Any pics to share? That is needed to tell you more about your plant but the most common and *vigorous* oregano is common oregano, Origanum vulgare.

FataMorgana

I have researched and believe it to be greek oregano. It is hairy and has that bite to it.

Sorry - no pics! It stood quite tall - maybe not 3' as now I think, it was in a raise bed of 12" - with purple flowers.

I thought Greek oregano had white flowers.

Mine here in NH zone 5, stays small. From your description you have the common variety and I would pull it all out if I were you.

oh no! Will investigate further then, thx defrost!

OK - have found several site saying the flowers are white, one saying white flowers are marjoram and purple oregano, and another saying greek oregano can have pink, white or purple flowers...

Where can one find a definitive answer on this?

This was my Greek Oregano(started from seed)late in the season. HTH

My common oregano looks like the plants/flowers in the link below. Pinkish-purplish blooms, can get 2+ feet tall if I don't keep it clipped, and it vigorously spreads as it wants through the garden. It is a hairy plant - not completely down covered like common mullein but enough hair that you see it on all the stems and leaves.

It has a nice spicy oregano flavor and the vigor is wonderful if you want to harvest it for kitchen use for you and 20 of your closest friends! :)

FataMorgana

Here is a link that might be useful: Oregano

that seems to be what I have - shoot! I wanted the greek kind....

I have Greek oregano and it loves to spread. From a 3 inch pot to a 4 foot by 4 foot bed. Anytime I find a friend who would like a plant I pot up some as it can spread over the complete area if allowed to do so. The French have the right ideal when using fresh herbs in cooking they just tie a string around the bundle and put them into the pot with the end of the string hanging outside the pot to be removed later. It does need to be trimmed each year if I do not use it enough. Even here in the Houston area it will die back if we get cold enough weather but will jump back up during our spring season when ever that may be usually about the middle of February?

Luckily a lot of Italians live in Chicago. They LOVE Oregano for sauces. Better go find some Italians to help keep it in check.