Ophelia wrote:
I always start cucurbits off in pots and, if I start early and summer
is late. they can end up being quite big (and in biggish pots),
I start my Phaseolus beans in paper pots, too.
So, it was nothing to do with transplanting into bigger pots then? Hmm I
know I was late sowing ... I might try again next year. When is the best
time to sow the seeds?

I normally sow mine starting end of March, indoors, then some more in
April. And probably some more in May. And if any failed, then maybe
a couple more in June.