The desert is not like many other places that have a decent amount of rainfall per year and can go over 100 days without seeing a drop. It is necessary to provide some water to your plants and can depend on several factors such as temperature and your soil conditions. Know your soil and if you have to water more frequently. If your plant looks droopy or turning yellowish, add some extra water. Check the soil near the base of the plant and see if it is dry.
Do not fertilize when you first plant into the ground, this could burn the roots and possibly send the plant into shock. Fertilizing is not necessary for trees as we live in the desert and there is a lot of heat for them to grow. If you would like to promote a faster growth at the beginning, it is ok to fertilize for the first couple years. Citrus is the exception and fertilizing should be done 3 times per year starting in mid February. A good way to remember the times of the year to fertilize are Valentines Day, Mother's Day, and Halloween.