Rosemary (Rosmarinus officinalis) is a must-have garden plant for me. I use this herb frequently in cooking, and I love the look and scent of it growing by the back door. In my Maine garden (USDA winter hardiness zone 5a, with typical winter low temperatures around –20 F), this plant must be treated as an annual, as it can’t survive our cold winters. (Some recommend growing it in a pot and bringing it inside in winter, but my occasional attempts at doing this have never been successful.) In my zone 6b Gettysburg, Pennsylvania garden, however, this plant could be thought of as a tender perennial. Local gardening lore is that it will survive down to about 20F and can be wintered over if given protection on colder nights.
Over the years, I have often tried to protect my rosemary plants from those cold winter temperatures – but never successfully. One year, for example, I kept a box by the patio door and would put it over the plant on cold nights. Inevitably, however, I missed one night and the plant perished. In this way, I have always ended up starting over with a new rosemary seedling each spring.
Last year, however, we had such an exceptionally mild winter that the temperature apparently never got down below 20F, and my rosemary plant survived. I was amazed by how large it had grown by the end of its second summer in the garden; suddenly those mythical rosemary hedges of milder climates seemed more real. And so, when a blast of arctic air descended over much of the eastern United States this week, bringing the coldest temperatures in over two years to my Gettysburg garden, I was determined to try to save my rosemary plant.
Recently, Noelle of the blog AZPlantlady posted advice for desert gardeners about how to protect their plants from freezing desert nights, and I decided to try to adapt Noelle’s advice to protecting my rosemary. So, when I got home from work on the night that the arctic air was predicted to arrive, I started looking around for something to cover the plant with. I would have been tempted to use a large dry cleaning bag, but Noelle warned against plastic, which she advises transfers cold to the plant rather than protecting it from the cold. I thought about using an old towel, but realized it wouldn’t be large enough. What I really needed was an old frayed bed sheet – but I didn’t have one and wasn’t willing to sacrifice good bed linens to the cause. Finally, I came upon an old nightgown, recently retired and waiting to be cut up into rags. It seemed as though this might work. I took the long sleeves of the nightgown and tied them around the neck opening to close it off; and then I took it outside and, by the dim glow of the patio light, draped it over the plant, trying to tuck all the branches under the protective covering.
I didn’t succeed in following all of Noelle’s advice. In the light of day, it became clear that I had not covered the plant completely and eliminated all gaps where heat might escape. I have also not been able to remove the covering during the day to expose the plant to sunlight and warm air as Noelle recommends, because our daytime highs have only been in the teens. Tonight will bring our fifth night in a row of frigid temperatures, but a warming trend is expected beginning tomorrow, which will allow me to remove my rosemary’s nightclothes. Will my efforts bring my plant successfully through the winter cold? I probably won’t know the answer to that question until spring. But there was nothing to lose by trying.