I have been gardening here in Phoenix for several years and have had some success. But I still haven't figured out how to deal with the intense summer heat. Every summer when the heat gets real bad (above 105) a lot of my plants get knocked back hard. I have a grapefruit tree (about four feet tall) that grows very well all year round and then just gets hammered in the high heat, leaves shrivel up and die. The same thing happens to my bower vine. any suggestions on how to deal with the extreme heat?