Many types of oranges that you may be familiar with, such as the navel orange and the common round orange, are categorized as sweet oranges (Citrus sinensis). These flourish best in U.S. Department of Agriculture plant hardiness zones 8 through 11. As the name suggests, the edible fruits should have a high sugar content and taste sweet. If you are harvesting only sour or bland oranges every year, one or more factors may be at fault.
Do not pick oranges too early. Ripe fruit will have skin that is smoother and less pitted to the touch, and will feel heavy for its size when you cup it in your hand. Allow unripe fruit to remain on the tree so that the flavor can develop.
Identify growing patterns of the unsatisfactory fruit. If the poor-quality oranges are being produced only on certain branches, prune these limbs back to the base once all of the good fruit has been harvested. This will allow the tree’s energy to focus on the branches producing good fruit. The branches that grow back may bear better results.
Remove all grass, weeds and other growth from around the base of the orange tree. Take a mature leaf sample in July or August, and have the boron levels assessed by an agriculture lab.
Fertilize the tree if the boron level is less than 36 ppm. Purchase a mixed foliar fertilizer containing boron, and apply a thin layer to the foliage once blooming is over for the season. Repeat the following season if necessary, until the leaf boron level is between 36 and 100.
Ensure that the orange tree is receiving enough water. Create a ring of healthy soil around the base, approximately 24 inches wide and 3 to 4 inches tall. Fill the ring with water every three days for new trees and every seven days for established trees.