Take more time warming up and be careful before starting to jump- cold muscles take longer to start working properly! I also have a quarter sheet for my horse that I'll throw on during warm up when the temps are below 15F or so. If it's in the negatives, I would say keep your ride short and light unless you have access to an indoor or a warmer area to ride.
Hey Lily! In the winter since my horse is a little more distracted and sharp, I like to do a lot of dressage flat work to get him thinking and working with me. Serpentines, circles, spirals, lateral work, etc.
I do less walk and more trot in my warm up during the colder months. I find it helps get the initial ‘spark’ out of my horse! He is sharper during the winter.🙂
My horses are more energetic when it's winter so I take my time warming up, In winter I do more dressage than usual and before jumping I like to do some poles and cavalettis.
From my experience, horses are more fresh during the winter, so I'd take more time warming them up. More walk, and trotting circles and serpintines, and engaging the horse's back end.