Orange trees need soil with a relatively neutral pH in order to thrive. 5.5 to 6.5 is the ideal range. however, it is possible to grow orange trees in acidic soil, as long as you spend some time and attention amending the soil to make it more alkaline. Once the pH falls below 5.0, orange trees can suffer from magnesium, calcium and phosphorus deficiencies. These deficiencies will result in a shorter tree because the growth is stunted.
Choose a planting location with well-draining soil. The soil should be deep because orange trees have extensive, deep root systems.
Plant orange trees 25 feet apart for best results. Give the trees water every other week. Long, deep waterings are better than short ones because the water will reach the roots. It is especially important to water the trees during dry periods. Stop watering in the fall, so there are no new buds right before winter.
Test the soil at the base of the orange tree. Get a pH test kit from a nursery or planting center. Take a few soil samples from around the tree and mix them together. The test kit will have instructions specifying how much soil to collect. A few samples is a good idea to get an accurate reading.
Use the test results to determine how acidic the soil is and what nutrients it needs. Orange trees cannot grow in very acidic soil with a pH below 5.0. The best conditions are between 5.5 and 7.5.
Add hydrated lime to boost the pH and make the soil more alkaline. Different soil types react differently to lime, so they need varying amounts. If the soil is sandy, add 4 oz. of lime per square yard. For loamy soil, add 8 oz., incorporate 12 oz. if the soil is clay-like in consistency, and 25 oz. per square yard in peaty soils. Mix the substance into the soil with a rototiller or garden hoe, being careful not to go deep enough to damage the plant roots.
Add organic compost or manure to the base of the orange trees after the fruit is harvested. This will make the soil more fertile and more adapt for orange plants.
Test the soil annually to determine if the pH has become less acidic. If it continues to fall below 6.0, add the hydrated lime after the oranges are harvested. Once it is higher than 6.0, you can stop the applications.
Fertilize the orange plants with a complete blend each spring. One with a small amount of nitrogen is a good choice because it will help lower the pH. Follow the manufacturer's instructions.