In the South we do tend to complain more about the Summers. It does get so hot that it's not worth riding. Brutal for the rider, but even worse for the horse. You can do things to ride and keep warm in cold weather. Horse will warm up from the ride. All I want to do in the Summer when it's 98 with a heat index of 110 is let the hoses stand in the shade and put a water mist or sprinkler over them with a fan blowing. Early morning or late evening is the only time that's almost cool enough to be tolerable, but that's when the blood suckers are most active, so there's really no winning in the Summer.
Is it any wonder that we love Winter riding :))