Derek Turner wrote:
I've looked in the garden shops here in Cornwall, and I haven't seen
anything in their stocks that would be suitable.
Use the Unwins seed tapes. Easier to plant and no need to thin. Ditto
parsnips, leeks etc. For salads use the seed mats.

For leeks, I sow them into root trainers in little pinches, then when it's
time to plant them out I separate them by giving them a bit of a knock and
all the soil falls off and they can be put into individual holes.