Oh that's a gem of a pot. I would treat it very carefully. You only need to seal the interiors if you intend to use it to hold water, but as an olive jar, wouldn't it already be sealed? In anycase, I don't think it's necessary.

Can it not be used as an outer container for a smaller pot.
If it has a narrower opening, can you not set a plastic containered pot in it? or place a stand inside the pot so you can set the smaller pot on it. Otherwise you'd have to fill the entire pot with soil which would be wasteful. No root system will get that far inside and besides conditions would be anaerobic at that depth.

Ianna

thanks ianna...I have placed a smaller pot inside the top of the jar (the rim of the smaller pot just sits on the lip of the olive jar. I didnt have any trouble with it a few years ago when I did it, but I do worry about watering it and having the water drip to the bottom and sit there (in case it weakens it).
It's not a "real" olive jar. Its terra cotta, in the shape of the old olive jars of Italy. It has two worn handles on either side and its really one of my favorite items in my outdoor garden. Im guessing like you said, real olive jars would be sealed.
Thank you for your help!
Keekush

Hi there keekush;

You are so lucky to have found such a gem! My advice, however, is not to leave it in the garden through the winter. If it has done well on your screened porch...replace it there for the winter. Zone 5 winters tend to damage terracotta, some more than others depending on how they were made. I wouldn't take the chance. Enjoy it in the garden this season and protect it through winter.

Thanks joy4me. I do bring it in faithfully each year. Im originally from the southwest and discovered one year when I DIDN'T bring in my terra cotta pots from the snow, they crumbled in the spring. Yeah, I wasnt happy. Live and learn!
Now Im off to find a nice flowering/trailing plant to sit on the top of my pot.

no need to coat terracotta before putting outside.
don't know what look you're after, but if you like the look of green moldy/mossy on the outside, that would probably happen on its own if it were in a moist shady spot. orif the pot were in the sun, you could paint it with a buttermilk/moss mixture to promote the lichen growth.
best, mindy

Thanks Mindy,
I do like that look (with the lichen)but this pot/jar has a satin like coating so I think thats what stops the forming of moss. Its not coated on the inside though so Ive taken to just sitting the plant on top of the jar (with s slimline drip dish) and its doing ok. Thanks for your suggestions!