I just use oven cleaning gel - smear it on, leave and hour, and the very toughest black burned stuff just rinses off.
Of course that's no doubt 'ecologically unsafe' but I've found the gentler things don't work when I've forgotten a pan and its contents have turned into Devil's concrete.
Works on ovens as well 
Do you get emotionally attached to the plants in your garden ?
Only 50% of middle age adult manage more than 1 brisk 10 min walk a month.
