Zone 6a on the coast.

So I've read Eliot Coleman's Four Season Harvest and I'm all ramped up to go for a winter garden. Here's my dilemma it's mid September here and my summer crops are still going. I've never had to make the choice of when to pull a plant at the end of summer. Some I'll keep to the bitter end like tomatoes, tomatillos, pumpkins.

But what about Eggplants, summer squash, peppers and other heat lovers? They're still blooming and have small fruit. When do I call it on them and start getting fall seedlings into the ground? Thanks.