Unless you have a seriously dark shade house I would think you would still have more light than indoor under a light. How about the differences in temperature between the shade house and indoor under lights?

It is hotter I shade house than inside, shade is 50% we grow lettuce in there in the summer.

Rio - If you are having trouble sprouting lettuce in the rockwool cubes, then I would pre-sprout the seeds in a dampened, folded, paper towel. Be careful to not keep it too wet or let it dry out. Transfer the seeds to the cubes when you see the seeds wanting to sprout. Then put a little vermiculite on top (in the cube well). Hope that helps.

Sprouting isint an issue. The biggest problem is they get very leggy. Tiny stem and tall. I see others that probably don't have 3/8 in stem but are at the 4 leaf stage.

I am sure they are starting in a cooler environment than mine. Usually leggy means lack of light, but the plants in dirt under the shade don't have these issues.

Rio - If light isn't the problem then it must be the heat. Even with heat tolerant varieties all I can get is thin leggy lettuce seedlings growing my Tower Garden this summer. I'm giving up until fall.

I am thinking I may start the next batch in the basement 50 some odd deg under a fluorescent light with grow bulbs in it. Worst case they look like these. Some of these starts are so leggy they can't support the leaves that are forming. We will see what happens with this batch.

My lettuce start always looks leggy too whether I start them under lights or in a sunny window. Once the start get into the system in about a week, they really start to pick up and form new leaves.

Could be I worry too much, it has happened before.

What temperature are the rockwool cubes and the air temp?

Not sure on the rockwool, but the air temp swings with the time of day I rarely see it above 80 during the heat of the day,

80 sounds high. I've been doing a lot of reading, as I'm just starting lettuce this week...

Here says
http://www.howardresh.com/Hydroponic-Lettuce-Production1.html

Also, from here:
http://www.ecaa.ntu.edu.tw/weifang/lab551/vegetable/culturalpractice/ten%20years%20of%20hydroponic%20lettuce%20research.pdf

They say you can have air temps around 75f (24c), but only good growth (with no shooting, to seed, I assume) if nutrient is kept 68f (20c).

I am in a semiTropical environment. We start the lettuce at the edge of our covered patio facing South. That would be North for those of you above the equator. We do this all year long, and we get maybe 2-3% that have your problem. Temp doesn't seem to make any difference. Our seedlings go from our germination station on my patio into the NFT system in full sun in less than a week typically, but no more than 10 days ever. We don't do any pretreating of the rockwool, and just set the rockwool in a nutrient mix that is 40-60% dilute off our regular nutrient tank

Hope this helps,

Thanks for the replies, I am going to try nutrient in my latest batch, we were putting in a 50% mixture but not before the 2 leaf stage and we don't allow them to sit in any water. It seems awfully dry to me, but this was what I read. I agree the water needs to stay cool, but until they go into the system this isint an issue as we keep our nutrient jug in the house.

I am experimenting as I go, we just haven't been able to get weekly predicatable transplants.

Two additions to above. Use something like RapidStart instead of "nutrient" because it has hormones to promote root growth. Start in the dark. Light as soon as leaf (about 36 hours for us).

We've done it many times with many varieties using RapidRooters on heat mat set at 78 deg F. Sprouts in 24 hours and transplant in 7 days. We've always been soil based until this time (see recent post on starting Aeroflo).

i ve heard on here that putting them inside in the ac at night will thicken them up