Overwintering Rosemary in the North

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Click To Enlarge Photo: Jennifer Blume

by Ellie MacDougall
October 1997
from issue #11

In southern Maine, where Zone 5 temperatures fall to –20°F, I tried many ways of coaxing rosemary through the winter before settling on the following:

I select a few stocky plants to overwinter. Around mid-summer, I prune them lightly to encourage short, bushy growth. Then, before night-time temperatures start falling into the 40s, I pot them up, leave them outdoors for a few days to acclimate, and bring them in before the deepening cold induces dormancy.

They live in the back hall where temperatures are in the 50s, and they receive 5 or 6 hours of bright, indirect sunlight. If growth is leggy, you can supplement natural light with fluorescent. I water when I remember to. It’s important not to overwater, as rosemary is prone to root rot and, equally nasty, powdery mildew. In the spring, I harden them off and set them back into the ground.

I wouldn’t recommend trying to overwinter rosemary outside in the North. Heavy mulching in unheated greenhouses and cold frames can moderate the cold and protect the plants from drying winds. Some growers have overwintered the cultivar ‘Arp’ in Zone 4 (to –30°F), but I still contend that’s risky business. Stick to the indoor treatment.

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