Hi Dave,
I think it is nothing you are doing wrong, it’s just the weather. It is so cold and so little sun. My seedlings I have put in the ground are doing very little, so far. I am cloching them at night with plastic bottles cut in half to keep the slugs at bay. It’s a pain putting them on and off, but they are not getting eaten.
My lettuces in modules, even in the polytunnel, are still very small. I think the plastic greenhouses offer shelter from the cold winds but still very cold at night. The forecast does not offer much cheer for the next days either.
You might try a bit of fleece over them at night. If your soil on the plot is still very cold, they may not fare well planted out just yet.
Some peoples do rain dances, we need to do sun dances and get the temperature to rise!
