Not all tractors come with a heater or glow plugs. If it is 20 * outside, then your motor is 20*. I want to add to those that have never used either, that you never keep holding the spray down. It can blow your motor if you spray too much. Try to spray a 1/2 of a second spray into the breather. Never keep holding the key and let the motor turn over and over as it can destroy your starter. These are not cheap. Always make sure your battery is charged up. First of all, make sure your tractor is in a safe place so that you can start your tractor this way because people die from starting tractors if standing on the ground. I never stand on the ground to start my tractor. Be sure it is in neutral or park. If the one -1/2 second spray didn't work, do two. Move fast to the key switch. If it evaporates, then you loose your boost. It will have a power surge at first, but do not use either if you do not need it. Keep your tractor in good repair; Keep your batteries charged, keep your cables strong, clean and tight on both ends.
If this spray didn't work, you need to charge your batteries- check cables, etc........
It is quick timing to make that spray into the breather, set the spray quickly on the hood keeping the spray wet; grab the starter, with my left hand; the steering wheel with my right, and start manipulating the steering wheel as it breaks free when the starter turns over; turning the starter all at the same time. It is a bit awkward if you have not done it before, but once it fires up, it will all make sense. I stand on my step of my tractor to do all of this as I can't reach anything from the ground as I am too short.
dieselbeef, In Florida it would be tough for someone to really know the need of a can of either in cold weather. A person that gets hold of a can of either that does not know how to use it, can blow the heads off of their motor or bend rods. Been a practicing amateur every winter when the temps drop low. I still have the same can from last winter, or is it from the winter before last????