Orange trees are one of the most heavily feeding plants. In order to produce an excellent fruit yield, they require not only a standard fertilizer, but additional nutrients and even fungi fertilizers. For a healthy orange tree, use the following fertilizers and supplements as directed.
Fertilize annually with an equal amount of nitrogen, phosphorus and potassium. These nutrients can be found in a standard balanced, or 10-10-10 fertilizer. Slow-release standard fertilizer is more beneficial for citrus as it ensures that the nitrogen does not wash below the root line. Standard fertilizer should be applied and watered in annually.
Supplement annually with additional nutrients including magnesium, boron, copper and zinc. These trace elements are found in turf fertilizers. Similar to the balanced fertilizer, these nutrients should be applied and watered in annually.
Incorporate Mycorrhizal Fungi into the soil. Mycorrhizal Fungi attaches to a plant's root system and enables them to gain more nutrients from the soil. This fungi tends to be absent from most urban soils.
Test the soil and if necessary, supplement annually with iron supplement tablets. If the tree's soil is above a pH of 7, then iron must be added to the soil.
Incorporate Mycorrhizal Fungi into the soil annually beginning two planting seasons before planting the orange tree.
Incorporate fish emulsion fertilizer into the soil bi-annually beginning one planting season before planting the orange tree. For best results, fertilize initially in the spring as the tree is budding, and again once its fruit has been harvested.
Mix 5 cups of hot water with 1 pound of coffee grounds and let sit overnight. Pour onto the tree's root system annually at the start of spring for added soil acidity. For best results, consider applying at night and watering in well.