A week or so back I bought some Cos lettuce plants from a local nursery.

They are growing well and fast in the 'raised bed' bags but so far they
don't look like the picture on the label :-)

At the moment they are more like a leaf lettuce than a heart lettuce - but
it looks as though the heart is beginning to develop.

If this carries on, I think I will have a lettuce heart and a more or less
redundant ring of leaves around the base.

So when can I pick these outer leaves for an early crop without
compromising the forming of the heart?

Cheers

Dave R