I live in the suburbs in Charleston, WV. It's very hot and humid (in my opinion) during the summer but gets very cold in the winter. Although, today it is 60 degrees, tomorrow is supposed to be only 30. There isn't any farmland around me. This is the farthest into the winter that she's been itching, but it's been unusually warm this year. I use a humidifier when I'm home, but it's in a bedroom in the back of the house and she likes to spend the day in the front bedroom so she can look out the window. I won't run any type of appliances during the day, because I'm paranoid that something will happen (fire). People laugh at me, but I won't use a crockpot, make sure the washer and dryer are turned off, unplug fans or humidifiers, etc. I know, weird.
She didn't itch at all last winter. It lasted for a couple months at the end of summer/early fall. The only ingredients I could find on the shower spray that weren't specific was something like "plant oils" or "essential oils". I can't remember now. I had previously used a chemical-laden brand and thought that Method was supposed to be better. I e-mailed the company asking what types of oils they used so I could avoid them around my dog in the future, but they will not respond.
This year she started in June and has been itching for about 6 months. Then I started thinking that maybe it's the heartworm pills. I don't give them in the winter (mosquitoes need to be in 55degrees or higher for 2 weeks straight to carry it). I only give them every 6 weeks in the warm months, but I'm thinking of discontinuing them. It's been about 8 weeks since her last one, though. I don't like using them because they are a strong pesticide. My previous dog had major health issues, so I didn't give them to her for probably the last few years of her life, and she did fine.
I don't grow any plants of my own -- I'm a brown thumb not a green thumb. There could be trees or plants or something outside that might bother her. It doesn't go away when we visit family, though. They also live in WV, but they are in the very north (near Pittsburgh) and have completely different regional vegetation.
The parasite issue bothers me a lot, because there are a ton of wild neighborhood cats that like to come into my yard. Some days I open my front door and all I can smell is cat pee. They even started getting onto my roof. I started chasing them down with a flash light and a spray bottle of water. They quickly learned to back out of the water's reach. I then had to start running to the back of the house to get them from the other side, while Haley guarded the ground in the front and kept barking at them. I haven't heard them on the roof since the big showdown. I know they still come in the yard some, because as soon as I let Haley outside, she runs around the corner of the house to an area they run to when she chases them out. I figure they are bringing in a ton of parasites.
I don't use flea treatments on her very much, only when I see multiple fleas do I sometimes use it. So then I started thinking it might be from that, so I tried a different brand, went without any, bathed her in dawn dishwashing liquid (hated to do but flea med company told my mom's vet that it will take off all of the solution when her dog had a bad reaction).
I give her supplements for her immune system, probiotics, and good vitamin with digestive enzymes. SHe does get a little dry dog food, but it is Natures Variety, which I consider a good brand. For dinner she gets just lean meat, vegetables, and cottage cheese, so she doesn't have a crappy diet. I've changed proteins to see if anything makes a difference. Last year a friend gave me a bunch of deer meat. Her ears normally have a little odor to them, and that went away completely with the deer meat. She just got a new batch and started eating it on Friday, but I haven't noticed any changes in her ears. I've gone to all chicken then all beef and neither made a difference.