4b but less than a degree from 4a.

The link below has a lot of information.

Here is a link that might be useful: Plant Hardiness Zones in Maine

Robin's technically right. However, just where you are located in Farmington might have a lot to do with your zone. If you are in town, you'll be a bit warmer than if you are in a slight valley or near a stream, since the cold air seems to settle in those pockets. I live a quarter of a mile from Wilson Stream and it get really cold :) Wind can have a real effect too---the UMF campus gardens, sheltered by buildings on all sides, are generally warmer than gardens which are completely exposed.

Good point. We have snow on the ground longer here than one half mile from here. I have three acres of open land. The field up the road is 100+ open acres with lots of sun, wind and degree or two difference. It makes a difference.

The zone maps are supposedly being redone to reflect things like radiant heat in newly developed areas. I've read that the change would be out last winter and then delayed until July but haven't seen it yet.

same here on MDI there are many micro climates with inthe island ranging from 5-4.

I have never seen a growing zone map that had any towns or cities on it. Its hard to tell in many cases what zone one is in without place names for reference. I would like to see one if there is such a thing. Anybody? fg

Wouldn't be accurate anyway. If it looks like you could be in one zone or t'other, it might be best to assume that your yard has some of one and some of the other. Actually I swear I have 3 zones in my yard. I suspect that in real life, those map lines are quite wavy and it's impossible to predict what direction they will wave in, from one year to the next.

Yeah, Cathy, but when a government agency puts Waterville in the same clime as Brassua Dam one has to wonder what their reason for existence is. fg