Answer: Some varieties of lavender are hardier than others, so it depends which kind you have. "Munstead" and "Hidcote" are among the hardiest. They hate wet feet particularly in winter and will have the best chance of overwintering in a well drained alkaline soil. Assuming you can protect the plant from wind, the danger with a planter box is that the soil mass will be too cold for the roots since it is not insulated down in the ground. If you can insulate the box or grow the lavender in a larger container, it will have a better chance of surviving outdoors. It is difficult to overwinter lavender indoors because it needs very bright light to grow well and stay healthy. If you have to bring it indoors, try to keep it in as bright and cool a location as possible.
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