Yes, rosemary is a rosemary perennial that returns each year in warm places. But your plant's survival depends on where you live. So does rosemary return yearly for you? Your USDA hardiness zone holds the answer to that question.
I have grown rosemary in both zone 8 and zone 6 over the past decade. The difference is stark. My zone 8 plants thrive outdoors all year with zero protection needed. They grow into large shrubs that reach 4 feet (1.2 m) tall and get woody at the base. My zone 6 plants need serious winter help or they die back to the ground. Without mulch and frost covers they do not survive the cold months at all.
As a rosemary evergreen plant it comes from the warm coast of the Mediterranean. In its native home it never sees hard frost at all. The leaves stay green year round and growth continues through mild winters. This origin explains why cold is the enemy. Temps below 20°F (-6°C) for long periods will kill most types. Even brief dips to 10°F (-12°C) can cause major damage to stems and roots.
Two terms help explain how rosemary behaves in your garden. True perennials survive winter outdoors no matter how cold it gets. Tender perennials like rosemary can live many years but need help with hard freezes. In warm zones rosemary acts like a perennial. In cold zones it acts like an annual unless you protect it from frost.
Find your USDA zone on the official plant hardiness map if you do not know it yet. This free tool on the USDA website shows the average coldest winter temp for your area. Once you know your zone you can plan your rosemary perennial strategy with confidence. Knowing your zone saves you from buying plants that will not survive your winters. The map also helps you pick the right variety for your spot.
For zones 8 through 10 you can plant rosemary in the ground and forget about winter care. These plants will come back every spring without any help from you. They may even bloom through winter in the mildest spots. Choose any variety you like since cold hardiness does not matter here. Your rosemary will thrive like a true perennial for many years to come. Just give it good drainage and full sun.
Gardeners in zones 6 and 7 should pick cold-hardy types like Arp or Hill Hardy. These tough cultivars handle temps down to 5°F (-15°C) with some protection. Pile 5-6 inches (12-15 cm) of mulch around the base in late fall before the ground freezes. Add a frost cloth cover during the worst cold snaps. Position plants near south-facing walls for extra warmth from reflected heat. Check on your plants after major cold spells to see if they need more cover.
If you garden in zone 5 or colder then grow your rosemary in pots instead of the ground. Bring the containers indoors before the first hard frost in fall. Place them near a sunny south-facing window and water sparingly through winter. Keep the room cool if you can since rosemary dislikes warm dry indoor air. Move them back outside after the last spring frost passes. With this method your rosemary will keep growing as a perennial for many years. You can enjoy fresh sprigs in cooking no matter where you live.
Read the full article: Rosemary Plant Care: Complete Growing Guide
