Answer: For most herbs, it's best to collect the leaves for drying or other uses just as the flowers are beginning to form. This is when the leaves have the maximum amount of the desired essential oils. It's possible that the spots you saw in the fall were just the naturally drying off process as the plant readied itself for its dormancy period. If the new growth looks good this spring, the plant should be fine. Mints are, as a rule, quite durable and carefree.
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