They are coming in quart sizes, probably at most about 10 or 15 inches tall, just babies. Do you would it be overpotting to up them to 12 inches? And do you use regular potting soil, or cactus mix?

What they come in is because it makes sense for shipping, etc. I still think it is better to put them in a larger pot - more forgiving for drying out, etc. I used a better quality potting soil.

I see. I was worried because what I read was saying that if you overpot, they might have too much moisture. I live in a relatively moist climate, but it does get cold, hence the pot. So I could probably do a 12" but just be careful not to oversaturate the soil. What do you think?

I wouldn't worry about your moist climate. Baytrees grow happily in the ground and in pots over here and there is certainly no lack of moisture. I agree that a 15 inch bay needs a decent sized pot. I'd start it in 12 inches. How cold do your winters actually get? Bay isn't tropical and can take light freezes.

We get hard freezes and temps below -5 before windchill so I definitely have to overwinter indoors. Bay is only hardy to zone 8 and I'm in 5.

Thank you for your help!

-5c would not worry it but -5f is a different matter. Definitely too cold for bay. But don't worry about rain.

Lol I meant -5f. Much too cold for bay. (haha, my SO is referring to them as "bae's bay") And that isn't even counting the wind chill so they definitely wouldn't handle it.

When I used to try them indoors in pots they would never really thrive as I mostly underpotted them (as trees) they can handle larger pots as long as they get the sun they need. Since then, I planted some in the ground in zone 7. They usually are fine and even will come back from roots after a very bad winter, but 5 is not so doable in ground.