Answer: Plants are usually able to adjust to summer temperature swings as long as they are well-hydrated. Watering as often as necessary to keep the soil from drying out is a good first step. Shielding the plants from intense sunshine will also help - if they are in a sunny spot. One more step your cousin can take is misting the plants in the morning and again in the late afternoon. This will combat dry air and help keep the plants from dehydrating too quickly. Most plants will simply stop growing when temperatures hit 90F and they will remain in this state until things cool down. They may not flower in hot temperatures, but the stems and foliage should be okay. I'd just advise your cousin to continue to give the plants good care. When the heat wave is over, the plants will probably resume growing. Anything killed back can be pruned away.
Best wishes with your garden!
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