How long should I leave Greek Oregano, Parsley and Chives?

You can leave them until the first frost or freeze kills them, or you can put them in appropriately sized pots and bring them into the house to overwinter them under plant lights. Chives will probably come back if you leave them in the garden, just cut the chives off and dry or freeze them for winter use. I usually only bring in my rosemary for the winter. I cut it back some so that it doesn't end up too big by spring and get leggy. I usually keep it for two or three years, after that they start to get old and woody and don't stay filled out as well with new branches.

You could dig up and bring in side

I live in Oregon near Portland. I have had a chive plant in my garden for about 10 years now ( it abou a 2’ * 3’ patch) all I do is trim it back to about 6” from the ground in the fall,

and cover the bottom with lot of soil. It comes back ever spring!

I always had my oregano, mint and chives come back every year in my veggie garden and I never really did anything to them that was special, just covered with leaves like I did the rest of the garden. I now plant them in pots, they tend to get out of control in the garden. My mint and oregano got to the point that by the end of the season they took over almost a quarter of the garden and each fall and spring I would spend hours digging up mint plants and paring down the oregano patch. I get much colder than you do during the winter, so yours should come back. Just make sure to dig up stray plants that show up in the spring. Chives can get out of control, too, if you don't take care of the flowers before the seeds dry up and fall all over the garden.