Cactus / asterias seedlings

The temperature in my greenhouse went down to less than 3 C' in this morning.
I have stopped watering to my cacti a while except seedlings.
You have to keep pottingmix as wet for seedlings through a year.
The photo is one year and nine months old Astrophytum asterias cv miracle kabuto seedlings in a 10 cm square pot.
They do not stop growing in winter.