Not sure where you are, but I'm also in zone 8 and rosemary is a perennial here, evergreen. It sounds like yours is in a pot. Do you have a piece of ground where you could give your rosemary a permanent home?

Rosemary will take a freeze and certainly won't be bothered by 50 degrees. 50f will not 'stunt its growth' any more than winter 'stunts the growth' of any evergreen. In climates where it is hardy it will obviously stop growing in the winter but it will remain evergreen. You don't actually want it to grow actively in the winter because fresh growth is more likely to be killed by sub freezing temps. Even if your climate has prolonged low sub freezing temps you should try to have your rosemary outdoors as long and as often as possible weather permitting. It is not a happy indoor plant.

I live in Northern Alabama where the winter temperatures always hit the low teens in the winter. Rosemary is often planted as an ornamental shrub! It's a really an evergreen woody shrub, and is quite hardy....certainly in a zone 8 climate.

We've had winter temps in the single digits and had some top die back, but the plant came back stronger than ever in the spring.

If you're growing it in a pot, it will probably survive better if you bury the pot in the ground for the winter up to the rim than if you simply leave the pot outdoors above ground.

I never have any problems overwintering Rosemary in my WET/HUMID Zone 7. They have even become hedges and flower annually--despite last winter's COLD/WET & SNOWY conditions. I would suggest you plant them in a sandy, well-draining soil in full sun if planted outside.--Southern exposure in a raised bed is ideal. Zone 7 seems to be cold hardiness limit otherwise they are carefree and easy. And, do not fertilize them--they like low fertility soils.

I'm not sure how cold rosemary can get, but mine is in the group year-round, and it gets close to freezing in the winter. Rosemary is used in landscaping a lot in zones 9 and 10.

Here is a link that might be useful: What's Growing On?

The cultivar Arps is said to be hardiest. I have planted these and unnamed varieties without problems. In the worst of winters, you might get some minor die back in zone 7 but they quickly recuperate. My winter MINIMUMS are in the upper teens on average but average minimums are in the mid/upper 20's during the coldest months but it can get down into the single digits on occasion--and they have been completely buried in snow for days on end. As a houseplant, they ALWAYS died on me so now I don't hesitate to plant any Rosemary variety in the ground--especially as they the local deer HATE them and don't do them any damage--ever. If your zone is marginal and you are concerned, then plant in a warm microclimate. You'd be surprised with how much you push gardening zones but exploiting protected areas around your home. Good luck!

I know this question was from 9 yrs ago but I found myself googling this same question and found this post.....whether to bring mine in tonight.

I think most commenters misunderstood the question asked.

I don't see anywhere that the OP said anything about it being winter.

Like me.....it's springtime and our weather has been unusually dipping down in temps that's not normal.

I managed to keep my potted rosemary alive over this last winter and brought it back to life, trimming back the stalk it became.

I started having new growth along the stalk and it has been flourishing for the past month, filling in beautifully.

But our weather has been dipping down to 40-50 degrees off and on and I, too, wonder if I should bring it in to protect the new growth. Because they're just babies!

I don’t think anyone misunderstood the question. However, be that as it may, the answer remains the same. Rosemary will not be fazed by temperatures in the 40s or 50s. Obviously, if it’s been inside all winter it will need hardening off but thereafter it can stay outside. But yours has been outside for a month so it'll be fine.