Day 28. My soul mix looks too hot to me. I eyeballed the ingredients. Oceans forest soil, once used ocean forest (used in previous grow),worm castings, and perilite. Watered with recharge. When transplanting I put recharge around the roots. My guess is to much worm castings. Maybe overwatered.
Dude, add more soil, mulch and shit around it (without necessarily like heaping soil against the stem), give it a bit extra sugars/carbs, calcium, phosphorus, vitamin E.
No jokes, it keeps the roots quite a bit warmer (like even just for water retention, other than extra insulation, which might seem counterintuitive, but aids thermal regulation), phosphorus and sugar for heat/internal energy. Calcium to "buffer" things and aid phosphorus and other uptake. Vitamin E for cold resistance.
I've grown several hundred plants through winter, sometimes as cold as -6c (still warmer than some other places).
Cheers, and good luck. I'm currently doing winter grow (germinated seeds at worst time possible, start of winter).