on rolled plastic. It just takes a good 24 hours to cure. Also I'll be growing small herb plants (up to 10 inches tall), and the water level will be between 2 and 3 inches when flooded. So the water depth isn't really important as long as the growing medium gets saturated when flooded.

How deep should a water culture system be? Well first DWC implies "deep water" (Deep Water Culture), and is generally more than 10 inches deep, but that's the only difference. As for how deep should the water be, how big the plant being grown gets is important. Smaller plants have smaller root systems, thus shallower water is workable. For most small varieties of lettuce I would probably go with 4 to 6 inches of water. But for large varieties like romaine lettuce, I would probably want at least 10 to 12 inches. I haven't grown romaine, so I don't know how large the plant gets (only how big the heads they sell at the market are). Either way for a large custom build, I would also use a water pump, and secondary reservoir to circulate the water thorough the system better.

P.S. jamromhem
Your post hadn't posted yet when I started my post, so I didn't see it until I was done. Also I think I'll look for some of that polyester batting you speak of. Is it cheap?