Soil preparation is key to successful landscaping. It takes time and some effort but pays off in healthier plants. Nearly all plants, whether shade loving or sun lovers, grow better in rich, loamy soil. Before you prepare the bed for planting, check the drainage. If the bed stays boggy and does not drain well, consider solving the problem with raised beds.
Lay sheets of black plastic over the garden bed. Hold down the plastic with rocks, bricks or scrap wood. The heat will kill any weeds or grass. Remove the plastic after a week in warm weather or two to three weeks in cooler weather.
Dig the bed to a depth of at least 12 inches; 18 inches is preferable. Remove rocks and debris as you dig.
Add required soil amendments. Clay soil needs organic material and sand. Add enough so the soil doesn't remain compact and retain its shape after you squeeze it in your hand. Exactly how much depends on your soil. Sandy soil needs organic matter so it holds water longer; again, exactly how much depends on your soil. It's difficult to add too much organic matter so be generous. A 4-inch layer would be adequate.
Spread gypsum over alkaline soil. Most desert soils are alkaline. A 2-inch layer should be sufficient.
Cover the new bed with slow-release fertilizer as the label directs.
Dig the bed again and mix in the ingredients. Start a trench at one end of the garden. Fill in the trench by digging another adjacent to it. Continue digging and filling the trenches until you reach the other end of the garden. This double-dig method mixes all the ingredients thoroughly.
Water the bed and notice any high or low spots where water pools. Level the bed by raking soil from the high spots to fill in the low spots.
Dig holes twice as deep as the containers of the new plants. For example, if the container is 12 inches, dig down 24 inches. Add in 6 inches of compost to the bottom of the hole and then replace 6 inches of soil. If the container is large, say a 5-gallon size that's 18 inches tall, dig down 36 inches. Add 9 inches of compost and 9 inches of soil. This extra digging and compost gets the plants off to a healthy start.