Due to the lack of soil compaction, hydroponically grown plants are capable of growing massive root structures. I would recommend 4-6" net pots for the toms & peps. I haven't grown lettuce so I can't say for sure but I think the lettuce can go a bit smaller, maybe 3-5". I would highly recommend some form of sub aeration, as the roots are sure to grow through the pots and into the solution below and the submerged parts need O2. Any roots above the surface of the solution (in the vermiculite) should not be allowed to dry out but should always be kept moist. Thats the trick, Always wet but never drowning. Grizzman Has some awesome Pix of root structures somewhere on this site but I can't remember what post they're under.
Good luck.
~Ken~

Yep, they'll be always wet, since they're on a floating raft and the bottom of the pot punches through it.

Thanks for the tips. :)

I also agree that it would be best to aerate the nutrient solution. If you measure right, I see no problem with your setup plans. being that you only plan the very bottom be in the water allowing the growing medium to wick up the moisture. But There wont really be any way to keep the roots from growing down into the solution.

The lettuces plants I grew had roots that hung down more than one foot below the 3 inch baskets that I use. And that's the smallest plant you plan. I have grown tomatoes in a 2 gallon buckets, granted not dwarf tomato's. But I wouldn't grow tomato's again unless I have 5 gallons of root space for each of them.

I have also grown bell peppers in two litter bottles, but root maintenance was a problem with clogging the neck of the bottles as they grew down into the pipes. I now know that at least one commercial operation gives peppers 3 gallons of root space. Bottom line 4,6,8,12 inch pots, the roots will undoubtedly grow into the nutrient solution regardless.

You don't need larger than 2" net pots for anything, except maybe a tree. A tomato (or maybe pepper) unsupported will need to be top suppported, but as they need to be anyway, its a generally moot point. The roots will grow through the slots in the pots and down into the water.

This may be the picture hardclay mentioned above:

Very interesting. A very impressive mass of roots indeed. :) As a (historically) soil grower, I never get to see anything like that except the roots that grow out of the bottom of pots that are in trays that have water in the bottom much of the time.

Now, wouldn't any adventerous roots that grow down into *un-oxygenated* water simply die, and the ones in the vermiculite remain? Sort of like how roots of a plant in a pot that's not in a tray of water seldom venture far from the bottom of the pot?

Probably to some extent. but lettuces don't have extensive root systems and if you're intending to grow tomatoes un-aerated then you'll need at least a 10" pot and still need some luck on your side. the full grown tomato plants had probably 4 times the root mass of that shown above.
adding a simple air pump doesn't cost much or muddy up the system substantially but it will vastly improve your options as far as growing.
So if you're in a third world country and electricity is really unavailable, then by all means leave the air pump out. If you're just being cheap frugal well janis stated it best when she said "nothin' ain't worth nothin', but its free."

OOC, how big were your toms when fully grown? The type I'm growing supposedly maxes out at about 2 1/2 feet.

Yes, That's the picture grizzman. It describes to a new comer the concepts of Hydro/aero root irrigation better than words. If My memory serves me, that was a combination DWC (Deep Water Culture) system utilizing a vortex sprayer & sub aeration?
Like many designs, such a system requires little in the way of net pots or medium other than to support the plant upright. Cloning systems simply use urethane plugs to hold the plants upright as they aren't expected to support much weight.
If I have been understanding karenrei correctly, the system she has been describing sounds like a combination of floating raft & SWC (self-watering-container) concepts, therefore requiring large net pots like you suggested because they will be doing more than holding the plants upright as this is where the roots will be absorbing O2 & moisture also.
Maybe a better way to describe it is like this; in soil a plant drinks when it's watered and breathes as the soil drys out. In hydroponics (except for ebb & flow/flood & drain type systems) the Plant drinks and breaths at the same time.
I use ultrasonic fog & sub aeration/DWC. Some use high pressure spray (aeroponics) or low pressure (aka sprinklerponics). In NFT the solution is always flowing, allowing it to absorb O2 as it travels. Many of these systems also use sub aeration either in the root zone or in the reservoir. Some systems even utilize the air to propel the solution upwards (aka airlifts).
Regardless, we don't always all agree on everything but I think we're united on this one - a cheap to buy and cheap to run aquarium air pump will give karenrei's system what it really needs, O2 and motion in the lower root zone.
Good luck to all,
~Ken~

Good grief grizzman that root system is rediculous !!! Oh by the way this is a long shot but grizzman I think I spoke to you in an email a couple years back and the only thing I can remember is you said you live in Rcansaw jk round with ya ... Anyway nice maters though !!

hardclay; that system is a DWC/ soakaponics (name aptly taken from hex) system. the only aeration comes from the sprinklers.
When I run NFT, I don't use an air pump. the only aeration is the water falling back into the rez.
karen the plants were 6' to 7' tall at their demise. the plants shown above are only 18" or so tall. IF I put all those roots into a 10" pot with hydroton, thywould only just fit. I can't imagine a full grown plant (even a dwarf) bearing fruit would have less roots.
BTW, you might want to look into smart valves. I've been pondering a non powered EnF system using the smart valve concept, though I haven't worked out the kinks yet. there would, however, be some physical labor required to lift the nutrient from the low rez, back into the high rez. My thinking is this system would benefit arid 3rd world countries where electricity and water is a rare commodity, but manual labor is abundant. Once (or if) I get a working prototype, I will post details. (it's kind of taken a spot on the back burner for now)

Heh, my next "upgrade" will be an automatic PPM-maintenance system. The idea is to connect the main reservoir via dialysis tubing to reservoir of a constant osmotic pressure connected to the main reservoir. Constant osmotic pressure would be maintained by a high molecular weight substance, such as long-chain PEG or perhaps starch (amylose or amylase) which cannot pass through the tubing. So long as the water level was maintained and the substance didn't break down, the osmotic pressure should remain constant. Water level could be maintained by a float valve similar to that which sets a particular water level in your toilet.

Note that this wouldn't self-balance the ratios of particular minerals in solution (I've thought about systems to do that, but they get a *lot* more complicated, and generally involve reverse-osmosis filters and/or ion-selective membranes). But this simple system should at least keep your ppm levels even.

But for now, I just want to get the initial setup going. :) I'm still lacking my pots (although they should arrive any day) and I haven't gotten my water quality report (although I suppose I could just start off with distilled and/or rainwater and then switch to tap and adjust my nutrient levels once (if?) the water department sends me the report)

This is a picture of a chile grown in an aero system for 6 mos with no root pruning.

Pot size really doesn't matter in hydro....use what's convenient.

Holy crap!