Lemon trees like many citrus plants perform best when grown in a mildly acidic soil. They do not enjoy overly acidic soil, however so finding the sweet spot on the pH scale is important. Amending your soil at planting time and/or topdressing the soil once each year thereafter can help to maintain the optimal soil pH for your lemon tree irrespective of the natural soil conditions in the area.
Provide a soil pH for your lemon trees that fall between 5.5 and 6.5 pH. If you are in doubt about the content and pH of your soil mail in a sample of your soil to a testing service and they will give you a thorough analysis so that you understand the baseline conditions you are dealing with.
Amend the soil to be more alkaline and less acidic (bring down the pH) by tilling in the package recommended amounts of ground limestone, dolomite or hydrated lime.
Amend the soil to be more acidic and less alkaline (raise the pH) by tilling in the package recommended dose of ground sulfur or iron sulfate.
Water in soil amendments well at application time and keep the soil evenly moist to allow the movement of the particles down into and through the soil.