Rosemary: The herb with winter problems
Cold, dark winters are a challenge for keeping a rosemary plant alive for next spring.
“There’s Rosemary, that’s for Remembrance.” The herb rosemary is grown each year in many home gardens. It is an attractive, narrow-leaf evergreen shrub. It grows well during the summer in Michigan but has confounded many gardeners on how to keep it alive for the rest of the year. No matter what they try, they cannot get it to stay alive over the winter.
Rosemary (Rosemarinis officinalis) is prized as an herb with a powerful flavor and fragrance. When used in cooking or baking, a little goes a long way when adding flavor. Gardeners often would like to either have it be alive in the spring outdoors or dig up the plant and bring it indoors. But no matter what they try, the plant is dead before the first daffodil blooms.
Why the plant is so difficult to manage goes back to its origins. It thrives in a Mediterranean climate that offers bright, hot sun, sandy, well-draining soils and temperatures that don’t dip much below 30 degrees Fahrenheit. During the winter months, it prefers cooler temperatures of 60 to 65 degrees during the day and 40 to 50 degrees at night. The light needs to still be bright and the air should be damp. Circulating air helps prevent fungal diseases like powdery mildew.
It now becomes abundantly clear why leaving it outside in the garden ends its spicy life. It is considered to be hardy in Zones 7 to 10. That’s climates like North Carolina, Texas and California. A large part of Michigan is rated Zones 4 and 5. That indicates that the winter temperatures could dip to -10 to -30 degrees.
When rosemary is potted up to come indoors to play houseplant, the temperatures that humans seek for winter comfort are too warm for it. Rosemary does not get that cool resting period it requires. It is either over-watered or left to dry out too much between water applications. And Michigan has so much cloud cover during the winter that the plant is often light-deprived.
Those blessed with a minimally heated greenhouse have the best chance of success. The rest of us just buy another in the spring and begin again.
When Shakespeare wrote, “There’s rosemary, that’s for remembrance,” he meant it to refer to the belief that rosemary helped the memory. But now it could be interpreted to mean that by spring, all we can do is remember the plant when it was alive.