over wintering calendula - lowest temps

REMF33

Hello I am struggling to find an answer to what lower temperatures calendula will tolerate.
The background to this question is that I sowed some in autumn and they were doing well - healthy, slow growth etc, but now have mildew. (The bane of my gardening life but not usually in this context!) They are currently in a largeish unheated but enclosed area with a minimum temperature of 1C (presumably when it was -7C outside). I want to sow broad beans and peas which I will initially grow on in this area but am concerned about contamination. I could move the calendula to a cold frame in a sheltered spot (south facing covered but otherwise balcony) but it's still likely to go lower than 1 up there.
Anyway, any ideas about temperatures? There are several different varieties - Neon, Snow Princess, Indian Prince, Porcupine, Kinglet mixed. They can all be resown of course, but I might as well give them a chance.

AnniD

I did find this old thread - see @nutcutlet's reply. Don't know if this helps.
Hopefully someone will have personal experience,  l treat them as annuals and don't sow until Spring. 

https://forum.gardenersworld.com/discussion/157955/can-i-overwinter-marigolds

Astro

I have overwintered them both left in the ground and in greenhouse. I've found they are tolerant of low temperatures, With that being said they have often had mildew and/or looked generally tatty come late winter early spring.

 I've personally just pruned them back and fresh growth comes through , they have the benefit of having grown good roots since autumn. 

REMF33

The autumn sowing was an experiment which may or may not be repeated! 

Thanks both.