[biosolids]

I planted several 'unknown' marrow type plants, and now have plants producing fast growing spherical fruits (green, with courgette texture skin).  How can I tell what they are, and when do I pick them.

[David.]

If they are bush plants, probally a ball courgette. Pick when they are the size you want (slicing or stuffing), before they lose their shine.

If trailing and with dark, streaky green fruits they could be Halloween type pumpkins (which turn orange).