I have no trouble starting my GC, in very low temps, without a block heater. You just have to master it. And, it's not that hard.
Rule no.1 is, if it doesn't start after a few seconds of cranking, STOP cranking. It's a diesel engine, it's not like your car. The only thing that will happen if you keep going is, the battery will die.
As stated, you need to give the glow plugs a good long warm up.
If it doesn't start after a short cranking, go back to the glow plugs, and run them for a longer interval.
You will also have to open the throttle sometimes when the air is very cold. Do NOT open it all the way as some manuals recommend. Somewhere around 1/4 throttle is usually enough.
If it does start, and it runs rough or smokes a lot, there is incomplete combustion, you probably did not run the glow plugs long enough. Try a longer interval next time at that temperature. If it still happens, you may have a bad glow plug(s).
If you do it correctly, it should fire off quickly, and run without smoking a lot. :thumbsup:
I made a video last year. At 7 degrees F, I gave it 40 seconds of glow plugs, and 1/4 throttle. It fired up just like it was a summer day.