I grew lettuce in water only 5 inches deep, and I didn't see any need for it to be deeper. I don't know how big chard gets, but broccoli and basil will be a real problem in a water culture (raft) system, because of size and plant support. Broccoli gets 4 feet tall and just as wide, and basil will get tall as well and likely need extra support to keep it from being top heavy (unless you keep it timed down).

Though I'm sure large plants can be done in a water culture system if the size and weight of the plant is carefully considered. I would use 2 inch thick Styrofoam if trying to grow things much taller than lettuce. Depending on how big your system is, and how much weight you have on the Styrofoam, even 1/2 or 3/4 inch Styrofoam will still float, but won't be thick enough to be durable enough to last long (unless you laminate it to a stronger waterproof material too).

hh,

Wow, I would have thought the lettuce would need more room. I had a couple heads in a four-gallon bucket and the roots were massive. Of course, one grew over three foot tall.

My basil never gets more than 2' tall, as I keep it topped. But I could easily rig a trellis with those Greenhouse tomato support things.

Another question, can I use multiple pieces in the same container? My thought is to build a simple 12' x 2' tray but trying to find any Styrofoam longer than 8' is almost impossible when it comes to shipping fees.

Mike

well, I guess it depends on the type of lettuce your growing. I was growing "butter king" and used 3 inch baskets. The plants were spaced about 8 inches apart, and only grew about 8 inches tall (until they eventually bolted). I also was using a 42 liter storage tote for the container. I wasn't using Styrofoam to support the plants. I cut holes in the lid of the storage tote and inserted the baskets in the holes. I just raised the water level to where it was just touching the bottom of the baskets. That wicked up moisture into the growing medium, and the roots grew down into the water.

But other varieties like iceberg, or romaine lettuce will be much taller. I have a picture of a commercial setup growing what looks like (about 1 1/2 foot tall) romaine growing in a water culture system, using what looks like 2 inch thick Styrofoam. But unfortunately I cant easily post pictures in this forum, and I don't know where I got the picture from. Though the picture doesn't show the water, guessing by the roots, I would say the water was probably something like a foot deep. But would probably be fine in as little as 8 inches of water.

The thing is with a setup like a commercial water culture setup, they usually recirculate the water. So they don't need to worry about the roots using up all the nutrients in a given volume of water. By recirculating it they also don't need to disturb the plants to change (or add to) the nutrient solution in order to maintain a balanced nutrient. That's what I think the biggest benefit in a deeper water level is (buffer water), so the nutrients don't become unbalanced too quickly. But also for water/air-bubble circulation.

So depending on if you use a reservoir and recirculate the water, and if you provide an even supply of sufficient air bubbles to the roots. As long as you can provide both, I don't think how deep the water level is really matters all that much. But If I had to come up with a rule of thumb (don't know if there is one for this), I would probably say I would go with a water depth of something like half the height of the full grown plant to provide good circulation for the roots.

Your really only limited by your imagination in how you design your system. Ya, they usually just sell 8x4 sheets of Styrofoam at Lowe's and Home Depot for home insulation (same size as the sheets of plywood and OSB board). And I don't see why you couldn't just cut the sheets into three 4x2 foot sections. That will give you more flexibility anyway. First it would be easier to take the plants out without needing to lift the whole thing at once (the weight of a lot of large plants may crack/break the Styrofoam when you lift it). Second, that makes it easier to have plants growing at different stages of growth, so you don't need to harvest, then replace the whole thing at once. The bigger the plants, the roots will still likely grow together (they were in the picture I mentioned).

But the drawback to smaller pieces of Styrofoam is stability for tall plants. Especially if the plant is just as tall as the Styrofoam is wide (2 foot tall plant, and 2 foot wide Styrofoam), makes the whole thing top heavy. Even a 12 foot long piece of Styrofoam 2 feet wide, with more than one row of 2 foot tall plants in the center will be top heavy, and likely tip over easily. Even one row in the center will likely tip over in a good breeze. In witch case 4x4 pieces of Styrofoam would be much more stable. But if you plan to trellis the plants that may not be an issue. Though I'm not sure how you would trellis something like large varieties of lettuce.

Raft systems are pretty common here in Thailand. Minimum depth depends on the size of the plant you want to grow and the spacing of the plants (to allow sufficient volume for the roots). As a rule of thumb, widely spaced plants can grow in shallower water, so long as the total root volume is the same.

As a practical matter, most systems I've seen here are using about 4" (10 cm) depth, because water is heavy and the support structure to elevate it would become more expensive the deeper you made the pond. That said, if you leave the system sitting on the ground, you can easily make the pond a foot deep or more. The deeper the water, the more stable the temperature, pH and EC, but the more total nutrients you will need to add, and the harder it will be to keep it all oxygenated. Especially here in the tropics, 02 depletion of the water is a major issue.

If you are not circulating the water, and not replenishing it either (like the simplified non-circulating systems developed in the University of Hawaii), then you need to consider that the total volume reserved for the roots of each lettuce plant (as an example) needs to be about 4000 cubic centimeters. This is because 4 liters is about the amount of water each plant will need during it's lifetime. At 8" spacing, the plant will have a 20 x 20 cm space to grow in, so the water depth will need to be 10 cm (4") to assure each plant get's it's 4 liters worth of nutrient solution. If the lifetime water requirement of the plant begins to approach 20 liters, then it might make more sense to use 5 gallon buckets to hold the plant and nutrient solution.

Obviously if you're circulating the water from a reservoir, or replenishing the solution, then you could make the water less deep, but then you'd lose most of the benefits of using DFT and might as well just use NFT.

Bigger plants need thicker foam to handle the weight, either way you are better off buying the expensive blue stuff than the cheap white stuff, if you're in the USA. The low density white stuff gets waterlogged after a few months. For lettuce, 1" is sufficient. I have grown chard on such a system, but I kept it trimmed, otherwise it would eventually have overwhelmed the styrofoam, the same was true for kale or collard greens. There are better ways to grow broccoli, imho, such as the bucket I mentioned earlier.

Most commercial floats are smaller than the 4 x 8 sheet you can buy, since handling sheets that big (and planting them out) would be very cumbersome. Some systems in universities actually have one small float per plant, but I know of no commercial operations doing that.

I wouldn't use 5 gallon buckets as a water culture system for broccoli unless you design it as a recirculating system. The broccoli will drink up a lot of water daily, causing as lot of fluctuation in nutrient concentrations.

Thaihydrofarmer
You said the deeper the water the harder it will be to keep it all oxygenated. I assume that's a typo. Although the water has the same O2 saturation point (shallow or deep), Of coarse I know that water pressure and atmospheric pressure will play a part in the saturation point, but I'm not really talking about water deeper than 2 feet. And atmospheric pressure will be the same anyway.

So even though the saturation point is the same, basically a larger volume of water equals a larger volume of O2 as well. So the oxygen levels will be more stable in larger volumes of water than smaller ones. Of coarse that assumes the plants are the same size in both examples. Because larger plants will use up much more oxygen from the water than small ones will. The larger the root system, the more oxygen is gobbled up by the plants.

I will have to test it out to extent, but I haven't seen the white Styrofoam ever get waterlogged. Also I have never seen commercial operations that used anything other than white rafts. Although the higher density Styrofoam would be much more durable, and probably can be made in white as well.

Before I would rule out non-circulating water cultures in 5 gallon buckets, I would need you to define "a lot". I have no idea what the lifetime water requirement of broccoli is, so can't say whether 5 gals is a sufficient volume or not. U of H students have apparently successfully used even larger static volumes of water (such as trash containers) to grow much bigger plants than broccoli.

Your analysis of oxygen saturation point in water ignores the gradient effects of the depth of the water and the distance from the roots. O2 levels at the surface of the water will be higher, O2 levels near roots will be lower, when the water is static (not moving).

"Still waters run deep"... in other words it's harder to keep larger volumes of water homogenously mixed... taking more effort in terms of design, larger pumps, etc. Not saying it can't be done, it certainly can. Some CEA operations sparge compressed oxygen into their dft streams, for example. Not your typical bedroom hydroponic setup, however.

I have waterlogged the cheap low density styrofoam from the local hardware store when I grew larger, heavier plants on it over the course of several months. But yes, high density white styrofoam is also available if you can find it. It's what I use here in Thailand, even for lettuce, since as you say it's much more durable. But the only high density foam I could find locally in the US was the "blue brand"...

The broccoli plants I grew were about 4 feet wide, as well as tall. I have no doubt they would have gotten bigger if I wasn't getting low on the Flora series nutrients, and just used miracle gro until they were to far gone. I can't see a plant that size being easy to lift off the top of the bucket to do nutrient changes, and/or other maintenance. Yes can could have a drain plug, but you would still need to take the plant out to clean the inside of the bucket.

I had 4 broccoli plants in 5 gallon buckets, but as a drip system with a 18 gallon reservoir. Between all 4 plants I would need to add 6-8 gallons of water each day back to the reservoir just to get the water level back to where it was. The system had no leaks, and it wasn't even hot yet because broccoli is a cold weather plant, so I grew them over winter. If I forgot to add water one day, the pump would be running dry the next day.

So each plant would be drinking 1 1/2 to 2 gallons of water each day. Assuming you had 5 gallons of water in the 5 gallon bucket, that would be at least a third of the water per day. You can add water through the top each day, but the water level fluctuating that much will cause the nutrient strength (EC) to fluctuate quite a bit constantly. I wasn't expecting them to drink that much either, or I would have gotten a larger reservoir.

Your analysis of oxygen saturation point in water ignores the gradient effects of the depth of the water and the distance from the roots.

I don't think so. First I'm only talking about water less than 2 feet deep, probably only 1 foot at most, so the gradient effects of the depth of the water should be minimal at best. Also I'm not talking about non moving water. Even if you don't recirculate it, using a high volume air pump (you can get for about $100) and evenly placed air stones will supply both circulating water, as well as replace oxygen used by the plants. That will also provide actual air to the roots. That's how a typical water culture system works, and what I'm talking about.

I don't think providing an even supply of sufficient air bubbles to the roots of a 12 foot long, by 2 foot wide container is a problem. But regardless of the water depth, if you don't have a way to sufficiently replace the oxygen used by the plants, your going to have a problem. Even if you do recirculate the water, I would still want a good air supply to the roots. Recirculating the water just adds the added benefits of being able to help oxygenate the water even more with falling water, as well as much easier nutrient maintenance.

Interesting reply.

Multiple air stones and 100 dollar air compressors are expensive, noisy and not very cost effective if all you're growing is broccoli and lettuce for home consumption, IMHO. Especially given that it can all be done without any pumps or compressors at all. So you kind of made my point, since I agree with what you said.

I looked up broccoli to try and find daily drip irrigation requirements. I could only find info for field grown broccoli, which came in at 112 gallons over 150 days per plant. That assumed the broccoli was planted on 2' centers and 3' between rows.

To compare, field grown lettuce was only 5 gallons over 50 days per plant (assuming 8" spacing and no empty space for walking).

That makes a broccoli plant about 22 times more demanding than a lettuce plant. Hydroponically that same lettuce plant uses only a gallon during it's lifetime, so I will guess you could grow a broccoli plant in a 25 gallon trash can without ever replenishing the water or nutes. That's my prediction, anyway.

As long as the space is ventilated, as the plant uses up the water the exposed roots that hang down should be able to take care of the plant's gas exchange requirements. No pumps or airstones needed, no need to check or adjust EC or pH, if the initial mix is properly matched to the needs of that plant. Just fire and forget.

Optimal? No. But it does work surprisingly well. Sometimes we make things far more complicated than they really need to be.

I'll make it a bit more complicated. I use Tomato-Tone dissolved in water as a nuit. Great, but if not aerated, tends to stink after a few days. But I have the air pump, the tubing, everything I need.

Adding nuit solution is a one minute exercise: turn on the pump. Checking pH and EC/PPM levels also takes maybe a minute or so. Time I don't mind spending. Yes, I know I can stick a plant in water and in time get something from it. But too much has been studied and written about better ways, methods that produce more, uh, produce, to ignore. I'm not planning on doing this so I can have rabbit food for a meal - I want to sell the stuff. The quicker I can get the biggest and best heads to market, the better for me.

But I appreciate your all's discussion!

Mike

Umm that's a whole different discussion. I know some lettuce farms around here with separate reservoirs for each of their 6 meter x 2 meter raft tables (a typical size). That 1 or 2 minutes times 50 or 150 tables adds up! They all started with just one table also, but separate reservoirs don't scale well. Their one or two minutes have become hours.

Others run to a central reservoir, but risk major disease breakouts as a consequence. No easy answers. I look at all technology questions from a cost benefit perspective. Does that improved yield come with greater risk? Does the extra investment in a more complex setup pay for itself? Or would it be better to invest in two simpler systems than one more complex one?

Every situation is different, I am still investigating those same issues here.

But going back to answer your original question, I'd say it is 2 or 3 mm. deep. But then it is really NFT, even if the plants are sitting in foam rafts. I saw a YouTube video just the other day where someone had done just that.

Air stones run about $2-$2.50 here, so I don't consider that much of an expense. Even spacing them every foot in a 12 foot long container. And I wasn't thinking of an air compressor, I was thinking of a high volume aquarium air pump such as these.

High-Pressure Aquarium Air Pump
Super Luft Pump

They don't put out anywhere near the noise a compressor does, and come in all sizes and prices. Especially the second one with 2.3 cubic feet per minute output. For under $60, I don't think that's expensive. Especially considering the cheapest water pumps I have cost $30, the next one up was $45. Sure things can always be done cheaper, but cheaper isn't always better when you want a quality product. That's why I would never consider growing in stagnant water.

I have a 950 GPH air pump with a 12-outlet diverter and rather than using air stones, I use a 1/4" soaker hose. I can run it the length of the bed.

Once I start building it, I may go in 6-foot sections, as I would like to start new plants every couple of weeks. The nuit concentration and/or water levels would need to be a bit different.

Mike

Have you used the soaked hose for an air stone replacement before? I know the flexible air stones clog easily, and can only imagine the soaker hose is a similar material. If it doesn't clog, I like the idea myself. I also wanted to try it for the drip rings in future drip systems, but I'm concerned about if the mineral salts/elements will clog the soaker hose as well.

HH,

In several grows, some for months at a time. Sends out small bubbles and if it clogs, I have not noticed it. I switched to it because I had some of those rigid air stones clog and almost lost plants. The only negative I have found is that it tends to float, so I place small weights (rocks, pieces of concrete block) on them.

Mike

By now, you may have already figured out your dilemma with styrofoam thickness and spacing. I'm starting my first raft on my kitchen counter now, but have used the bubbler method for my fruiting crop before with success. After much research, the general rule is that you can space leafy lettuce (like buttercrunch) a mere 3" apart in 2" cups (you'll be harvesting these as they grow to take advantage of tender young leaves, but they'll have plenty of room anyway). If you grow head lettuce, they need their own larger pot and need a whopping 12" space between pots, making them a poor choice for my 2x4 countertop garden. I'm also growing oregano in the same unit, but will be topping often and using the herbs as they grow. The big experiment for me is that I'm using a 5" pot with soiless mix of peat and perlite - non hydro, but using same nutrients - utilizing the same light source as my hydro lettuce/oregano raft to grow basil and green onions. In my estimation, they will all use the same lighting schedule, should never need HID because none should bud/bloom as long as I keep my onions topped. I'm hoping for a countertop covered in green, but we'll see. May need another light, but fluorescents are cool, and cheap. BTW, I use an aquarium pump with two outlets ($20 at Walmart) and run two airstones (long, narrow type) in my hydro unit and it's working great with lots of bubbles. The containers hold about 12 gallons, but use about 10 and have 6 healthy plants going strong. I plan to use the same type air pump for my lettuc raft and probably one stone, as my water depth won't exceed 6 inched or so.

I used the air pumps from Walmart also on a two smaller raft floats (2'x2' and 1.5'x3'). I am preparing for a bigger system this fall and ordered a lot larger air pump. Mostly growing Boc Choy, kale and lettuce. Will just change by water solution out every 2 weeks.
I will be using the blue Styrofoam from Lowe's as my float, thinking about 6'x3' as my final size.