Summer's heat and reduced rainfall translates into difficult times for making transplantation work during summer months. If it's a situation where you either move it now or lose it for good, then here's some tips that might save the day:
First, some caveats: never leave the roots exposed to the elements. Always keep exposed roots covered and moist.Don't move plants when you can devote at least 2 weeks of post-transplant time to caring for the plant.
Water the plants to be dug and/or transplanted the day before. This way the roots and stems will have enough moisture when time to dig comes.
If possible wait till evening or a day that is cooler and overcast.
If the transplant is going to a new home nearby, pre-dig the new hole of the appropriate size (at least 2x as large as the root ball, more if the existing soil is a heavy clay). Fill that hole with water before going on to dig up the plant.
Immediately before digging, water the plant to be moved again. Soak the area so the soil will remain in tact when it's dug up.
Place the transplant into the hole and fill it halfway with water. Let the water to settle the soil around the roots. Don't force the dirt or work it. Finish filling the hole.
Lightly firm the soil around the transplant.Don't stomp it down. Once all of the soil has been firmed into place, lightly water the entire plant again making sure to include spraying the leaves as well.
Shield the new transplant from direct sunlight for several days if possible with some light reflecting material (not plastic)..
For the first few days, check the plant daily. Transplants will need watering every day, if not more. If it is wilting, water the plant, but don't drown it. Depending on the weather and the plant, you may need to water twice a day until it becomes established. The larger the plant the more water will be needed.
The shock of being uprooted is stressful to plants anytime of year. In the heat of summer even more so. Taking extra precautions will help insure that the transplant survives the ordeal as best as possible.