I have some potted mint plants at home in Glasgow, Scotland. I left them with a friend over summer and he plucked the leaves from the middle of the stem as a frequent snack thus the plant became leggy and naked, and ugly. The plant also started browning throughout the stem and leaves in the middle of the pot and that soon spread to the rest of the plant. I chopped it down to the base and about a month later, it grew again, but the leaves were never as big as they used to be and the plant started browning again. I have just chopped it down to the base again. What is wrong with it? Can it be saved?