Jens, we've had really poor luck with starting seeds indoors. We try it every year and it just seems like they get too tall without any bulk to them so they don't have any strength when we move them outdoors. Part of it I'm sure is the light indoors, we set them in windows but our house only has windows on the east, north, and west, our garage is on the south side of our house so no south windows to start seeds in, that means we can only give them a little sun in the morning or in the evening. I bought a small LED to try starting seeds a couple of years ago but it wasn't powerful enough to make a difference (it's actually hanging in the greenhouse over the second fish tank that isn't connected because I was using it on my test system over winter to try and give the plants a little extra light, but I think if I have to run supplemental lighting in the winter I might invest in metal halide lights because they would be powerful enough to grow the plants plus give me extra heat to warm the greenhouse... I will probably wait another year before I decide if I'm going to add supplemental lighting for winter or not. I need to get my solar panels built and installed before I add that though so they offset the electric required to run them so my electric bill doesn't get any higher.
This year having the greenhouse we're starting all of the seeds in the shelf above the growbeds so the seeds didn't sprout quite as fast as they would have indoors because the temperature is still a little lower than inside the house (and I'm still waiting on most of my tomato and peppers to sprout because I think they want constant 70F or more before they really get started), but it will hopefully reduce the shock for the plants we move outdoors... the stuff that started in AP will probably stay in AP through the summer just to see how they do and see how hot it gets in the greenhouse. I think it might stay 75F in there max until the outdoor temp gets above 75F because Sunday it was about 72F and the indoor temp stayed 75F, so it might not get too scorching hot in the greenhouse having the water barrels to help cool the temp for summer. Our average high at the hottest part of summer is only 82F, while the average low that time of year is only 60F, so it might be quite pleasant inside the greenhouse in the summer if it manages to stay a little cooler than outside the greenhouse.
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The greenhouse outside dimensions are about 16ft x 16ft (4.88 meters x 4.88 meters), so it's an OK size, not the best layout, but better than nothing. I think if we are fairly successful with this greenhouse I will either expand it or build a larger hoop house in the future... even if the expansion or hoop house were only used for spring/summer/fall season extension and the smaller greenhouse is used for winter growing would be OK.
scotty, I think the lettuce I'll continue starting right in the gravel bed because they seem to start really well in the bed. Everything else I may end up starting in seed trays then transplant them that way I can sprout them indoors or higher in the greenhouse where it's a little warmer (but I'm sure the reason everything else didn't sprout quite as fast is that the water temp is still only about 55F when I test the fish tank water every couple of days), then move them in to the AP system when they are ready to be transplanted. I still have a lot of work to do with the greenhouse, I'm just getting burned out. I wake up at 5am every day to go to work by about 5:30, then work until 4pm, go pick my son up and spend 2 hours with him before my wife gets home around 6pm, then by the time we eat dinner it's 7-7:30pm, then try getting the kid to bed by 8pm, then I do my chores between 8-9pm and I try to get to bed around 9pm so I can get up and do it again by 5am the next day... really my only time to work on projects is the weekend and now that weather is getting nicer we're going to get to the busy season of family get togethers, mowing the yard, my scuba diving season, all of the good stuff... so my projects will probably be pretty slow over the summer (although I'll probably start cutting back on my hours for the summer so I won't go to bed quite as early might give me a little more time to do things at night).
Brian, I'm great at starting projects... not so great at finishing projects =) my wife can't stand that I have so many projects active at one time, she would rather I just finish one project before moving on to the next project, but I get bored working on the same thing all the time, plus some projects are better for nice weather while other projects inside the house are OK for rainy weather etc... eventually I'll finish all of the projects... maybe =)
If your lettuce is starting decent but then dying off when you move it to the DWC I would probably look at getting it more light too. You could test it even with a cheap clamp light and spiral CFL bulb (or if you still have old incandescent lights). There was a rather interesting post on plantedtank forum that I've bookmarked talking about PAR, and surprisingly if you use a clamp light so it has a decent reflector on it spiral CFL bulbs are capable of producing quite a bit of PAR for plants in water... so I would think you could set up a test fixture over part of your DWC to see if giving them more light would help them or if not that might tell you something else is going on and keep you from buying fluorescent fixtures that might not be your problem. Seems like you are far enough south that you would get a lot more sun than we do, you haven't put your shade cloth back on for the summer yet have you? I had fungus gnats in my system pretty heavily when I first planted all of my seedlings but they didn't seem to really hurt anything even though they say they will eat the seedlings and kill them... I put out some sticky traps that seem to be working well for the gnats, so hopefully their larvae dies off too once there aren't as many gnats to produce more larvae.