Planting Salad now?

Hi.

I'm wanting to get some late lettuce on the go.  Would there be time for sowing from seed or better to get some 'living lettuce' leaves in a tray from a supermarket?

TIA

Adri

I sow now to put in pots in a few weeks to go in the polytunnel overwinter where the tomatoes have been taken out. They last until its time to prepare the ground to plant tomatoes again. The only problem is that it gives greenfly somewhere to overwinter.