Nitrogen

• Nitrogen is the most important component in lemon tree fertilizer. Nitrogen provides nutrients necessary for healthy development of leaves, which will, in turn, provide the energy for the tree. Good sources of nitrogen are bat guano and blood meal.
  
  

Phosphorus

• Trees use phosphorus to increase fruit and root development. Your lemon tree will produce more lemons with increased phosphorus fertilization. Organic bone meal is a great source of phosphorus, as is phosphate rock.
  
  

Potassium

• Potassium aids the overall health of the tree. Sufficient potassium is essential for the flowering cycle of lemon trees, and it is the pollinated flowers that will turn into fruit. Potassium is also important for disease resistance. Organic potassium is found in wood ash and kelp meal.
  
  

When To Fertilize

• Lemon trees begin their growing cycle in February, so that is when it is best to start your fertilizing regiment. Feed one and two year old trees monthly, and older trees quarterly.
  
  

Method

• Fertilizing lemon trees is easy. Scratch the dirt around the base of the tree. Be careful not to disturb any roots, especially in young plants. Apply fertilizer, and water.