Loori - I have looked up 'Swiss mint' and it seems to be a variety of Mentha piperata - peppermint. In order to grow it successfully it is useful to think about what this plant's natural conditions would be. In its native habitats M piperata would obviously live outdoors with ample light. It likes moisture but not stagnant water. It is a perennial so it is designed by nature to die down in the winter and regrow from its roots in spring. In the UK it goes down to overwintering green stolons and does not completely disappear like M spicata. It is a European native and is happy in temperate and continental climates so is quite capable of enduring very low winter temperatures. Bearing all this in mind try to think of the best place you have for your plant. If you have a garden outside planting it in the soil would be best. If you only have a balcony I would put it out there. If the pot is likely to freeze through for any length of time I would wrap it in something insulating when frost is expected just in case. Although mint can be kept indoors in the winter it will shorten the life of the plant because it will get no winter rest and it will be struggling against poor light, overheating and probably too much water. I have a pot of mint outside my kitchen door and it is left out all winter. temps last winter went to -5C once or twice but that is unusual for here. 7c would not bother your mint at all. (Remember most people on this forum are in the US so when they say 0 degrees they are talking Fahrenheit ie VERY cold.)

Well, it's apparently not so good for cattle to ingest: Cattle do not normally feed on dogfennel, but they may eat it when more suitable forages are lacking. However, the leaves contain low levels of the toxin tremitol, which causes dehydration when ingested by cattle. Dogfennel is currently the number one most commonly occurring pasture weed in Florida. I can't imagine it would be all that good for humans.

i live in SF and planted up a tiny pot of mint. It seemed like it wasn't going to make it through summer and was drying out...but our summers here are very cool and wet (unlike the end of spring) it becomes overcast and wintery in summer. I live in one of the warm microclimates of town, yet still overcast for most of the day. I didn't give up and increased watering even through "summer". Now it's becoming quite bushy, I think it really likes the cool air and loose moist soil.

rhizo is right about the white substance outside the pot. I have them on my pots. Looking at the dried stems and leaves, is it possible that your mint needs more water? My mint looks patchy like that when I forget to water. Like you, I have my mint by a south-facing window. It does well there as long as I remember to water