I'm a freak and will ride unless it is single digits. I rode on Wednesday when it was 11 degrees (in the indoor). The main reason is that my older mare is better off moving, and they just stand around outside due to icy/rutted footing out there. In the indoor, she is happy to move because the footing feels safe. I think it's good to keep them moving in the winter (especially the oldies). She drinks much better after being ridden too--that's important in the winter. Both of my horses are blanketed but not clipped and they don't sweat (even after a 45 minute ride with 80% trotwork). So I really don't think of that as an issue unless you have a horse with a heavy coat that will sweat up. On really cold days, I leave the quarter sheet on the entire ride--and they still don't break a sweat.
My routine for really cold winter rides consists of handwalking to warm both of us up, then I hop on and start trotting. We don't do as much cantering as usual, but lots of trotting. I know walking is great for them, but I can't stay warm when just walking.
When I lived in western PA, I discovered that riding/training below 20 degrees, even in an indoor, was unpleasant for me. The cold air couldn't be warmed as I breathed heavily and it irritated my respiratory tract. I figured it irritated my horse as well. So my cut off for actual work is 20 degrees F. Walking around is another story.
My personal preference -
I've ridden a LOT in cold climates, so I have frost injuries in pretty much all extremities. Feet, hands, thighs, cheeks, nose, ears. I start becoming uncomfortable once it dips below -15 c, that's 5 f, and I think I set a stop for things at -30, that's around -20 f. But then again, I live in Norway, and I know how to dress for the cold. Once it gets below -10 c my thermal suit comes on, and gradually scarves, sweaters, longjohns, face protectors and special riding mittens come on - and the riding boots are exchanged for huge leather boots with sheepskin inners. I must say I prefer driving when the weather really dips, as it's soooo comfortable sitting in a pile of rugs, not to mention you can bring hot chocolate in a thermos!! But I find it's all a bit easier if you don't look at the thermometer at all ... it becomes a lot colder once you actually know about the temperature
And additionally - some crazy research centre or other in Sweden has done research about what the horses can and cannot handle, and the results show the horses are basically unaffected by pretty much anything until -20 F, they don't recommend doing hard work below those temperatures. But fear for the horse? Take it easy, it's us humans that are weaklings!
Our lessons were cancelled if it got to -25C which is about -14F. Until that point it was always business as usual.
Now that I have them at home, I skip it when it's colder than about -15C (5F) unless it's a nice sunny day. Today is a beautiful, sunny day, and I will be going out to ride shortly. The temp is currently -8C (17.6F) windchill -12 (10F). It's practically a heat wave since last week; I can't wait to get out there and ride!
Why must you chastise my brilliant idea with facts and logic? **picks up toys (and wine) and goes home**
My own personal cutoff is usually single digits. It's just not fun when it's that cold. Seriously, if I can't feel my face - it's not fun!
I didn't ride Monday and Tuesday because our high temp was around 4 degrees, with windchills below zero. Screw that. I bundled my horse up with an extra blanket and handwalked.
I do ride when it's in the teens. I try and move around more than necessary while grooming and tacking up so I stay warm. I had a lesson Thursday night when it was about 15 degrees, and by the time I was finished warming up on the flat and ready to jump, I was actually too warm under all my layers.
Honestly, living in the Chicago 'burbs, if you don't ride in the teens then there's a lot of days you won't ride in the winter.
Oh, I do have an indoor ring to ride in, so that helps. It's not heated though, so it's pretty much the same temp as outside, just no wind.
I'm a wimp, but I also still have "Florida blood" as I swear I haven't adapted to cold weather despite being in Michigan for 5 years! Low 20's and below, I don't ride. Which meant that my horses had Sunday thru Friday off this past week. And you know what? They were fabulous today! They were both so happy and willing to work today! I think the full week off really benefitted them. I, on the other hand, was having withdrawals even though I chose to work tons of OT to keep me occupied. I don't "relax" very well Now in a perfect world, they would be at home with me so then when I didn't ride I could still do chores, snuggle with them, tuck them in at night, etc...
Gosh, I can't stand cold -I grew up in Minnesota, Colorado, New York, Vermont...and still can't stand it. So when my parents moved here to NC 12 years ago, I stayed....even though they moved up to Pennsylvania. Ugh!
Here in NC, I teach lessons year-round - I don't teach if the temperature and/or wind chill takes the temp down below 25 or 30 degrees. Most of the clients I have are children, and while none of the horses work hard enough to sweat when it's cold out, it's so sad seeing the poor 6 year olds shivering and teeth chattering when they're riding!! So I take pity and don't have lessons. Heck, some of the adults whine too.
I can usually stand to ride in temps as low as 25 degrees as long as there isn't any wind. Any. At ALL. But, I'm a wimp, and rarely will even go ride in that. I'm far more likely to teach in cold weather than I am to actually ride in it. Riding makes my face cold, even if I have my helmet face cover thing on.