On 2 Feb, 12:04, michael wrote:
I sow seedlings in small pots of plastic trays,and although very
careful with watering,I always seem to get problems with damping
off.It starts with just one or two then spreads quickly.I have sown
onions and lettuce to date,and briefly describe what I do to minimise
the problem.

(snip)

Why do you add the perlite on the top? It expend twice it's size and
that's where you go wrong I think. The water get logged there, at the
stems of your seedlings and creates a wonderful moist place for
bacterias. I would mix the perlite with the compost you make and
wouldn't water again from below, but from above once you see the
surface dry. Also you might have confused vermiculite with perlite -
vermiculite gives air to the compost and maximise aeration for the
seedling growth. Perlite speeds up rooting but mixed in with compost,
not put on the top only. I've never use copper sulphate.