During the summer, in my area the temps can reach up to 110*F. If I'm not on top of my plants, they can easily dehydrate and die. However, like Cindysid mentioned, as long as you take care of the roots you'll be fine. The way I do this is by digging a small basin around my plants to hold in water, and I also apply a one or two inch layer of mulch. This helps keep the soil cool and cuts down on water loss from evaporation. I also use soaker hoses, so water stays near the root zone and gets released slowly. You could also use drip irrigation or buy water holding crystals.
Where you choose to plant can also make a difference. A old garden tip that was given to me years ago: "always plant on the south side of the mountain." This way, plants get full sun in the morning and indirect sun during the afternoon. The mountain can be a house, a tree, or even a fence. And if you have to, you can also buy gardening fabric and cover your plants with that or build a make shift green house out of PVC or lumber. Fabrics usually allow 70%, 80%, or 90% light to go through. Go to your local nursery or garden center and see what they use.