Hands down the most sensible article on blanketing horses we’ve read.
 
Some well intended horse owners blanket horses in conditions far, far warmer than they should be, unfortunately.
 
These simple guidelines from article from Penn State will help you know when it is appropriate:
 

“‘Should you blanket your horse?”

 
The long winter hair coat serves as insulation by reducing the loss of body heat and provides the first line of defense against the cold. Its insulating value is lost when the horse becomes wet and/or is covered with mud. So provide a dry sheltered area in cold wet weather. How do you know if you should blanket your horse?
 
Blanketing a horse is necessary to reduce the effects of cold and inclement weather when:
 
There is no shelter available during turnout periods and the temperatures drop below 5 degrees F, or the wind chill is below 5 degrees F.
 
There is a chance the horse will become wet (not usually a problem with snow, but much more of a problem with rain, ice, and/or freezing rain).
 
The horse has had its winter coat clipped for showing.
 
The horse is very young or very old.
 
The horse has not been acclimated to the cold (i.e. recently relocated from a southern climate).
 
The horse has a body condition score of 3 or less, or in poor health.”
 
(The horse in the photo is an image we received of an underweight horse in need of help some years ago. At Heart of Phoenix, we generally never have temperatures cold enough to require blanketing any but thin horses in rehabilitation)