For many years, I had at least one rosemary plant which I would take indoors
for the winter. On the whole, rosemary bushes do not like spending the winter
in a dry house. In such an environment, they hold on to life for a year or two,
but soon give up the ghost.
A few years ago, I discovered that the most important way to succeed in overwintering a rosemary plant is to make sure it is stored in a humid-enough
environment. Strangely, for a plant that originates in the Mediterranean,
it can actually do without light for months, but not without humidity. I
discovered that when I was going away for the good part of a winter. In late November, I potted up my rosemary and
stored it in a crawlspace where there is no light, quite a bit of humidity and temperatures that do not reach the freezing point. I had little hope that
the plant would survive but, to my amazement, it came out in the spring
looking much better than it ever had done after a winter indoors. All it needed before
another season out in the garden was a bit of trimming.