How To Care For Rosemary Plant Outdoors. Dry indoor air especially in winter can make growing rosemary indoors challenging. The answer depends on your growing zone as rosemary plants are unlikely to survive temperatures below 10 to 20 F.
-7 to -12 C. Rosemary grows best indoors at cool temperatures preferably around 60ºF. It needs 6 to 8 hours of bright sun each day.
The key to growing healthy and thriving rosemary plants is to keep the plants in a bright sunny location keep them watered but not soggy and to routinely prune the plants to guide their growth.
Regarding the irrigation the rosemary prefers drylands not very watered. Improve the drainage of your soil by amending with sand or grit to prevent damp soils which risk root rot. If your rosemary plant is suffering from the winter damage or fungal infection prune the damaged dead and crossing stems until the living wood or first set of healthy green. For a head start plant the seeds or cuttings indoors 8 to 10 weeks before the last spring frost.