Timing

• Young trees need fertilizing about three weeks after they are planted, when their buds being to swell, according to Jane Morse on the University of Florida IFAS Extension website. For the first year, gardeners should fertilize every six weeks during the growing season. Older trees typically need fertilizer just three times a year -- in late winter, in May and after the growing season.
  
  

Types

• A fertilizer with an equal ratio of nitrogen, phosphorus and potassium -- such as an 8-8-8 fertilizer -- is healthy for most citrus trees. Morse recommends fertilizers that also contain other nutrients such as boron, copper, magnesium and manganese.
  
  

Method

• Gardeners should spread the tree fertilizer beneath the tree, with some fertilizer beyond the canopy to ensure all the roots can access the nutrients. The University of Florida Extension recommends an even spread, without building the fertilizer up around the trunk.