Do you have pics you can post Sam? Here is a pic from my Romaine Lettuce grown in an aerospring
{{gwi:1012805}}

As you can see this is almost a fully grown head of Romaine, approx 35-40 days old grown under a 400 MH and 250 watt HPS HID light - total 650 Watts. So, do your roots look similar on your lettuce? I built my aerospring according to the book "How to Hydroponics" and built 2 of them, and joined them together to grow lettuce and other herbs.

More links on my website and photos

-Eric
TechnologyGarden.net

Ok, here are two pictures. I failed to write in my log the exact date these were started. But about 10 days from seed.

I have lowered PH to 6.4 - 6.6, EC at .7, temp at ~80. And a 4 Foot 4 Lamp High Output T5 Fluorescent Grow Light. A link to my light is listed below.

{{gwi:1012806}}
{{gwi:1012807}}

Here is a link that might be useful: My Light

You see those little short roots sticking out of the cup? Those will get a lot bigger really quickly.

I know what you're talking about though - I've had some plants (mostly spinach) that have really narrow, long root systems rather than the huge furry mass that some of my lettuce plants like to grow.

What I'm going to experiment with is intentionally crowding the roots early on. I usually start my seedlings in a Jiffy Starter and it seems (I could be wrong) that if I leave them in that sitting in a tray until the tap root hits the bottom and goes sideways that I suddenly get loads of roots coming out the sides of the Jiffy.

That'll make for a faster developing and more robust root system later, I think.