Experts and BHG readers answer.
Rosemary over wintering
Thanks for writing. Rosemary can be tricky to keep going all year. Keep in mind that it is a Mediterranean plant -- and as such, it likes it on the dry side. The most common reason indoor rosemary plants fail is that they're watered too much. It's best to let the top couple of inches or so of the soil dry between waterings.
Also: Make sure your rosemary gets plenty of light. In your area, they can take direct sun from a south- or west-facing window.
Keep an eye out for disease, too. It's extremely common for rosemary to suffer downy mildew, a disease that looks like there's white fuzz growing on the leaves. If you see downy mildew, cut back on the watering a bit and run a fan near the rosemary to help provide good air circulation.
I hope this helps. Good luck!
---Justin, Senior Garden Editor, BHG.com