Citrus trees can be pruned any time of the year, except in the winter for outdoor trees. The trees can be pruned for shape and to remove dead or erratic branch growth. A well-pruned lemon tree has a higher fruit yield and has less branch breakage.
Citrus trees require minimal pruning to be kept vigorous. The trees tips can be pinched back where the most vigorous growth is occurring to stimulate fruit growth. Fast-growing shoots should be removed when they appear near the main branches. Those branches are unwanted as they don't produce fruit. Thorns can be pruned off if desired.