Well obviously winter, unless you have the really hot days. But it depends on where you get your good weather and bad weather, if its quite cool and its the middle of July and your horse is just standing in the stable, you can't just leave it with no rug on, so just a thin sheet would be just fine but when its raining and still, it could be summer and your turning your horse out, it would probably need an outdoor rug, especially if its cold.
If your horse shivers from the cold in the winter, you need a blanket. some horses get cold easy other don't. If you live where you don't get snow I would just let your horses grow there extra hair the natural way, but if you live where it snows you should put the blanket on.
Horses may need a blanket in the winter if you clip their coat, robbing them of their protection from the cold. Blanketing is bad for the horse however, but it is the lesser of 2 evils. If you touch your horses ears and they are cold, he is cold. If not, he is not, so leave him unblanketed.
u should only put a blanket on during winter. later fall and early spring u can have a light blanket on. horses do grow there own winter coat that is (don't quote me on this but) 10x warmer than a blanket and you should let them grow that for a little before u put a blanket on them. also younger horses do not need a blanket they should grow there coats out.
usually winter when it gets cold out. sometimes for horses health or medical problems.
it depends on the weather,season, and the kind of blanket
winter and fall but mostly winter
Winter
near the winter time
Winter I should imagine.
Usually you'd get your horse a new blanket in late fall or early winter. Or what ever the coldest season for your region is.
There are two answers to your questions:If you are asking "if you need a blanket under a saddle" then, yes. It is to protect a horses back.But, if you are asking "if you need a full body blanket to keep a horse warm" then, no. Unless you are in Norway and you have a very thin coated horse.
No they don't, as it gets colder you have a winter blanket. And your horse should also have a spring blanket as well.