I have a few 'Cupani' Sweet Pea Grandiflora that are now about 1½ ft. tall,
growing up a trellis archway. I understand that they will, in time, grow to
at least 6ft. Do I need to pinch the tips out, as I would on the taller
varieties, or should I leave them to get on with growing un-pinched? I
wouldn't want to harm them in any way. Please advise.

Thank you
Martello