Jayne said:

I have pumpkins of all sizes on my 3 plants. Several of them are quite big
now, but as this is the first time I've grown them I'm not sure *when* to
harvest them. I've read that they need to be "hardened" before storage, but
when do you know they are ready to be picked?
Any tips appreciated!

Same as squash. Leave them on the vine as long a possible, and pick before
hard frost threatens.

The stems should be hard (like very hard wood). The rind should be tough
enough that you can't pierce if with your thumbnail.

You can't reliably go by color (particularly with carving pumpkins) as some
have been bred to color up early and may be orange long before they are
hard enough to last well off the vine.

--
Pat in Plymouth MI

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)