I'm from AZ, and my diesel truck doesn't have a block heater. Due to an ill relative last year, I had to head north in January and was exposed to the arctic vortex. Temperatures plunged to 15 below a couple nights. I added some diesel fuel anti gel that I picked up in a local parts store. I never had any problem starting or running the diesel engine after it had sat in the cold weather for 10-12 hours.
The additive I used is listed in this link, and it is supposed to work down to -40 when used IAW directions.
Diesel Fuel SupplementIn Arizona, I often see temps in the 20s and don't have any issue getting it started. I don't normally use additive in Arizona.