[Vwdiesel] could I need new glow plugs?

[Jason and Lori Stoffer]

Hello,
 
I own a rabbit pickup with what I believe is a golf diesel engine.  I depress the (manual) glow plug button for 45 seconds as per the previous owners instructions, turn the key and it cranks but never fires. It will only start if I plug it in for at least an hour or if its 90+ degrees outside. Could I possibly need new glow plugs?.  Any help would be much appreciated. 
 
Jason