Well Southern California is a big place, are ya near the coast, San Bernardino Valley, Dessert, Foothills/Mountains? Knowing where exactly will help us have a better idea of what kind of climate we are looking at for plants.
A Good example would be if you lived in the dessert, then you would desire to have drought tolerant plants, if you are near the coast (Where the temperatures are not so extreme and there is a bit more humidity) you could get away with some sub-tropicals and even a few tropicals.
If your in the hills then you need to think frost and freeze resistant plants.
As a new gardener I can't tell you enough to make friends with your local Librarian and your Local Nursery person. The first is a good place to find the hundreds, thousands possibly millions of books on everything a gardener would want to know, the second would give you a good source of point blank Q&A assistance.
I prefer Organic Gardening (I have 2 acres in Modesto, northern/central Cali) and I use the more natural methods of cultivation ie I use lots of mulch so I don't have to weed, I make compost heaps, I use compost teas, my vegetable garden is intense, raised beds where I use succession and companion planting. No chemicals, no pesticides, herbicides or fertilizers. I'm full of ideas and information, just ask
As for those citrus trees. I would examine the soil before planting.
If you live where the soil is sandy, then I would strongly urge you to dig a hole twice as wide and 1 1/2 deep of the root ball, line it with sections of news paper (about 1/2 inch thick). Mix a ratio of 1 part compost with 2 parts native soil, fill the hole to the point where the tree root ball will be about 1/2 inch lower than the surrounding ground. Stamp on the soil, getting it packed in, then add more of your mix until the top of the root ball will be 1 to 2 inches below grade.
Then put the tree in the middle of the hole, open up the burlap, or if it is bare root just hold in place and fill in to about 1/2 full. Tamp with your fist the soil packing it in around the roots so the tree stands on its own. Grab the hose and fill the hole with water slowly.
The news paper will keep the water from draining rapidly, it will rot over time feeding the tree. So it acts like a biodegradable pot.
Once you get the hole full of water slowly add soil until you get the soil to the top of the root ball. If your root ball is 2 inches below grade then the soil should be that low. This will make a nifty water catcher which will keep the water from running off. As the tree grows its roots will push the soil up to level it off.
Depending on the size of the tree you may want to mulch those 2 inches with things like shredded paper, grass clippings, dead leaves, straw, hay, or bark. Mulch will help shield the roots from the heat of the sun and will help to hold water. As it rots it will feed the tree.
If it is clay, then you should dig the hole deeper to out 2 times the depth and 2 time s the diameter. Make up the same portions of compost and soil. At the bottom of your clay soil hole ONLY) ball up news paper into tight balls, fill the hole about 1/4 of the way then get inside and jump up and down on the paper, packing it in. What this does is provide a place for water to drain to so the roots are not standing in water. When ever a whole is dug in clay it is impossible to pack the soil back in to the same density to where drainage will not be a problem.
Fill until the root ball sits about 1/2 inch ABOVE the ground level. jump in and pack the soil and repeat as with sand aiming to have the top of the root ball about 1 inch above the ground level. Do not fill the hole with water until you have put in soil to about 2 inches below grade, then fill with water. This will help the tree to shed water and not collect as much which will sit around its roots and kill it. Again mulch (mulch is a good thing)
If you are in an area with rabbits, deer or other bark eating critters, wrap the truck snuggly (not tightly) with aluminum foil up to the first branches. keep it on until the tree is 3 years old (at least) or until the trunk is at least 2 inches in diameter. You may have to replace it once in a while. As the tree grows make certain that the foil isn't getting tight, that will kill the tree.
If you live in an area that has light frosts, in the fall fill up plastic milk containers with water, set about 3 or 4 around the trunk with an inch or two of space between truck and milk container. During the day the water will absorb the heat of the sun releasing it at night keeping the tree warm through the mild frost.
Feeding and watering. If you follow the hole making above you shouldn't need to water unless you live in the dessert. If this is in a yard then the watering you do for the lawn is enough. If this is in an area that doesn't get water regularly, in a dry area, then soak the tree once a week for the first summer.
Feeding. Compost. The gardeners back gold. Compost is easy to make and it is far better than any fertilizer you can buy. You can get compost in a bag if you don't want to make your own.
Make compost tea, that is about a shovel full of compost to 5 gallons of water. Let it sit over night and pour the water on. that will carry enough nutrients to feed any plant.
I think that pretty much covers it.
CHeers
David
AnswerPool.com 
