Urban soils can make gardening very tricky. For plants such as citrus, roses and avocados, acid soil is essential to proper growth and development. When the soil is determined to be alkaline instead of acid, measures can be taken to reduce the soil's overall pH. Keep in mind, however, that the soil's pH can only be changed by one full point in one season, so severely alkaline soil will require multiple treatments for years before proper acidity is reached.
Test the soil's pH to determine how alkaline is the soil is currently.
Add 1.2 oz. ground rock sulfur per square yard for sandy soil and 3.6 oz. for other soil types, if the garden will not be considered organic. For organic gardeners add 1 inch organic matter such as sawdust, leaf compost, peat moss or cottonseed meal.
Till the soil to a depth of at least 2 feet to ensure adequate combining. Repeat these steps over each growing season until the soil reaches the desired pH.