Mulch is the best answer for both cold and heat. Don t put it too close to the stem, it may ring bark your exotic. I have rushed out and covered Camellias with newspapers in a rare snow storm. Now, I have too many plants to do this and have found they do not object to short snow spells. Fern leaves or bracken used to make a snug home, to keep exotics warm over the Winter months.
Heat is more difficult.
Nothing can be done when temperatures are way up and a strong hot gale is blowing. Early in the history of the country garden, we suffered these conditions. We were in the city when it happened and watered and watered the plants there. Towards the end of that heart-breaking day, we travelled down to the new country garden. I was suffering from a very bad dose of real flu.