I don't ride in summer. I hate the heat but not only that in australia you got 100000000 flies to deal with too!! Your trying to ride nicely so you can get off on a good note, at the same time trying to swat flies and hold the reigns, and trying not to lose the plot!! I hate flies, I hate the heat, so I won't ride. On cooler days I would ride about 6/6.30 at night and usually trail ride. My horses got no comps on during summer so they get to rest :)
I did have to start riding my older horse ozzie in january because he was getting REALLY fat and cresty. LOL but that was it.